Gas furnace pressure switch code venting problems

This one talks about a gas furnace that is giving a pressure switch code. It concentrates on venting problems on the 90% efficient furnace. This video is part of the heating and cooling series of training videos made to accompany my websites: www.graycoolingman.com and www.grayfurnaceman.com to pass on what I have learned in many years of service and repair. If you have suggestions or comments they are welcome.
If you are a homeowner looking to repair your own appliance, understand that the voltages can be lethal, the fuels are highly flammable and high pressures are used. Know your limits.

[@tinoghebre2765]

I was about to pay 5,000 for a new furnace untill I saw ur video. The miracle words were " start wave in there....it doesn't take much" went up on the roof Lo and behold, water. Lifted up the pipe, now the furnace is working. Thank you.

[@grayfurnaceman]

Glad you got it going. GFM

[@orlandojohnson5742]

Very good information! When I was a younger tech we got call backs from things like this! It’s not always the pressure switch!! I’ve gotten birds out of draft inducer area many times on 80% furnaces too! If vent is hooked to a chimney you can guess a bird (dead afterwards of course) done flew in!! I had an older tech explain the pipers not slopped properly causing pressure switch problems! 90% furnaces are cool & great but honestly I like 80% better! More reliable to me in freezing temps! You don’t have drain issues in freezing weather with an 80%er ! When you get an emergency no heat on a 90% in below 32 degree temps you’ll understand what I mean!

[@percyfaith11]

Don't vent to outside, vent to waste drain pipe. No freezing.

[@Matthew_Jensen]

Thank you for the video. I ended up having two feet of snow clogging the pipe. Thanks for saving me a service call.

[@grayfurnaceman]

Welcome GFM

[@bradmironik6137]

Good diagnostic video. I installed many trane 90+ with their bay vent concentric adapter. Made for a clean finished product and keeps birds and other critters out. I agree you would still have to check for other debris. Thanks.

[@grayfurnaceman]

I have seen them where squirrels have gotten in. GFM

[@Honestandtruth007]

I just love the words you used to describe problems like some"craps here"..... and more......👍😅. But you very honest and very good instructor..... thank for Sharing...... God bless you and your family 🙏 😇

[@grayfurnaceman]

Thanks for the support. GFM

[@xsirfr1958]

Thanks! My Carrier was flashing "3-1" decoding to "LPS failing to close." Pulled the hose off and sucked on it - LPS clicks and closes. Next step, opened up the intake port, right before the inducer blower and found not one, but 2 unlucky birds had somehow gotten into the intake.

[@RobertWermuth]

THANK YOU I have been looking for this problem for 2 years

[@grayfurnaceman]

Welcome GFM

[@scottmagyar]

Great video sir, Question i have a Lennox Pulse 21 80,000 BTU and replaced it with a Carrier 2 stage Furnace 96% 80,000 BTU, can i use the pulse concentric 2 inch vent kit that's 2-inch pipe from furnace to concentric, mufflers are removed, or should i replace concentric with 3inch vent kit and 3 inch pipe, thks

[@grayfurnaceman]

The one sentence reply is: follow manufacturer's instructions.. GFM

[@sknight0391]

I pulled 5 bats out of an American Standard furnace last year, they were all the way down at the screen in the burner box. I found another dead giveaway that there is a blockage, is a lot of times you will hear what I would call a "wheezing sound." Kind of like a pregnant womans breathing technique in Lamaze class. Where the furnace is trying to suck air through every nook and cranny of the burner compartment. And the sure fired method for diagnosing a blockage in the intake is to just remove the burner compartment cover and let it pull air in from around its location. If the furnace fires and runs, you know the blockage is in the intake.

[@grayfurnaceman]

I don't know what it is with bats. I pulled 27 of them out of a camper furnace. 3 were still alive. GFM

[@JamesonSharp]

This is Fantastic Sir. Thank you.

[@mercifulservint]

@grayfurnaceman I have a trane xv80 and it's had a mind of its own. I have replaced the pressure switch and board in the matter of 2 years. It's randomly throwing this pressure switch code. It happens on cold nights and randomly whenever it does. I'm not sure where to look now. I've checked the flue, the top of chamber, wiring, etc. The replaced part stated are original trane parts. If you may have an idea where to look, I would greatly appreciate it sir.

[@grayfurnaceman]

The inducer fan may be your problem. Either the fitting on the inducer is plugged or the inducer is not coming up to speed. GFM

[@mercifulservint]

@@grayfurnaceman Thank you for your response. Everything is getting necessary power. I've narrowed it down to air flow somewhere. It's very intermittent. If I take the pressure hose off and put it back on without blowing or sucking, it fires right up. Also, how do I check to see the if there's a plug in there and speed of inducer motor?

[@ValiousTV]

Hello sir. I'm doing some D.I.Y. on my vents and could use a hand with a suggestion or two. A few years ago I got my first house and been doing renos. It's a 2 story and noticed the air flow (heating and cooling) was weird. Certain rooms got blasted with air and some got none. So I started tracing the vent lines in the basement (open ceiling) checking for dampers. In doing that, I found so many problems. It looks like someone in the 1980's did some D.I.Y. and it hasn't been touched sense. I'm talking holes in the venting, gaps on connections, multiple lines going nowhere (wall cavities)... and a layer of dust so thick it looked like a thin S.O.S pad. So I went to town, started cleaning the outside, vacuumed, washed, wiped. Then the gaps stated to show more. My vents honestly looked like a strainer. I cut a few square 'service holes' in the main line off the hood. To see inside, and get access to the branches from the inside. I've been removing the old connections (dead lines) and sealing the holes with a cut patch plate and that metal tape for vents. I started at the hood and air intake. Taping all connections, holes, every place that could leak air. Spent a few hours, making sure I got everything. The outside of my vent edges are shiny now. Just taping about 10 feet of the venting I've noticed a huge difference in air flow. So I'm planning to finish all I can reach. I've noticed in your video, you have a insulation wrap around your vents. Also your connections are taped. Really nice and clean looking. That's my goal also. What's that insulation wrap? I also want to wrap my heating vents after to reduce thermal exchange in the basement. I also don't like the idea of wires against the metal vents. I'd rather have an barrier between, I've seen some melting on the older wiring. I know that I'm bound to lose some percent of efficiency in the air. But if can get within 10% of maximum I'll be happy and saving on my bill.

[@antsara9218]

thank you! i had maybe 3/4 cup of water, drained it and Viola!

[@ravit6223]

Very effective troubleshooting steps 👍👌

[@brian3.2]

I saw that the venting had bushings in the 90's. This would most definitely hinder the return of the condensate water.

[@throttlebottle5906]

I like to use a cordless blower to check for pipe flow/obstruction and blow everything out.

[@kranch173]

I would have thought if the vent chart called for 2.5 in pipe as this install has. I would want as much of the 2.5in pipe as close to the furnace before adding the bushings or reducer if example it was 3in pipe

[@grayfurnaceman]

That install follows the manufacturer's instructions. GFM

[@harrydoherty8299]

had a pressure lamp flash code . the exhaust venting. had water twice . the pipe in the attic travels about 8 feet horizontally . i’m going to increase the angle toward the furness so water can’t get trapped in low spot .

[@MJ-iy4fb]

Thanks for the video. I was curious if both vent pipes need to slope toward the furnace? If one drains outside, in my case the intake does, is it a problem?

[@grayfurnaceman]

In most cases, they should. Manufacturer's instructions rule here. The problem with draining outside is the possibility of freezing at the termination. GFM

[@MJ-iy4fb]

@@grayfurnaceman Thank you.

[@bluzzedude8111]

Great video. I'm experiencing a red-3 blk, pause 3 blk pause..ect. I got up a 4 am and the furnace had stopped. I saw the 3 blk, pause pattern. I pulled some hoses off, sucked some sir, put them back on and turned the switch back on that sits on the furnace vent. Now, it's been working right for the last 8 hrs. However, this has been going on for quite some time. It works fine for wks, or longer, and then all of a sudden it stops. Most times it can be fixed just by turning the switch off and turning it back on again but I know it's only a matter of time before it goes out again...what do you think ? Thanks so much !

[@grayfurnaceman]

If its a Carrier, the 33 code should be overheat. I would be looking at the filter. GFM

[@irenecheca6575]

If they are sagging due to improper installation, is the installing company responsible & have to fix it?

[@grayfurnaceman]

yes GFM

[@driftlesstrekker4709]

I thought you're not supposed to use pressure elbows but rather DWV elbows?

[@grayfurnaceman]

Venting materials are determined by manufacturer instructions. In this case, the instructions indicate the use of this type of ells. GFM

[@mxbigd17]

Will switching from 2inch exhaust vent pvc pipes to 3inch exhaust pvc pipes help with pressure switch nuisance codes on the pressure switch. Tech has changed inducer motor, pressure switch, control board and made sure it was draining properly, also check the slope of the exhaust vent...said it was sloped properly. Still getting this stupid code 31 pressure switch tripped code.

[@grayfurnaceman]

I assume it is Carrier. Some of the older ones had problems if the vent passed thru an unconditioned space. Insulating the vent helped. GFM

[@mxbigd17]

@@grayfurnaceman it is a 2014 Bryant 915sa 80000 BTU furnace, it runs thru my heated basement exiting 21 feet from the furnace, it only has 2 45degree bends and 1 90degree bend. When I remove the 2inch exhaust pvc vent directly at the furnace miraculously the furnace works fine. I have checked and the exhaust pvc is not obstructed with anything and I even put more slope on the pipes for water to drain back to the furnace. Hence, why I was contemplating going to a 3 in exhaust pipe....this furnace is a pain in my ass....

[@grayfurnaceman]

@@mxbigd17 If the venting, including the type of ells used are the correct size, length and type follow the manufacturer's instructions, I guess that is about all you can do. It should not hurt anything, GFM

[@terrydoberstein6742]

I have a question.. I only get the low pressure switch blinking light when I put my cover/filter back on (even with a new filter) Any Ideas? Thank you for Your time.

[@AnswersFromGod_com]

I removed the inducer blower from the furnace, and it inducer blower works just fine, but I am still getting a pressure sensor stuck open code (80%, Guardian furnace). Could the real problem be the pressure switch?

[@arcad1an292]

Please make a video on DOWNWARD venting a 90%+ Furnace.

[@eekay3646]

Sir, let me ask you. I have a 95% furnace and the flue exhaust collar is black. I'm thinking it's ABS. So am I supposed to use red RTV silicone to bond the PVC pipe to the collar?

[@grayfurnaceman]

Yes. Its not about bonding, its about sealing. GFM

[@eekay3646]

@@grayfurnaceman thank you

[@33buddyrich]

For the BTU of my furnace and number of 90 elbows I had to use 3" PVC (manual said 30' run and max of 2 90 elbows for 2" PVC or it might trip pressure switch ) I ended up needing 3x90s and 1x45, though only 10' of actual pipe, but still went 3" to be on the safe side. No issues with pressure switch but it was also recommended to reduce to 2" just beforing going through the wall... Do you know why that is and whywouldn't that affect the pressure switch reducing down?

[@grayfurnaceman]

I have no idea. GFM

[@mikemcelwain]

My fresh air intake doesn’t go to the outside I have 9 foot ceilings in my basement unfinished by 58 feet long is that a problem Oh and also there is a 4 inch radon pipe to goes up through the roof maybe that would help with Fresh air

[@grayfurnaceman]

The space is probably large enough to provide combustion air. If the furnace is designed for outside air, it is best to have it piped outside. The radon pipe does not bring in outside air. It draws out air from the space. GFM

[@Spector_NS5_RD]

You know how many birds I have found stuck head first inside of the venter outlet? Why do they all crawl to the end of the pipe that has no freedom, only 💀? LOL 😆

[@bgavaskar]

How did you get them out ? I have same issue and wondering how to get them out

[@Spector_NS5_RD]

@@bgavaskar I just leave them in there and replace with a new inducer. I'm always worried if i just pull out the bird and stick the same inducer back in, the inducer could fail down the road. When a foreign object, like a bird, keeps the motor from spinning, that motor gets super hot and can damage the stator windings.

[@JAshw84]

Hey Gary, I have a question. Is it safe to put my furnace blower for HEAT to LOW? like the AC? I have a Rheem 16 SEER 2.5 Ton AC and according to the instructions on the condenser, the indoor CFM should at or close to 1000 CFM. This means we had to the Furnace blower to LOW because the charts shows 818 CFM-1208 CFM. LOW MED was 1012-1363 CFM. We can have the HEAT, COOL, and FAN on separate blower speeds OR there is a tap to put the HEAT and COOL on the same speed. I think the AC Company installed a furnace that's way oversize. My AC/Heat square footage is 1047 and they installed a 80% 75K Furnace... In South Florida. Having it on LOW MED to MED is way to much. When I had the HEAT on low, I checked the outgoing temp of the air. The incoming was 70 and out going was 135-145 degrees. According the manual, there should be a 25-55 differential or a maximum outlet temp of 155 degrees. Here is a link resource.gemaire.com/is/content/Watscocom/Gemaire/rheem_r801ta075417msa_article_1403974088948_en_ss.pdf?fmt=pdf to the specification sheet. My model is Rheem R801TA075417MSA. Thank you for your help.

[@grayfurnaceman]

Sorry for the wait. You were in the trash. You can certainly use the low speed if it causes no limit problems. Your furnace is massively oversized. Also, the ductwork is undersized for the furnace. GFM

[@lindseyyah1]

how far should pvc exhaust pipe be from basement window... or any window on a residential property

[@grayfurnaceman]

I believe the code calls for 4'. GFM

[@roberthudanish7405]

most cases 4 feet from the side and 1 foot above with a single pipe system and 12 inches with a 2 pipe system

[@rickbraden4272]

I thought code says for vent pipe that the purple primer is supposed to be used at all connections. I didn't notice any. Also all i saw were cheap 90°elbows in both lines instead of long sweep 90's. Lastly the opening for combustion air intake is supposed to be 12" above anticipated snow level. There's no way in hell that install would ever pass code.

[@electriccar3253]

Look close on the primer. Short radius ells are required for this manufacturer. It is 12" above snow level. Can you say install instructions? GFM

[@rickbraden4272]

@@electriccar3253 For the short radius elbows, my apologies if install calls for them. I've never encountered any manuals other than calling for long radius elbows.Short radius ones increases your equivalent feet in any run. I'd have to see that for myself to believe it. I hope you don't use short radius fittings for line sets too.

[@marvingarcia8982]

Whats up with short radius elbows?? Thats a no no right?

[@grayfurnaceman]

It depends on the manufacturer. Some recommend short radius, some recommend long radius. In this case, Trane wants short radius. GFM

[@grettagrids]

Mine did that too.. had a relative try and fix it and he either blew a fuse or the transformer as now even the digital thermostat won't read ANYTHING.. blank screen and it is wired. furnace does NOTHING now.. not even a BUZZ noise as it was doing off and on but never igniting. so sitting in the COLD as we don't have the Income to pay a repair person. I'd do it myself if I knew what I was doing.. I know how they work but thats it. thanks for Posting and any ideas ?

[@grettagrids]

the thermostat is wired to the furnace so no batteries.

[@grayfurnaceman]

There may be a control board mounted fuse. Other than that, you may have to replace the transformer. GFM

[@enriquebob5.0]

good video thks again

[@grayfurnaceman]

Welcome GFM

[@davidhazen2394]

Hi thanks for the video. I was wondering if you can help me. I have someone wanting to sell me something I don't think I need. Earlier this year I extended my 2 inch id gas heater exhaust pipe out to 35 feet it was 25 feet. I did this to vent the fumes away from where we sit on the deck. I made a mistake when extending it because I did not use enough support straps and it developed a low spot in the pvc pipe which resulted in condensation that got stuck in that low spot and it probably froze or had water built up, causing my furnace to overheat. I fixed the slope , no low spots the water drained out right now and the slope is right. I think I am good, but the Hvac company told me that my 2 inch intake and output should not be placed under deck. In addittion, they told me that I needed to increase 2 inch Id pipe to a 3d ID pipe. . Do you know if they are telling me the truth when they say it should not be under the deck and that I need a 3 inch pipe to go 35 feet. I think since I fixed the slope issue that I might be good with the 2 inch id ran 35 feet?

[@grayfurnaceman]

Generally, venting can be run under a deck. It should be insulated with armaflex. As for the size, the installation instructions will tell you about size. Each furnace is different. Since the furnace did not drop out on a pressure problem, it may be ok. GFM

[@thomaskincaid9157]

I’m in Texas but I still have a venting problem. That or the inducer is bad (it’s motor runs constantly). I changed pressure switch and nothing happened.

[@grayfurnaceman]

There could be a number of problems here. None of which are a failed inducer motor. If you turn off the furnace at the thermostat, does the inducer stop? GFM

[@thomaskincaid9157]

@@grayfurnaceman No, only if I cut power to the entire unit either at switch or breaker.

[@grayfurnaceman]

@@thomaskincaid9157 I would be looking at the relay that starts the inducer. It could be stuck. GFM

[@thomaskincaid9157]

@@grayfurnaceman would that be on the ifc or between the them?

[@grayfurnaceman]

@@thomaskincaid9157 It would be on the IFC. If an IFC controlled furnace has a continuously running inducer, the cir fan should also be running and an error code showing. GFM

[@Sctronic209]

What you didn’t use long sweep Ellis.

[@Guillotines_For_Globalists]

In another video he says the installation instructions for this furnace actually called for the compact radius fittings.

[@filipeoliveira6121]

Thank you !!

[@grayfurnaceman]

Welcome GFM

[@jonathanraul4086]

Thank you nice video or the drain is clogged

[@ryanpetty2537]

thank you sir!!

[@grayfurnaceman]

Welcome GFM

[@orlandojohnson5742]

A 90% furnace deserves a good filter access & better than standard filter!! Install pleated media or good washable type!!! These furnaces have a recuperating coil off of the heat exchangers!!!! Poor filtering can cause the heat coil to clog up(evaporate coil too!). Not fun cleaning those off either!!! If owners properly changed their filters they could have fewer professional visits!? Drain lines & cracked heat exchangers a different story!!! So don’t blame HVAC companies when these problems arise & you haven’t had yearly inspections!!! Jus saying! Nothing’s perfect it’s all man made & maintained!

[@harrydoherty8299]

also i cut the existing pipe just above the furness and the furness ran . so the water block in attic caused problem

[@grayfurnaceman]

Glad you found it. GFM

[@shawnd567]

I'd change out those terrible 90's for some long turn elbows.

[@grayfurnaceman]

Those 90s are recommended by manufacturer's instructions. GFM

[@bymarkhvac64]

Should have used long turn ells on the venting

[@grayfurnaceman]

Not according to the manufacturer's instructions. GFM

[@99f234]

I had a call once for no heat on a high efficient furnace on a pretty cold day. Show up and the inducer is running and coding on ignition failure I believe? I check the venting and the pressure switch tubes. All good. Checked the drainage too and it was fine. I jumpered out the switch after inducer startup and she lights. I say ok, ill go get you a switch. I put it back together before I went to get a new Pswitch, and just out of curiosity I tried to fire it and it relit and after about a dozen resets it kept firing with no issues and I haven't heard from them since. Would this have been a case of possible water in the Pswitch tubing that I didn't see or maybe the Pswitch diaphragm was stuck?

[@throttlebottle5906]

I've hit a few like that, the contacts inside the switch were sticking, maybe due to weak spring or hardened diaphragm. I didn't tear them down to find out, eventually they got bad enough to just stick closed and not fire until banged on, contact would open, unit fired ran until it cycled off contacts stuck and switch error. at first they'd only stick randomly and usually would start working again after being tapped or power cycling the inducer would make it release. I used a data logging meter and caught it acting up first hand. if you checked pipes, tubes, drain for clogs and wrong pitch, then best bet is new pressure switch

[@grayfurnaceman]

It could have been. Sometimes we never know. GFM

[@RockoRocko-rz7kx]

Yes both