Furnace - Limit Switch | Repair and Replace

[@bruceforsman4812]

simple direct no nonsense video perfect. I just repaired my furnace with zero previous knowledge of hvac.

[@AmreSupply]

Thank you for your comment Bruce Forsman! We're glad this video helped you repair your furnace.

[@onebladeprop]

Excellent video. You explained what it does, basic trouble shooting, and replacement in the amount of time others would spend padding the video with the history of coleman-evcon. Thank you

[@AmreSupply]

Thank you for watching! We're glad you found it helpful! We try to make all of our videos informative and concise and we have many other videos on our channel as well. If you're curious on learning more we recently released a series on Water Heaters, including a video on How Water Heaters work: kzbin.info/www/bejne/eHm4gXmCl8drhLs Cheers!

[@p.chuckmoralesesquire3965]

Thank you for this. Woke up this morning to no heat from the 1990's Amana 90+, but had airflow and on/off was working. I opened the bottom up, saw blink code 4 blinks, which indicates filter/or high limit switch. Replaced the filter, pulled out the limit switch and tapped it in my hand a few times and GOOD TO GO!

[@AmreSupply]

You're welcome Justin, we're glad the video helped you get it running again!

[@SRFDriver]

What a well thought-out and explained video. Thank you very much for taking the time to create this.

[@AmreSupply]

You're welcome SRF Driver and thank you for your great feedback, I'll share this with the rest of the AMRE video team! Cheers!

[@jamesjamari3449]

I know im randomly asking but does any of you know of a way to log back into an Instagram account?? I somehow lost the login password. I would appreciate any tips you can offer me.

[@blazecole6376]

@James Jamari instablaster =)

[@jamesjamari3449]

@Blaze Cole i really appreciate your reply. I found the site on google and im in the hacking process now. Looks like it's gonna take quite some time so I will get back to you later with my results.

[@walterlueke8020]

Vance, Great Video! You've been so helpful with other comment, I've decided to ask you. I have 2008 Furnace Lennox G51MP-36B-070-08. The Primary Limit Switch is hard to replace mounted on the wall behind the intake vent and the exhaust vent (you probably know this configuration). The Primary Limit Switch is a L210-30F. The furnace ran great with occasional lockouts , but then in Jan. - Feb. 2021 every few days or so it would lock-out with error code that says either "lost flame sense more than 5 times" or "Primary Limit Switch Open." So first I cleaned the Flame Sensor, and that helped for a few weeks. Then Lock-outs with same error code began again, but the Combustion Air Inducer (CAI) keep running after lock-out (somewhere I read this is caused by the Primary Limit Switch staying Open). Since it is easy, I installed a new Flame Sensor, but it would still lock-out every three days or so, but now the CAI motor stopped running after lock-out. So now I'm thinking the Primary Limit Switch is the next thing to replace. How many minutes can these furnaces run until the Primary Limit Switch opens and shuts them off? Can I substitute a Primary Limit Switch with a higher rating say L250-30? Is there a Lennox forum? Any advice will help. thanks!

[@AmreSupply]

Hi Walter, thanks for watching, we're glad that you found it helpful! If you're getting a flame sensor error code, then there's a few other things to check. For the flame sensor to work it needs to complete the (DC) circuit, from the control board, through the flame, into the metal of the burner and down to ground through the furnace frame. So the furnace needs to be grounded properly and the burners need to be clean for the flame sensor to work properly. Give the burners a cleaning and you can also test for continuity from the metal of the burner to the furnace frame to be certain. When replacing the limit switch, you have to match the ratings exactly for the furnace to run safely. The lockout times differ between furnaces, there is some variation. There might be a Lennox sub forum on one of the HVAC discussion boards if you do some searching. Hope this helps.

[@walterlueke8020]

@@AmreSupply O.K., I'll let u know. Thanks!

[@SSBARBEL]

You are amazing! Worked perfectly and easy to do! Very good video as well! Thank you.

[@AmreSupply]

Thank you for your kind words Charles! We're glad the video helped you out!

[@HiddenZblade]

I had one technicians found out the limit switch is defective. He didn't even bother taking it out to diagnose the darn thing or take pictures. I scoured ebay,Amazon and other website to email him the parts. He keeps on saying they're not the right parts--NO. Wanna know what I did???? I don't care how many positive reviews his company received. I gave a 1/10 rating. That was July 2021 during the abnormal summer heat in Vancouver,BC. Second time this October. Another technician finally took photos of the limit switch and in process of finding replacement. I texted him to email me the pictures so I can help out. You know what he replied? "Go find it yourself." I have no knowledge with electrical/mechanical equipment thatz why I called for hvac technicians to do their job. They just take my money and leave. I'll take out the damn thing myself and find replacement. It's a learning experience indeed.

[@AmreSupply]

Thanks for sharing your experience. Even though there are some great technicians, there are others that don't offer the same level of customer service. The limit switch is simple to replace. You can match by part number or by the rating on the switch. A L180-40 means that the switch will open at 180°F and close once the temperature drops 40°F (at 140°F). These ratings need to be matched exactly. www.amresupply.com/catalog/Fan-Limit-Controls-HZ3D As well if you want to improve your knowledge of electricity and multimeters this 10 minute video will help explain the concepts in more detail: kzbin.info/www/bejne/qJDQmpqZqcaSf9U as well this video explains appliance components: kzbin.info/www/bejne/m5CUoYKNiLuInMk

[@rajvosa59]

When I went to Amre store in Hamilton Ontario and explained my problem...she said if you part what you need or part number than I can help. I said..I have red light flashes once and points to Limit circuits...or switch...but she said I don't know I am not technician...ohhh well .. thank you

[@AmreSupply]

Thanks for watching. Our staff do have a variety of experience but are not technicians. They can't diagnose problems while at the counter but sometimes will share their thoughts or suggestions depending on the problem. If your codes point to a problem with the limit switch and you've replaced the air filter, then it might be best to install a new limit switch. On the side of the limit switch is a part number. Sometimes you can search by this part number directly. www.amresupply.com/catalog/Fan-Limit-Controls-HZ3D In other cases you might not be able to find an exact match. You can match by size and shape, and the rating on the side of the switch. For example you might see something like "L210-30F". That means that the switch has a high limit of 210°F and will open the circuit at that point. Once the temperature drops 30°F the switch will close, and reset. Hope this helps.

[@adamhmitchell2010]

Seriously nice production quality on this video 👍. Well done.

[@AmreSupply]

Thank you Adam! Quality matters in these videos, and we're glad you found them helpful!

[@basemmaddah5753]

Great video and instruction how to test if the limit switch is defective or not

[@AmreSupply]

Thank you Basem, we're glad that you found the video helpful!

[@bentremy]

Thank you very much. Great video, no nonsense to the point.

[@AmreSupply]

You're welcome Bent! We're glad you found it helpful!

[@sonnynguyen8012]

Thank you for useful video. Now I know the limit switch in my furnace.

[@AmreSupply]

You're welcome, we're just happy to help!

[@AmreSupply]

If your furnace starts, then stops (short cycles) then it likely a problem with one of the safety switches. Learn more in this video: kzbin.info/www/bejne/mGHWcnqqYpahn7c

[@christopherfisher123]

Thanks this helped even though it took me forever to find mine.Mine was behind the filters on the backside of the blower housing. LOL it was almost as bad is working on a sink.

[@AmreSupply]

Yes not all furnaces are as easy to access as others. Glad you found it!

[@lynette5382]

Same here right now

[@canaj7]

NO WAY THIS GUYS NAME IS VANCE! JUST LIKE THE OFFICE!!!!!!!!!!! VANCE HEATING AND REFRIGRATION

[@lincolnmicrophonellc]

Bob Vance, Vance Refrigeration.

[@jimbarron8688]

If the blower motor cycles on and off ( 46 sec.) its got nothing to do with the limit switch. The limit switch will detect the heat rise and shut off the gas valve. The main blower will run throughout in an effort to cool the furnace down. To confirm this simply detach one wire from the limit and watch the blower turn on.

[@AmreSupply]

Thanks for watching. We did another video to explain the cycling on and off which can be caused by a few different components depending on how far into the startup sequence it gets. kzbin.info/www/bejne/mGHWcnqqYpahn7c

[@gregrogers6012]

Very helpful. Appreciate your helping with my questions.

[@AmreSupply]

Thank you Greg, we're just happy to help!

[@brinnswft]

Vance is my hero

[@AmreSupply]

Thank you Brian!

[@panchogonzales6409]

THANKS YOU JUST SAVED ME A COUPLE HUNDRED DOLLARS !

[@AmreSupply]

Thanks Pancho Gonzales, glad the video was helpful!

[@reshadhadi3882]

Hello, I am following and watching your video really they are very useful. At the same time, I have a suggestion that there is a very bad noise (melody) at the beginning while opening the video if you could change it with a soft melody. Thanks in advance

[@AmreSupply]

Thanks for watching, we're glad that the video helped you out. Other people have pointed out that the sound is pretty loud. It does depend on the speakers that you're listening from. Our newer videos have an updated into that is quicker and a bit softer. kzbin.info/www/bejne/iKKYqnuvfpqIh6M

[@mohammedmirza3614]

Thank you sir for the valuable knowledge.

[@AmreSupply]

You're welcome Mohammed, we're glad that you found the video informative!

[@FusionDeveloper]

0:43 dang, if only I found this video before I bought a replacement relay switch. Thanks for explaining it. (update, fan still runs 24/7) 10/2020 update: A/C tech said the problem was actually the fan motor itself was stuck permanently on and had to be replaced. The fan was replaced and now it works properly.

[@AmreSupply]

You're welcome! We're glad you found the video helpful!

[@FusionDeveloper]

@@AmreSupply Installed new one today, it did not fix my problem. The PAYNE A/C fan still runs 24/7. Installed these 2 things: WARREN TECHNOLOGIES AUTO LIMIT SWITCH L165 (312403/T-O-D60TX11/1644) L165-40F Song Chuan 832AW-1A-F-C1, 24VDC Relay, 240 VAC, , 30A General Purpose Relay. fan still runs 24/7. Doesn't matter what the AC is set on and doesn't matter if it is connected or not. All I know, is there is a black wire inside the air handler, and if i unplug it, the fan stops. I replaced the thing the black wire plugs into (relay) and it didn't fix it, so i saw your video, replaced the limit switch, still runs. Any more ideas?

[@ccf805]

@@FusionDeveloper Did you fix your problem? I have the same problem...fan continuously runs on my Carrier central heater. I was going to replace the limit switch however, it measures 0 ohms between terminals. Looking at the furnace schematics, it seems like it should be "open" when cool (fan de-energized) and "close" when warm (fan energized).

[@FusionDeveloper]

10/2020 update: A/C tech said the problem was actually the fan motor itself was stuck permanently on and had to be replaced. The fan was replaced and now it works properly. ((I previously had replaced 2 electronic components on the circuit board, a temperature detection thing and a relay switch and it made no difference.))

[@ccf805]

@@FusionDeveloper Thanks!

[@kamalnasari8632]

Thank you for your kindness to respond. 👏👏👏👍󾓦✟✟✟󾓦 USA

[@AmreSupply]

You're welcome Kamal.

[@stevegovea1]

Thank you... You got yourself a new subscriber.

[@AmreSupply]

You're welcome Steve, we're glad that you subscribed! We did some videos on water heaters that you might also find helpful, these are also on our channel: kzbin.info/www/bejne/eHm4gXmCl8drhLs

[@James-ng1os]

Thanks a lot,this video helped out a lot

[@AmreSupply]

You're welcome, we're just happy to help!

[@hawkeye7435]

THANKS FOR VIDEO...

[@AmreSupply]

You're welcome!

[@mariogarcia7490]

You saved me a lot of money...thanks for the video

[@AmreSupply]

You're welcome Mario!

[@ulisesmeza8494]

AMRE Supply m le

[@PBS-nm1uu]

Nice you did the most important part testing it thanks great presentation.

[@AmreSupply]

You're welcome, we're glad you found it helpful! In all cases that its possible we try to including continuity tests in all of our repairs videos.

[@mts7274]

Will the blower motor still work if the limit switch is bad? Or can a bad limit switch prevent the blower motor coming on, even if just using the furnace on the "fan" setting?

[@AmreSupply]

Thanks for watching. The blower fan might still run but it might cycle as the furnace attempts to ignite: kzbin.info/www/bejne/mGHWcnqqYpahn7c

[@shokid]

Mine cycles on/off only on cool, furnace works perfect. Would the limit switch work for cooling cycle as well? I’ve replaced the control board but doing the same thing. Maybe it’s defective 🤷‍♂️

[@AmreSupply]

Thanks for watching. The limit switch is a safety device so it is meant to protect the furnace from an unsafe condition. In many cases this will still be wired into the cooling circuit so it is possible that it is causing problems.

[@shokid]

@@AmreSupply thank you!!

[@tntheatingandairllc]

Great video very helpful

[@AmreSupply]

Thanks for watching! We're glad you found it helpful!

[@jindo333333]

Hi. Vance. I wanna order limit switch but you have two different limit switches on your online. One is manual reset and the other one is auto reset switch. Which one is it?

[@AmreSupply]

Hi Ho Kim, Most limit switches will be an auto reset but check your switch first. If your switch has a button on it then it is a manual reset. If there is no button then it is an automatic reset. Hope this helps!

[@Tombabahoto]

hi, thank you for the info, Im trying to find limit switch for my Lennox furnace, are they all the same? or there is specific switch for specific model, thank you in advance

[@AmreSupply]

Thanks for watching. Limit switches will differ based on the physical shape and size and where the mounting holes are located. Switches will also differ based on the temperature ratings. The switches will list a Cut out & and a cut in temperature or the side of the switch will have a rating that looks something like this: L150-40F www.amresupply.com/part/16687695 Which means it will cut power when the temperature reaches 150°F and cut in when the temperature is 110°F (40 degrees less). So you'll have to match these specs for the switch of the same size and shape to work properly in your furnace.

[@weiyu5335]

Thank you for the helpful video! I am wondering if you know why the fan to my furnace will immediately turn on and off twice (only for a few seconds) after a heating cycle. Could this be due to a problem with the safety switch?

[@AmreSupply]

Thanks for watching. It could be because of one of the safety switches potentially a pressure switch. It would be best to observe and see if the furnace gives any error codes. As well some of the logic is shown in this video kzbin.info/www/bejne/mGHWcnqqYpahn7c

[@tonymejia2497]

To limit switches have a part number on them so you can replace them with the correct part

[@AmreSupply]

Thanks for watching. There are several ways one could find a new limit switch. You could look up the model number of the furnace and sometimes you might be able to find a parts diagram. Some switches will have a part number so you can find a match that way. If needed you can match by physical dimensions and the rating. If a switch says L170-40 it means the switch will open at 170°F, and close at 130°F

[@taozhang9523]

That is clear and helpful one!

[@AmreSupply]

Thanks Tao!

[@angesomt4641]

thank you for your help

[@AmreSupply]

You're welcome!

[@johnhouze9592]

Furnace runs blowout heat but not like it did last year. ICP# N8MSL..led code light flashing like heart beat.

[@AmreSupply]

Thanks for watching. There is likely a chart showing what the error codes mean. This might be listed on a sticker on the inside of the furnace door, or in the in the furnace manual.

[@ramblinman7153]

So my limit switch keeps tripping. I used a multimeter to verify that it reads 24v when it trips. I also tested continuity and it was good. I removed the limit switch and used a jumper to keep the furnace running while using a meat thermometer to check temperature in the port. Temperature never came close to the 200F specified on the limit switch. So I replaced the limit switch and it's still tripping. Air filter brand new and still trips if removed. Blower is 1 year old, furnace 6 years old. All registers are open and should be clean. Unfinished basement so only registers on upper levels. No kids or pets that might stuff something in the registers. There are no dampers either. AC unit was replaced last summer, so the coil should be relatively clean. What else could it be? Evey time a tech comes out, they suggest something different with a huge expense. Kind of like going to a jiffy lube and being up sold a cabin air filter replacement for 75 bucks. Moreover, it never locks out on me. And I only seem to have the issue when bringing the house to temperature in the morning. Say from 65 to 70. It runs fine during the day and night to keep things at temperature.

[@AmreSupply]

Thank you for watching. It seems like you've done everything you can eliminate a defective limit switch as the source of the problem. You have likely done this but its always best to check all wire connections to make sure there is no corrosion and also check that the wire terminals are secure. The fact that it only trips in the morning is strange. In that case the furnace would likely be running for longer, and might get hotter than when the furnace is running during the day. Perhaps check to see what the temperature of the port is in the morning compared to when you checked. Does the furnace give you any error codes?

[@ramblinman7153]

@@AmreSupply I will definitely check the port in the morning. But I assume you are right that it runs longer or long enough to trip the switch. The furnace error code is 4 blinks, which per the furnace manual is Limit Circuit Open.

[@ramblinman7153]

I've now checked evap coil and it's clean as a whistle as are blower and wheel. Temp rise test is well within specs. I've set the temperature up about ten degrees so I can see what happens. It's tripping almost exactly every ten minutes.. Blower will then run for two minutes before the furnace ignites again. I don't see any rust nor corrosion on anything.

[@AmreSupply]

@@ramblinman7153 Thanks for the update. These sorts of things can be tricky to narrow down. You mentioned that you previously bypassed the switch. In that case if the furnace runs well without shutting down, then you know that its the limit switch that is the problem. If your bypass test still resulted in a shutdown then you'll know its an issue with the control board. Control boards have lots of small components and capacitors that can't be easily tested like the limit switch so its difficult to completely narrow down. The board itself is easy to replace though.

[@jhill7974]

Will a faulty limit switch keep the blower running during summer months using AC ?

[@AmreSupply]

Thanks for watching. It depends on the model but yes a faulty limit switch can keep the blower fan running longer than what is necessary. It depends if its a fan limit switch or a high limit switch, which will be wired differently in the circuit. Its best to check your wall thermostat fan settings first before testing or replacing the limit switch.

[@richardkendallmd3486]

"ROLLOUT SWITCH" AND "HIGH LIMIT SWITCH" LOOK VERY SIMILAR ON MY FURNACE. HIGH LIMIT SWITCH WAS BELOW THE COMBUSTION CHAMBER, ROLLOUT SWITCH WAS ON THE SIDE OF COMBUSTION CHAMBER.

[@AmreSupply]

Thanks for watching. You are right that they can be similar. As a rule of thumb the flame rollout switch will always be closer to the burners

[@Rob-Mc]

Thank you Dad I never had. 😁😂😢😭

[@AmreSupply]

You're welcome, we're glad you found the video helpful!

[@ryanjohnson1641]

Does this work the same for an electric furnace?

[@AmreSupply]

Thanks for watching. Electric furnaces also have limit switches that will shut off the furnace if the temperature gets too high. The ratings of the switches will be different between models but the principles are the same.

[@nycdidar]

My furnace has 7 blinking led indicating lockout for retry. Furnace works on fan ON mode. But If I set to fan AUTO then it ignites few time. I see the flame. But blower does not kick in at all. Hence furnace shuts down after trying few times. I tried cleaning flame sensor. No luck.

[@AmreSupply]

If your furnace works on Fan ON mode not during Fan Auto then it could be a couple issues. If your furnace uses a multi-speed motor, or if your furnace also has an AC unit, then your blower fan motor could be faulty (the windings on one of the speeds could be shorted or burnt out) Alternatively there could be an issue with the control board, but this is best tested by a professional. As for the limit switch, generally this will give you a specific code if the limit switch is open, so its likely not the issue but you can still test it to make sure. Hope this helps.

[@loveandhappy8673]

Hi. Vance. I am wondering if I can buy any limit switch for my special furnace. Do you think all limit switches are interchangeable? thank you.

[@AmreSupply]

Hi Paul, thank you for watching. As long as you match the size and the temperature rating then you can use any limit switch that matches. For example a L150-20F switch will open at 150°F and close again 20° lower. Some switches will just list a temperature range 130-150F etc You can order limit switches here: www.amresupply.com/catalog/Fan-Limit-Controls-HZ3D

[@verlonrackey1820]

My limit switch is cracked and the wire looks burned I’m thinking this isn’t good at all. What may be the problems? I’m forsure going to replace the limit switch and wire that looks burnt.

[@AmreSupply]

Hi Verlon, when the limit switch fails then the furnace will think that the heat exchanger is overheating. Generally the furnace will ignite, the blower fan will run and the furnace will shut off before it gets a chance to heat up.

[@steveneldred8928]

Does it matter which way the new limit switch goes in? The one that's in the furnace now is marked with a green dot on one wing matching a green dot on the housing. Also, the multimeter shows .04; I assume that means it's faulty.

[@AmreSupply]

Hi Steven, thank you for watching. Its always best to replace the limit switch in the same alignment and orientation as the previous switch so that the switch is responding to the same path of air over the heat exchanger. As for the multimeter reading, 0.04 ohms is continuity, as there is still a continuous electrical path present in the switch. Limit switches simply provide a path for the electricity to pass through and will generally have a resistance between 0 - 1 ohm. Testing the switch at room temperature will tell you if the switch has failed outright but will not tell you if the switch is opening correctly at its rated temperature. That is difficult to test, so in a lot of cases its best to replace the limit switch to remove it as a potential issue.

[@tonyschol4326]

Would the limit switch do the same thing and start and shut off the exhaust fan even in the summer with the central air unit running?

[@AmreSupply]

Hi Tony, thank you for watching. It really depends on the wiring. If the limit switch is wired into the blower fan circuit then a faulty switch cancreate problems with the central air conditioning running. Regardless most common causes of an AC unit cycling on and off is a dirty compressor that is overheating, poor airflow over top of the evaporator coils (dirty furnace air filter), or issues with your thermostat.

[@tonyschol4326]

AMRE Supply the central air unit isn’t shutting off it’s just the exhaust fan that is running for like 7-10 seconds then off of 7-10 them back on. The blower doesn’t do the same it runs and cools just fine.

[@AmreSupply]

@@tonyschol4326 Some furnaces have blower fans controlled by fan limiters, and other models have just a high limit safety switch. In your case it does seem like you have a faulty fan limiter.

[@tonyschol4326]

AMRE Supply thank you!!! Much appreciated

[@AmreSupply]

@@tonyschol4326 You're welcome Tony!

[@yangyangs34]

will a limit switch cause the ac not to come on? my board beeps 4 times indicating a limit switch. blower motor will come on for about 5 minutes the shut off. condenser wont come on

[@AmreSupply]

Thanks for watching. Yes in some models a limit switch act as a broad safety switch even while the AC. If the limit is faulty then the system might think that it is overheating during an AC cycle.

[@leonardlewis5586]

Vance looks like the jolly Rogers of hvac

[@AmreSupply]

Thanks for watching.

[@peterburkey3740]

Where do you get furnace parts like this limit switch?

[@AmreSupply]

Thanks for watching. You can order online or come to one of the 12 AMRE locations to get furnace parts like these. www.amresupply.com/catalog/650036

[@verizoncustomer1600]

Hi Vance . . . i have a question for you . . . I have a Dayton Gas Furnace which looks exactly like yours in the video - same switch location - when I test the Limit Switch on my Cen- tech Digital Multimeter it reads 2.3 - That in turn is a bad switch correct ? Otherwise the multimeter would have had the same screen it showed me when I turned it on right ( if the switch was good ) ? The Multimeter was in the lowest ohms setting ( 200 ) .

[@AmreSupply]

Thanks for watching. When testing the limit switch it should have continuity with a resistance between 0 and 1 ohms. A resistance of 2.3 is still pretty low and shouldn't affect the operation of the switch. Now if the switch has failed completely, then there will be no path for electricity to pass through, and no resistance at all. In this case the multimeter will be blank, or will show OL (open loop).

[@verizoncustomer1600]

@@AmreSupply Ahh . . . I wondered what the OL stood for - the Multimeter read 1 and then a open space where 4 or 5 digits would have been then a dot - then when the probes were put on the limit switch it read 2.3 - I re- inserted the switch in the Furnace hooked the wires back up - took out the filter ( yes it was dirty ) and flipped the power back on and so far it has been running perfectly - Thank you for the great video . . . and taking the time to get back to me . . . going to get a new filter . . .

[@AmreSupply]

@@verizoncustomer1600 Its definitely good to regularly replace the filter. We're glad that you found the video helpful, we're just happy to help in what small way we can! Cheers!

[@DT-nr6ev]

Should the limit switch contact the combustion chamber or just measure the air temperature. I have a thermal switch that keeps tripping but it is actually hitting the combustion chamber so much so that it is making a slight dent in the switch. I'm wondering if my installation is incorrect.

[@AmreSupply]

Hi Dave, most limit switches will monitor the air temperature or the air that travels over the heat exchanger. The heat exchanger will be much hotter than the air, so if the switch is making contact then it would cause it to trip more often. If you have an older furnace, there might be 2 limit switches, one for the high limit and one for the fan. The fan limit delays the blower fan from running until the air is warm enough. Newer furnaces just use a time delay. Its unlikely but some fan switches might be positioned closer to the heat exchanger, it depends on the model. There is a lot of variety.

[@scottlarson6699]

Great video! I have a Heil NDGK075DF03 that stop running the burners after awhile & won't turn relight for a couple hours of being off. I pulled the limit switch & all it has is a part ELMWOOD #2455R but no temp. range. How do I find out the range? Bought one online ELMWOOD-2455R F194 Close 194F that I'm guessing is open because it has no continuity, I think that's what the "F" is for instead of "L" which is probably what I need. Any help would be appreciated.

[@AmreSupply]

Hi Scott, thank you for watching. Unless there is something unique about your furnace your limit switch should be closed and have continuity at room temperature, it opens at its high limit and closes at another range as well. Both numbers need to be taken into account. If you tested the limit switch in your furnace and verified that it has no continuity at room temperature then its best to install a new one. If you're not sure if the limit switch is the problem then its best to try to check the furnace codes or narrow down the part based on these steps in this video: kzbin.info/www/bejne/mGHWcnqqYpahn7c If possible try to use your model number of your furnace to get more information on the temperature range of the switch. If you're able to find a parts list will likely list something like SWITCH LMT 130-20 or even something like SWITCH LIMIT 170F-30 etc In this example 170 °F would be the temperature it opens and it would close 30 degrees below that at 140 °F Hope this helps.

[@scottlarson6699]

@@AmreSupply I'm pretty sure this 80's furnace doesn't have any codes or lights to check or run. However, I was able to check both limit switches (1 near burners, 1 on draft/exhaust housing) that were closed (continuity) at the time the furnace wasn't firing so I believe they are ok unless they're intermittent. I'll check the video you linked & try to further diagnose. Thank you.

[@AmreSupply]

@@scottlarson6699 It if is an older furnace with a draft inducer, then you might have a fan limit switch. This is different than a high limit switch in that its used to help control the blowers. The blower isn't supposed to turn on right away so without an intellegent control board, the switches are used. In this example a fan limit switch would be open at room temperature and would only close (and turn on the blower) once the heat exchanger warms up. Its important to narrow this down as putting the wrong limit switch will cause the furnace not to work correct. More info on fan limit switches is here, if you scroll down there's a section on the sequence of operation: inspectapedia.com/heat/Fan_Limit_Switch_Guide.php

[@chexsecakee1612]

Hello we need to fix the limit switch for our furnace but we can’t find our exact model(l200f 30), could we use a similar limit switch instead? For example could we use the l250 40 instead of the l200 30?

[@AmreSupply]

Thank you for watching. Your furnace is designed to operate with that specific limit switch and it is not recommended to put a different switch in as it will change how the furnace operates. Those number refer to temperature limits and the temperature difference that it closes at. Those ratings need to be exactly the same.

[@Okikor1]

If it trips the high limit switch will it also cut power to the WiFi thermostat (no batteries)? When it happens, there's no voltage between R and C for about 45 seconds. What could it be?

[@AmreSupply]

Hi Okan Korsal, when the limit switch trips, generally the blower fan will continue to run to help cool down system and some furnaces will also cut power (24V) to the thermostat before it restarts.

[@tammyrogers3149]

Older model floor furnace 5088-2 that will not stay lit?

[@AmreSupply]

Thanks for watching. If the model uses a pilot flame then you can test the thermocouple or thermopile voltage to see if the pilot flame is heating up correctly. We have tutorials for DC voltage tests with water heaters but the same tests can be done with a furnace. For a model with a therocouple you can follow the steps here: kzbin.info/www/bejne/gqaYeKmYq9ijg9k For thermopiles: kzbin.info/www/bejne/i4nTnqB9qsqqoZo

[@guillerminaguzman4685]

Can a faulty limit switch cause air to be lukewarm instead of hot?

[@AmreSupply]

Thanks for watching. A faulty fan limit switch in some furnaces might change the perceived temperature. Generally air coming out of the vents is not extremely hot as it cools slightly when traveling through the air ducts. Is it no heating up to the right temperature anymore or does your home still heat properly?

[@guillerminaguzman4685]

It's not heating up as years prior. When I pass by the vents the air seems a lot cooler than it should be.

[@russellcrea9701]

My 5 year old Bryant furnace recently started short cycling and not getting up to temperature even with a new filter, but if the filter is removed it works fine. I suspect the limit switch, it's L170-20F. Does this sound like the problem and does the replacement have to be the same specs or how close does it have to be and would there be an advantage to using one with slightly different specs? Any help is appreciated - Thanks.

[@AmreSupply]

Hi Russell, thank you for watching. Its always best to replace the switch by matching the numbers exactly. These switches are used as a safety, so a different temperature cutoff is unsafe to use. The numbers refer to the temperature that the switch will open and disconnect power, and the 2nd number refers to the difference in °F that the switch will close again.

[@russellcrea9701]

@@AmreSupply Thanks for the info. I will only try to replace it with one of the same specifications.

[@AmreSupply]

@@russellcrea9701 You're welcome!

[@elcarlstono]

Does the wire order matter, when reconnecting the switch?

[@AmreSupply]

Thanks for watching. Switches and fuses are simply paths for electricity to pass through and aren't affected by the polarity of the wires. This means it doesn't matter what order that you reconnect the two original wires, the switch will work the same.

[@elcarlstono]

@@AmreSupply thanks!

[@christopherfisher123]

I have a Gmp075-4 Goodman furnace and I have checked all the switches. I just replaced circuit board about two years ago along with blower motor. The other night I turn the unit on and the igniter lights up the flames come on the draft motor spins and the blower motor will cut on after a minute but will not blow the air through the house. When I turn the thermostat from Auto to ON the igniter will light up the flame comes on etc. but as soon as the igniters lights the flames in the ON position on the thermostat the flames automatically go out but it does blow air through the house when The thermostat is set to ON.anything you can suggest?

[@AmreSupply]

Thanks for watching. The "On" setting for the fan means that it will ignite the burner, heat and run the blower, and then when the heat is off, the blower fan will continue to run 100% of the time. The "Auto" setting means that the blower fan only runs when heat is needed. Based on what you wrote, on both settings, the heat is cut after the burners are igniting implies that the limit switch is tripping. If there is poor airflow or a dirty filter, then the heat exhanger might be overheating and tripping the limit switch. Alternatively the limit switch might just be wearing out. It uses a small bi-metallic disc inside that can warp over time. This can cause the limit switch to trip at perfect safe temperatures, shutting off the heat prematurely.

[@joeydelmarsjr.646]

my heater kept cycling the flames every 5mins or so, i thought it was the pressure switch but the hvac tech said going from a 3.5 to 4ton might be the issue so he plugged up one of the burners and moved the ignitor over one. now the furnace wont over heat as he put it but doesn't that make it take longer to heat the house? its a rheem 801T x13 100k @ 80% code was 22.

[@AmreSupply]

Thanks for watching. If the furnace was overheating and was tripping the limit switch then closing off one of the burners would solve that problem. It might take longer to heat the home initially. You'll likely notice the furnace staying on slightly longer than it did before, or it might cycle on a little more frequently. Shouldn't make a massive difference though.

[@joeydelmarsjr.646]

@@AmreSupply thank you for taking the time to reply to my question after he plugged up one of the burner inlets I no longer have the overheating issue or tripping of the Furnace my question now is is it okay to go from a medium low to a medium speed tap or it really should or would not make a difference of only 200 cfm. Basically I went from a PSC to a x13 and I'm trying to match the cfms from the previous system to the new system. The old system was 100k 80% Quattro psc 1/2hp heat was med and cool was hi spd tap. Roughly heat 1400cfm and cool 1600cfm @ rating .5wfc. This new sys is 100k 80% minus 1 burner derated 3/4 hp x13

[@AmreSupply]

@@joeydelmarsjr.646 There shouldn't be a huge issue going from medium low to the medium speed as its just pushing more air over the heat exhanger. The slight difference in speed might not affect the overall heating in a noticeable way. If the furnace turns cycles and heats like normal then you might not need to adjust it.

[@JasonSmith-qx3zh]

Would this be the same as the ones with a reset button on the top of them?

[@AmreSupply]

Hi Jason, thank you for watching. You are likely referring to the flame rollout switch. kzbin.info/www/bejne/aGSveIWolr6InZI

[@jasonwalsh3807]

Can you test the switch before removing it?

[@AmreSupply]

Hi Jason Walsh, in some cases you can test the switch before removing it but every setup is different and some are easier to access than others.

[@JR-gq8ti]

Can the wires be hooked up backwards?

[@AmreSupply]

Thanks for watching. A switch simply connects or disconnects power. Its not effected by the polarity of the wires so it doesn't matter which terminals the 2 wires are connected to. You can swap the order and it won't effect the switch.

[@edfletcher1716]

My problem is the furnace starts normally, induction motor comes on then igniter then the burners for a couple minutes then when its time for the fan to come of the flames go out. The induction fan stays on for a few minutes then shuts off. I have a red indicator blinking continuously. I know the fan works because I can turn it on manually and works fine with A/C. Any thoughts? I removed the flame sensor and cleaned it with no change.

[@AmreSupply]

Hi Ed, thank you for watching. The flame sensor could be faulty or the flame sensor not be in the right position which would prevent it from heating up and verifying that there's a flame. The tip of the flame sensor should sit just in the flames.

[@mariodilorenzo7473]

will the furnace fan be stuck on if this switch fails

[@AmreSupply]

Hi Mario Dilorenzo, when the Limit Switch fails, the furnace thinks that the system is overheating so the blower fan will continue to run to cool down the system. In most furnaces this will only go on for several minutes before the furnace shuts off and turns back on to try ignition again. In some cases the blower fan might run for longer. The other thing to check is your thermostat settings. If the fan is set to On it will run all the time. If its set to auto, the blower fan will only run when the furnace is providing heat.

[@chains7]

I have an old coleman 2865-656. The furnace is still working fine but what happens is it runs a normal cycle then shuts off. A few minutes later it will start blowing for about 10 seconds then shut off? Could this be the limit switch or any ideas what could be causing this? If I open the furnace door or remove the filter the short cycle does not happen

[@AmreSupply]

Thanks for watching. It could be a faulty limit switch cutting out at lower and lower temperatures. Since the symptoms improved when you remove the filter and opened the furnace door its worth checking to make sure that the airflow is good overall as this could cause the heat exchanger to overheat. On the other hand if you open the furnace door, heat will be released and its possible that the limit switch is just not getting near it's cutoff point anymore.

[@chains7]

@@AmreSupply Thanks for the reply. It looks like you don't sell the limit switch for my coleman model 2865-656. Do you have anything that is compatible?

[@AmreSupply]

@@chains7 If the part number doesn't come up as an exact match then you can match by shape and by the rating. You will likely have a number on the side of the limit switch. For example if the switch says L170-30F then that means the switch will open at it's upper limit of 170°F and close after the temperature has dropped 30°F below that limit (when it gets to 140°F). Knowing this can let you match with any switch with the same mounting holes and shape. www.amresupply.com/catalog/Fan-Limit-Controls-HZ3D

[@chains7]

@@AmreSupply Mine only is stamped with 195F ? Other markings say 205811, 2845-319 & 60T14. Furnace is coleman model 2865-656

[@AmreSupply]

@@chains7 Judging by the 60T14, that denotes a 60T series of switches. The 60T14 is the style. There is this document that is from Emerson: www.emerson.com/documents/commercial-residential/60t-product-bulletin-en-us-152042.pdf This shows a numbering guide. Looking at this other emerson document there is a part list: climate.emerson.com/documents/snap-disc-fixed-temperature-fan-limits-catalog-en-us-4282456.pdf Going by this and picking a slightly lower limit at 190 this part number 3L01-190 might be the closest match: www.amresupply.com/part/16687696 Hope this helps!

[@vietcong411]

When i set my multimeter to the lowest settting, 200 ohms, i get a reading of around 120. What does that mean?

[@AmreSupply]

Thanks for watching. The limit switch should not have resistance. It is a switch. When the switch is closed, there should be a unrestricted path for electricity with a resistance of 0 to 1 ohm. When the switch is open, there is no path for electricity to flow, so the multimeter will show - - - - - , or OL as there is no resistance reading, as the switch effectively has an air gap between the terminals. If your switch shows 120 ohms then it's faulty and should be replaced.

[@truth1always]

I have a coleman set up for down flo. The furnace burners lite but as soon as hear the click for the blower to come on, the flame cuts off at the exact same time. Would that be the limit switch?

[@AmreSupply]

Since your furnace goes through ignition but cuts out after the heat exchanger heats up then it does sound like its the limit switch. If you want to be completely sure then take a look to see if your furnace flashes any codes after the flame cuts out kzbin.info/www/bejne/mGHWcnqqYpahn7c These codes are unique to each model, your furnace manual or a reference chart on your furnace will let you know what the code means.

[@Geo-vg3xu]

What happened if I switch out my old style Honeywell switch with one of these?

[@AmreSupply]

Thanks for watching. When installing a limit switch it must be similar enough to be mounted in the same way and it must also have the same ratings. Without the same ratings, it will change how your furnace operates. This can make your furnace unsafe.

[@bbrady9673]

What if you have crappy wiring all one color and no indicators for what wire is which? what side of the switch gets positive and negative terminals?

[@AmreSupply]

Hi Beau, if you have a limit switch similar to the one in this video then the polarity of the switch doesn't matter, so you can swap the wires and the switch will still function as normal. In older furnaces that use an older style fan limit switch, reversing the polarity could damage the components of the switch. If needed a piece of tape can be used to remember which wire goes on what terminal.

[@wymi]

The current limit switch in our Heil furnace is an L150-20F. The replacement switches I see for sale are L150-30F and they say that is the upgraded replacement part for the switch we have in the furnace now. Will the L150-30F work okay in place of the L150-20f limit switch? What are the differences between those limit switches? Thanks.

[@AmreSupply]

Hi Wymi, L150-20F means the switch opens up and will turn the furnace off at 150°f and will close at 20° less (at 130°). Installing a L150-30F means that the switch will close at 120° (so 10° cooler than the other limit switch. Its best to put the exact same rating in as this is what the furnace is designed for but a 10° difference on the lower number won't affect the protection. These high limit switches are to protect the furnace when the temperature gets too high so the upper limit matters most. There are adjustable switches, that can be set assuming that is physically similar to the one that you need. To get a 150-20F you can use an adjustable switch with a 20F difference that can be adjusted to 150°F then you'll have an exact match for specs. www.amresupply.com/part/AT022-FAN-LIMIT-SWITCH-ADJUSTABLE-140F-180F

[@wymi]

@@AmreSupply Thanks for the info and fast response. The issue that led to the limit switch as a problem is the fan blower turning back on with in a minute of the system shutting down after the thermostat is satisfied. The fan only runs for about 10-15 seconds then shuts off. The filter is changed every 2 months w a low restriction pleated filter.

[@AmreSupply]

You're welcome Wymi. If you've eliminated the airflow as a source and the blower fan runs intermittently after the temperature has been reached, then that does point to the limit switch being faulty.

[@jayjeezy7156]

My dad connected the wires from my limit switch thermostat to a paper clip to keep the furnace blowing after 2 days the furnace shutdown the wires are burned and I'm getting no power at all what could it be

[@AmreSupply]

Hi Jay Jeezy. First of all, its never a good idea to "jump" or bypass any safety switch in the furnace. Each safety switches are there to ensure that the furnace is operating safely and the limit switch protects the furnace from overheating. In this situation there was likely a short circuit that caused the burned wires. Its best to call a HVAC technician to take a look at your furnace.

[@ramblinman7153]

Blown fuse on the control board.

[@pathoughton3247]

I have a coleman pilotless furnace..Blowing cold air.I checked my Filters, all clean.The furnace hums like it wants to click on but don't..Ideas??

[@AmreSupply]

Hi Pat, thank you for watching. Do the burners ignite? If so do the flames stay on and run for several minutes before the blower fan kicks on? Also does the furnace kick up any codes or blinking lights?

[@riwibela]

Hi, my furnace is Trane xr90. It keeps blowing cold air. I have replaced the filter and reset the furnace. The problem still exists. Do you think I have to replace the limit switch, or something else?

[@AmreSupply]

Hi Riwibela, it might seem simple but first double check that your Thermostat fan isn't set to On, (which will cause it to run the fan continuously). Make sure the fan is set to auto (which will only run when heating is needed). Many furnaces use flashing lights as codes, so if you see any flashing lights, look at your furnace manual to reference what they mean. (3 reds might mean _____ while 2 reds might mean something else) Its different for each model. This can help you narrow down what is wrong right away. In general, the limit switch can cause the furnace to cycle on and off. If it starts to fail it will start shutting the furnace off at lower and lower temperatures. The furnace will keep the blower fan running to make sure the heat exchanger doesn't overheat, which might make it seem like it is blowing cold air. If you remove and test the limit switch, and it has no continuity, then you'll know for sure to replace it, but for how common it is, it doesn't hurt putting a new limit switch in regardless. www.amresupply.com/catalog/Fan-Limit-Controls-HZ3D

[@riwibela]

@@AmreSupply Yes, the fan was set to auto mode. When I turn the thermostat to higher temperature, the furnace will be on with cold air only. I will test the limit switch and see if it is failure. Thank you.

[@samm928]

I whished he would go over of the switch types and ratings .. what is a snap disc, why some are NO and some NC .. what is L165-60F mean .. Anyone can replace a part something that looks similar, but what if the part is not available ? .. can I use a L175-40F instead ?

[@AmreSupply]

Thank you for watching. That is good feedback. In our newer videos for appliance repair we have tried to add in more detail about what specifications you'll need to look out for as well as what variation there is between models. We do however have a video explaining switches in general and the difference between NO and NC. kzbin.info/www/bejne/g5XYaISidt-Khck L165-60F means that the switch opens at 165°F and will close after dropping 60°F (at 105°). It is still always best to install a switch with the same high limit as this is what safe upper limit the furnace was designed with. There are older models that use fan limit switches which might have a NO and NC switch which cover a different range from each other. These are generally in models that have a more simplistic circuit board in them.

[@blueskyaircon3245]

what is the differance between limit switch and flame rollout switch .. they are a same shape

[@AmreSupply]

Thanks for watching. They are both thermal disc based switches but will be configured a little differently and will have different ratings. Some flame rollout switches have a reset button and some don't. Limit switches generally don't use a reset.

[@blueskyaircon3245]

@@AmreSupply Thank you so much for your imazing videos they was so helpful

[@AmreSupply]

@@blueskyaircon3245 You're welcome, we're just happy to help!

[@patrickallen4120]

What housing ? So distinct a noise

[@candacerushing6882]

My thermostat seems to be functioning normally. It calls for heat, the furnace comes on and heats the house. When it reaches temperature, the thermostat “clicks,” telling the furnace to shut down. The blower continues to run for a few minutes until the air is cool. Then, the blower fan shuts off. A few seconds later, it comes back on for 3-20 seconds. Shuts off. Comes on. This happens 6 or more times, finally, I hear a “click” at the furnace and it stays off. Is the fan limit switch going out? Thanks! (Duo-Therm Furnace in an older mobile home)

[@AmreSupply]

Thanks for watching. Since the furnace reaches its temperature before it shuts off and starts cycling on and is a sign of a faulty limit switch. The switch has likely worn out and is tripping at lower and lower temperatures.

[@candacerushing6882]

@@AmreSupply Thank you SO much. 🙏 I will try to order the part from your website. Great video- very helpful!

[@AmreSupply]

@@candacerushing6882 You're welcome, we're just happy to help!

[@candacerushing6882]

@@AmreSupply Sorry to be a pest. I’m not having much luck with your website. The part I need is a Therm-O-Disc switch that says AF 151 F130 47100 6 74 on the side. I’m not really sure what the actual “part number” is. It’s for a Duo-Therm furnace (76601-001) in a 1976 mobile home. I have photos. I found ONE place that sells Duo-Therm parts, but they only sell to contractors. Thanks for ANY suggestions!

[@AmreSupply]

@@candacerushing6882 It is hard to find parts for older furnaces, and I'm not sure how many specific parts we have for mobile homes compared to residential homes. If no part number show up when you search you can match based on shape and rating. You will see that these switches have a cutoff temperature which from your example is (F130) or 130°F. There can also be another number of when it cuts in again. www.amresupply.com/catalog/Fan-Limit-Controls-HZ3D It is however best to find an exact replacement by the part numbers themselves but can be tricky to narrow down. If you have the same shape and size, and temperature ratings then the switch will work the same regardless of brand.

[@chrislawson6509]

When i turn on my furnace it will light and turn on but the blower will shut off after a minute. Could the limit switch be the problem?

[@AmreSupply]

Hi Chris, thank you for watching. What you are describing is short cycling, and the fact that it lights, blower fan runs then it shuts off does point to the limit switch. A full explanation of short cycling is covered in this video: kzbin.info/www/bejne/mGHWcnqqYpahn7c

[@RahulRathi_Multimedia]

My gas furnace had been short cycling for a few days now. Since this morning upper zone is not working, although lower zone is working just fine, and no short cycling either. I have checked the thermostat, also tried to bypass the thermostat, the damper motor seems to be working too (opens when furnace is turned off and closes when lower thermostat is turned on, but it won't open when upper thermostat is turned on). Could it be a faulty Limit switch? If not, any idea what it could be?

[@AmreSupply]

Hi Rahul, thank you for watching. Overall its best to see if your furnace gives you any error codes after it short cycles. This can help you narrow down the problem. We also made a video that focuses on short cycling as depending on where in the sequence it happens will help you know which part is faulty. kzbin.info/www/bejne/mGHWcnqqYpahn7c If the furnace heats up normally and then shuts off after blowing hot air then the limit switch might be faulty or it the air temperature inside the furnace is too warm. In this case it would be best to replace the air filter, and test the limit switch for continuity.

[@RahulRathi_Multimedia]

@@AmreSupply Thanks for your response. The furnace runs fine most of the time, but often shuts off before reaching the target temp. Then the fan short cycles several times with no flame. After like 4 times doing that within a minute or two, the flames light up and then it runs just fine. Looks like a limit switch right? I checked your other video, thanks!

[@AmreSupply]

@@RahulRathi_Multimedia If you've replaced the furnace filter and the airflow around the heat exchanger is good, then it does point to an intermittent problem with the limit switch.

[@RahulRathi_Multimedia]

@@AmreSupply thanks so much !! I'll order a new limit switch and see how it goes.

[@robertmcclung8035]

My fan keeps running after it stops calling for heat so i'm assuming its the limit switch. I open my total electric (Coleman)furnace and see what appears to be 4 limit switches in a row. Does this sound right?.... Are they all 4 limit switches? they look identical to me. And if they are all the same.... should I even take the time testing them individually? ,,, or just replace them all. Seems fairly inexpensive at 10-12 dollars a piece.

[@AmreSupply]

Hi Robert, multistage furnaces use more than one limit switches to monitor different temperature ranges, so its possible that all 4 are limit switches. It doesn't take long to test them individually just to get a sense.

[@robertmcclung8035]

@@AmreSupply Ok... Thanks for your reply

[@AmreSupply]

One more thing, when you take a look at the limit switches, take note of the temperature ratings listed on the side of the switches as this will indicate different temperatures. If you end up replacing the switches, make sure that you match the rated numbers.

[@robertmcclung8035]

@@AmreSupply great advice.... Thanx a million

[@AmreSupply]

You're welcome Robert! Cheers

[@ChitoWorld]

My limit switch reads L145-35F can I replace it with any? Amazon don't carry this one they carry L225-50 I feel this is not safe. I have a Coleman deluxe blend air II system . I keep trying to turn on the heat . Fire comes on than cuts off. At first the heater was turning down by itself now it tries to turn on for about a minute than it just shuts off. Sometimes I get fire lit but instantly goes out. . I feel is this limit switch. So is it safe to get any kind?

[@AmreSupply]

Hi raiders2800, if the furnace shuts off instantly after lighting, it could be the flame sensor which can either be cleaned or replaced as well. Its worth taking a look at our troubleshooting guide here kzbin.info/www/bejne/p4PQf6Wjn7B4r80 As for limit switches, its important to match the temperature ratings. L145-35F means the switch opens up and will turn the furnace off at 145°f and will close at 35° less (at 110°). A L225-50 would not be safe for your furnace as the switch opens at 225°. When searching, try to enter any other part numbers written on the side as you might have better luck finding a exact replacement. The replacement might not be a Coleman branded limit switch. Many furnaces will have a mix of parts from different manufactures. www.amresupply.com/catalog/Fan-Limit-Controls-HZ3D Hope this helps.

[@jeremyjjet4909]

I think I have too much gas getting by when I look at my flames it is coming out of more than just the port it’s coming out of the whole end and is getting too hot. There is an adjustment screw on my gas valve can I just turn it down to where it looks like it’s working properly

[@AmreSupply]

Thanks for watching. That is a good question and yes the adjustment screw can be used to adjust the size of the flame. Just be observant if its a crisp blue flame or if its yellow or golden. If the flame is yellow then it would also be best to clean the burners.

[@jeremyjjet4909]

I think I’m going to have to replace the exhaust fan also

[@AmreSupply]

@@jeremyjjet4909 The repair isn't too difficult we made a video outlining how to remove the blower wheel and replace the motor and capacitor. You can see it here: kzbin.info/www/bejne/aoS8aZ-IoZ17jJI Alternatively if you were referring to the inducer blower fan, then the repair is a little different: kzbin.info/www/bejne/e6StmZl8gr-KgKM

[@HungNguyen-sb1yu]

Does the limit switch have polarity?

[@AmreSupply]

Thanks for watching. That is a good question. It doesn't have any polarity as it simply connects or disconnects power to the circuit. It doesn't matter which of the two wires are connected to which terminal.

[@HungNguyen-sb1yu]

@@AmreSupply Thank you.

[@HungNguyen-sb1yu]

@@AmreSupply Thank you. If the flame rollout switch is bad, will burners light up?

[@AmreSupply]

@@HungNguyen-sb1yu The flame rollout switch shuts off the gas supply if the flames come out the front of the burners. A faulty switch will prevent the burners from working. If the burners are not lighting then it could still be an issue with the ignitor. This video helps explain the startup sequence: kzbin.info/www/bejne/mGHWcnqqYpahn7c

[@ATappin]

My limit switch is saying 1.1 when I test it. It's a 6 year old furnace and not lighting. I can see the ignition heating up but no flames after it clicks :/

[@AmreSupply]

Hi Alex, thank you for watching. The 1.1 ohms means that the limit switch has continuity so its likely not the problem. If your inducer blower works, the ignitor heats up and the flames don't light, then its most likely an issue with the gas supply. First check to see if the gas shut off valve is opened. Alternatively it could be an issue with the gas control valve as it needs to open to release gas for the furnace to ignite.

[@rmorelos7]

Why my high limit switch keeps on breaking ?I already replace it 3 times even the I also replace my filter. Please advise....thanks

[@AmreSupply]

Thanks for watching. If the limit switch keeps on failing then its likely that the heat exchange is running hotter than it should be. Dirty burners can cause issues. As well a deep cleaning of the furnace and the vents could help as anything that restricts the airflow can cause the temperature to rise. In this case it might be best to hire a professional to take a look.

[@tetos1454]

Ok . What about if the switch is good ? I already test it , the switch is good and the problem continues .

[@AmreSupply]

Hi Teto, if your furnace continues to cycle on and off then its worth watching this video, as it covers some of the other safety switches that could be tripping kzbin.info/www/bejne/mGHWcnqqYpahn7c Also we just release a few new videos on troubleshooting specific problems. Hopefully one of the videos helps: Furnace Won't Start - Troubleshooting kzbin.info/www/bejne/eJqaZ6Rmid-ijZo Furnace Blows Cold Air - Troubleshooting kzbin.info/www/bejne/jqPbh2l_bahnr7s Furnace is Really Noisy - Troubleshooting kzbin.info/www/bejne/jZyrmJiKfrmcpac

[@Emillthe111]

Is this danger to have the water heater close to the furnace this pressure Val the vent gets hot will it get to hot causing the water heater to explode this is my dad house and I was wondering is this common to have it that close to the water heater

[@AmreSupply]

Furnaces and water heaters are often placed side by side or relatively close to each other. When installed urnaces and water heaters must meet several requirements. -Overall all gas-fired appliances shall be provided with outside combustion air. -The hot water heater must be able to be removed with the furnace completely intact. -The furnace room or closet must have a door large enough to remove the largest piece of equipment. - The access/ control side of the furnace must be unobstructed and should be accessible for maintenance. Generally the proximity of the furnace and water heater won't affect the operation. As long as either appliance is installed correctly, and the safety switches are operating, then everything should be running normally.

[@kennyd9257]

My furnace runs but shows a fault code of limit circuit fault...what could be the problem.?

[@AmreSupply]

Hi Kenny, thanks for watching. If your furnace gets a limit fault code then it could be an airflow issue creating overheating or the limit switch could be defective.

[@serenalunara7533]

so, what happens if the limit switch shows continuity, but the readout os .08 to .11 instead of 0.00

[@AmreSupply]

Hi Serena, thank you for watching. A limit switch is simply a path for the electricity to pass through, it will generally have a resistance between 0 - 1 ohms (a path with very little restriction to the flow of current) If the limit switch is faulty there will be no path for electricity to flow through. This will not show a resistance reading, the multimeter will show "- - - - - - -" , "OL" , or a blank screen. So your reading of 0.11 is a perfectly acceptable resistance for a limit switch.

[@bernardinopineda2614]

My furnace works great through 4 cycles but after i get 4 blinking lights and takes a long time to turn on again unless i turn of the thermostat for 10 sec and then turn back on could this be the limit switch??? Please help me

[@AmreSupply]

HI Bernadino, overall its best to check your furnace codes. They are written on the back of your blower cover door, or are sometimes in the furnace manual. This will tell you what those blinking lights means for your particular model. If the code comes back as the limit switch error then its still worth it to check the airflow and replace the furnace filter. If not then replace the limit switch.

[@jonathanblock9127]

The multimeter reading on my limit Switch reads 00.1. Is that considered 0?

[@AmreSupply]

Hi Jonathan, thank you for watching. Yes 0.01 that is close to 0 but overall switches will have a resistance between 0 and 1 ohm as they merely provide a path for electricity.

[@jungleviper]

Fsn linit switch is showing around 2 ohms

[@AmreSupply]

Thanks for watching. That is an acceptable resistance. Usually it's between 0 - 1 ohms as a switch is just a pathway for electricity to pass through. 2 ohms shouldn't change how it functions, it could just be dirty etc

[@pgg2061]

My thermstat's reboots and checked online and the cause seems to be the limit switch, the tech who had come to check says there is orange flame instead of blue and could not find out the fix, is this also caused by limit switch or is the issue something different

[@AmreSupply]

Thanks for watching. An orange flame will happen when it is not receiving enough air for complete combustion. This can be because of a plugged orifice or a dirty burner. If the furnace starts and stops after the flames are lit and after the blower fan is on, then it could be a faulty limit switch. If the furnace shuts off any other part of the sequence then it might be a different switch. You can learn more here: kzbin.info/www/bejne/mGHWcnqqYpahn7c

[@pgg2061]

@@AmreSupply Thank you

[@pgg2061]

@@AmreSupply Two Tech from different company came and confirmed there is Carbon monoxide leakage, i wanted a quote for a new furnace from a third company for comparison and the third tech who came cleaned the burners and checked the carbon monoxide levels too showed pic the flames are blue, and said there is no issue now totally confused.

[@AmreSupply]

@@pgg2061 carbon monoxide is produced when there isn't enough oxygen for compete combustion, so a yellow flame can produce higher CO levels. Regardless you should have a CO detector close to the furnace as a safety. One other factor that can cause the furnace to not run well is a blocked exhaust exhaust vent. Sometimes ice or a build up of leaves or other debris can restrict the airflow. On furnaces with inducers motors, the pressure switch should trip when this happens.

[@pgg2061]

@@AmreSupply Thank you for your reply. I order some extra CO alarm

[@okidokidiego5783]

Wath does mind the color drop on limit swich?

[@AmreSupply]

Thanks for watching. I am not sure what you are asking. Can you rephrase your question,?

[@robertrandall9564]

My furnace has 4 blinking red says limit switch open ..I replaced the limit switch then fired up the unit it ran for about 3 min.then shut down again after while it started to blink 11 red blinks saying limit switch open blower failure what do I do now..thank you

[@AmreSupply]

Hi Robert, thank you for watching. By replacing the limit switch you have eliminated that as a problem so if the limit switch trips its because of poor airflow over the heat exchanger. This can be caused by a dirty furnace filter, clogged ducting or by a weak or failed blower fan motor. Did the blower fan run during those 3 min? If not then the motor might have failed, the motor capacitor might be bad or the bearings might have seized. You can see how to access the blower fan, test the capacitor and replace the motor all in this video: kzbin.info/www/bejne/aoS8aZ-IoZ17jJI Hope this helps!

[@pablogomez7519]

if it is bad would it keep the burner and igniter to turn on??

[@AmreSupply]

Hi Pablo, thank you for watching. Yes a bad limit switch can lockout the furnace and prevent it from running or igniting at all.

[@pablogomez7519]

@@AmreSupply I have continuity on the high limit switch. I'm in front of my furnace now scratching my head 🙁

[@pablogomez7519]

I was just watching some of ur videos that can help me with my problem lol.

[@pablogomez7519]

I checked the voltage to see if I'm getting 120 from the wires from the inducer to the board but nothing

[@AmreSupply]

@@pablogomez7519 If your furnace isn't starting at all then watch this video: kzbin.info/www/bejne/eJqaZ6Rmid-ijZo Now if the furnace has power then the best thing to do is to check your furnace codes. When a safety switch fails or is tripped the furnace will give you a status code through blinking LED lights. kzbin.info/www/bejne/mGHWcnqqYpahn7c

[@dakotak8437]

Iv had all my limit switchs replaced and evertime my furnace shuts down my fan keeps running untill you shut of the breaker to reset it any suggestions

[@AmreSupply]

Thanks for watching. This means one of the safety switches has tripped. You could try to see what error codes your furnace gives you. As well start up the furnace and observe exactly where in the sequence it shuts off. This can help you narrow down the source of the problem: kzbin.info/www/bejne/rWbaZYSDmKiBi68

[@dakotak8437]

@@AmreSupply it never shows any error cods it always shit off at the burner one and it's been replaced sever times

[@AmreSupply]

If the burner ignites and the flames stay lit and the system shuts off after a minute of running, then it could be an issue with the airflow, the air filter, the limit switch or the control board. If the burners ignite, and the flames shut of a few seconds after startup then it's likely a dirty flame sensor. As well a dirty burner assembly can also prevent the flame sensor from working properly.

[@dakotak8437]

@@AmreSupply the flam stays on runs untill the heat gets warm in house the thermostat turns it off but the fan blower just stays on

[@AmreSupply]

@@dakotak8437 Check your thermostat Fan setting. Setting it to "On" will run the fan 100% of the time even when it is not heating. Setting it to "Auto" will turn on the fan only when heating is needed.