Lennox Furnace will not Ignite

I turned on the thermostat, and the furnace main blower never came on. I went to have a look and the blower that is called the combustion air blower was working, but the flue was not warming meaning something was wrong in the ignition system: Igniter, flame sensor, gas valve, etc. After a little review of the service manual, I suspected a pressure switch issue was preventing the gas valve from opening. There is a rubber hose that connects to the outlet plenum of the combustion blower to a pressure switch. The switch closes when exposed to a small amount of pressure. The control board makes sure the switch is open when the combustion blower is not on. Then, it confirms that the switch closes when the blower is on and gas is allowed to flow. Note that the furnace has two LEDs that also indicate what is going on, and if any faults are detected. To diagnose what what going on, I removed the rubber hose and tried to blow into the combustion blower plenum. It was clogged. I found a stiff piece of wire, inserted it into the port and felt the obstruction break away. I reconnected the rubber hose and the furnace now works.
FYI: completeheating.ca/images/pdf/Lennox80MGF.pdf

[@DuaneBurgess-v8j]

We haven't had heat for 5 days. I replaced the ignitor, but that didn't do it. I found this video and you nailed it! Hole was plugged with corrosion. Cleaned it out and it's now working perfectly!! Happy wife, happy life! Thank you!

[@spear101520]

7 years and counting you’re still helping people through this video! Thanks man!

[@dzllamas]

Looked all over the internet. My symptoms were fan would come on, shut off and never send signal for heat. Normal operation then switched to slow blinking green light saying a blockage somewhere. Took off little hose and cleaned with a eyeglass screw driver, broke rust free fired right up! Thank you from KS where its supposed to drop to 30 tonight.

[@joniepstein7125]

DUDE. Thank you! Short story: husband is traveling, house is freezing, 3 year old is going to bed, heat is not blowing. Boy goes to sleep, mommy checks indicator lights, Googles the net and finds your youtube vid. WONDER WOMANNNN! Thank you, sir, for sharing and for writing the description so it was tagged in such a way that it was easily found.

[@peterhou4998]

Thank you so much, it's fixed the problem. I took the pipe out I didn't see any clog inside, but I clean it anyway, and I also clean the connectors just like you did in the video, and the fire is now firing up and work.

[@adaminpeds]

Thank you sir! You saved me a 250 dollar service call. That was the exact problem. It wasn't sanding the flame sensor this time that led to a 150 dollar service call 4 months ago. You're a wonderful person for taking the time to help out and for this video. Thank you again!

[@keoghm118]

Thank you for this video! You saved me from paying hundreds of dollars for a service repairman to fix something so easy!

[@ihealthventures]

Thanks a million for this video. My furnace stopped working suddenly and it was freezing in the house with snow outside. Not sure what to do and who to call. I watched your video carefully - I blew thru the tubes and cleaned with the paperclip and wow!!! - the fan turned on and it started working. You are the real Santa for me this Christmas!!!! - saved me a boat load of money.

[@johngregory3342]

dude, you just saved me $500! Probably more since I'm sure the HVAC guys would have told me I needed a new furnace. All it took was 5 minutes and a paperclip. Genius!

[@petery9602]

This was exactly my problem and such an easy fix. Thank you so much for posting this. You are saving us all a bunch of money and time.

[@goosenglinker]

This was exactly my issue. The red tube wasn’t clogged on mine, but I put a paper clip into the little hole on the part that it connects to. I could tell right away that it had crud in there. Thank you very much!

[@sseunath1]

Hey man, I was frantically looking for an HVAC contractor, then it struck me... check KZbin. I saw your video and did exactly what you said. Two minutes later, I was getting heat. Thank you man, you saved me a lot $$$

[@balogunvictor9076]

God You for this short video,it really goes a long way for me and my family

[@haoelnas1701]

God Bless you kind sir. You have saved me from untold amounts of wasted money, time and discomfort. Thank you so much for sharing this wisdom.

[@voiceofreason2743]

Still saving lives 7 years later! Worked like a charm. Thanks bro.

[@masembach]

Thank you! Like so many others who have commented, you saved me a service call fee. Much appreciated

[@jlo5470]

You just saved me some serious dough!!! My heater wasn’t turning on after I switched new batteries on the thermostat. Tried this on the furnace (Newer model Lennox)and it worked instantly! Thank you I really appreciate it!

[@msani6368]

very cool, you pointed me to the right place, for me it was the pressure sensor relay that was bad. Thank you!!

[@rior1790]

Awesome. because of your video I'm no longer in the cold! a bird prevented the pressure. after removing the deceased birdie from the flue/exhaust... the furnace began to fire up instantly. you saved me many dollars. gas valves, ignition module, control board etc. THANK YOU my fellow American

[@RobDLion]

You just saved me a shit ton of money on the very first day of 2024. This was EXACTLY the problem. All fixed here in cold Colorado.

[@daashee7290]

Great troubleshooting step. My problem was exactly what was explained here. Mine is an Amana model and I unplugged the small hose to the unit and cleaned it up a little and heat was back on. Thank you! You saved me a lot.

[@RLWatPDX]

Thanks, this simple fix (the outlet plenum of the combustion blower) finally resolved the igniting problem on my G24M heating unit. The Lennox SureLight Ignition System keeps trying 5 times to start and pretty often would end with the failure indicator, both LEDs alternating flashing. Error code for the bad behaving combustion air blower pressure switch, was hidden in the full sequence of SureLight trying 5 times. My system would fail reproducible after the first try. After 45 seconds burners on, the main ventilation in door blower motor would kick in, and this would always trip the "air blower pressure switch". A few more retries and often the system would work, but once a day it would go into the failure mode for 1 hour with "LEDs alternating flashing". "Watch Guard Mode - Burners Failed to Ignite". Tried many other things first, that did not help. Cleaned the flame sensor, did not help. Lose contact on flame sensor, did not help. Started worrying about the Temperature Limit Switches, did not help. Bad controller board, maybe. All is working now, every heat request, unit starts without re-tries.

[@keithshoemaker6034]

I love how you talk like you know what you talking about using big fancy words but you sound like a total infidel

[@sulivel]

Keith Shoemaker 😁 well I’ve tried a few things now it’s back to not working 😭.

[@joshfeather402]

I had to use a small nail, but worked like a charm. My hose was black and fed off the right side of the furnace. Forgot to pull the model # and too cold to go back downstairs again but it's Lennox. Thanks man, saved me some $$!!

[@Pedalpusher2]

Followed your clear, simple instructions and presto, furnace kicked on with all cylinders firing! I appreciate your generosity to share your video tip!

[@joebinglei9679]

Two thumbs up and thank you very much for the video. I cleaned the flame sensors earlier, even though they were not that dirty. That did not help, but I took that hose off and cleared the pressure switch end with a paper clip and now it is blowing hot air again. So glad I do not have to buy any parts, as everything seams to be going up in price. Also, I'm a customer of NW natural in Oregon. And they do free service calls for their customers and check for leaks and will troubleshoot something like A Furance if it is not working correctly.

[@howardtaylor229]

My exact problem! Everything has been going wrong around my house all at once and now this. You probably saved me $150-200. Thank you.

[@trevorvance2298]

Man I thought it was a bad pressure switch was about to order a new one which would have taken a couple of days. There was a blockage and I took a paper clip to unclog it. Instantly fired up, Thank you

[@johnsnyder6646]

Great video. All others focused on the line down to the pressure switch. My furnace would spool up but not ignite. Saw your video, and realized I never checked the fixture at the furnace side. Sure enough, CLOGGED, no air would pass. Thanks for saving me $$$$$ on a Saturday morning!!

[@lfdenucci]

This was my problem also! It's fixed and cost nothing. THANK YOU!

[@thaddeussherer859]

One more testimony of success! Thank you for taking the time to upload and post!

[@kylegurley5331]

Thanks for the video! Worked as described. Woke up to a 66 degree house and was dreading calling a service person to come take my money. Explanation was clear and sounded reasonable, so I decided to give it a shot. I had a container of paperclips next to the computer, so I was already equipped for the task! Lol Got the hose off and slowly pushed the paperclip into the metal tube behind the fan, felt the resistance and gave little push and repeated that until it went in smoothly. Put the hose back, fired it up and immediately saw the igniter light up and seconds later those wonderful little blue flames were doing their happy dance! I'm guessing I saved at least $75 on the repair call just for someone to come out and look at it, then whatever they would have charged for "parts replacement". I have a Lennox ML180UH gas furnace.

[@LightninLandry]

Thank you so much! This bailed me out during the awful outages in Texas. In the few small times we’ve had power, we could get heat because of this video. I wish I could buy you a beer!

[@bt29hazzard]

Just did this in 2 degree weather after waking up to no heat...cheers!

[@dwiggins1]

Thank You very much!! I have the exact same furnace, did exactly what you did and Bingo!!! it worked I now have heat!! Thank you again for you video.

[@lenzoj]

its 4am and im down here fixing the furnace and i got it to work thanks to your video, much appreciated

[@desertadventuresftw529]

Wow man, thank you!! I did take it a step further and actually removed the little round (black) sensor and tapped it around a bit to help dislodge anything that may have been stuck. Works like a champ now.

[@jessedouglas7589]

My exact problem. Thank you so much for posting this. I have a G50UH, and it was this problem.

[@bradleychampagne9703]

Dude thank you for posting this I changed my ignitor and pressure switch and it still did not work. After watching your video I put a wire down the exhauster orifice and she fired up. Thanks Again

[@BarryConnerty]

Can't thank you enough my man. Worked perfect and just saved me a repair bill and a cold night. Cheers!!

[@williesmith]

Thanks for this Video!! This solved why my heat wasn't turning on!!

[@jonathanmancino2123]

Awesome! Helped me a bunch! Igniter was not working but had continuity, and no codes on furnace, so I was stuck. This got me up and running!

[@jeovannyhernandez6042]

Thank you so much I had the same problem I cleaned the hole that was clogged and now it works

[@acerjuglans383]

Interesting. I have a low-tech Mr.Heater furnace in my garage. When it doesn't come on, this is the exact same type of "repair" that I have to do too.

[@rb8419]

I never post but this was exactly my problem. Thank you! I can repeat a lot of other comments. You saved me a repair bill and cold night.

[@wesreichert7660]

First video i looked at, and it solved my issue as well. Thanks, Boss.

[@blazingocean]

This is a wonderful post!! I have followed your video and fixed my furnace issue. Thank you!

[@samlonzo70]

I did it your way and it worked. Love you man .

[@jillbrecheisen5991]

Thank you, thank you! So glad you did this video. Worked perfectly.

[@MrWongYukMan]

hihi, first of all. THANKS!!! my lennox furnace model is different from yours. and, your discription ' ...Igniter, flame sensor, gas valve, etc.... ' honestly scared me off. plus, blowing into the tubes sounds crazy to someone who seldom touch a fuse box. but, thanks and thanks. its working now. will check it again tonight. hope things go fine. keep in touch

[@enzo2588]

HVAC repair just stopped in and did exactly what you showed in the video. I know what to try next time to save a bit of money.

[@pradeepsali8931]

Thank you Sir, This is really helped me and worked for me, Thank you 🙏🏻 please post more videos 🙏🏻

[@michaelkuc2648]

thank you for sharing your knowledge, I followed your instructions, and my furnace fired up. Again thank you so much.

[@johnchen8888]

Thank YOU! Your video saved the day: we have the same issue and it's resolved today using your method.

[@wdrum63]

Thank you for the video. I couldn't figure out why my furnace wouldn't heat. This was the first thing I tried. It worked great.

[@gordonsmith3722]

Lennox innovator series dimension won’t run

[@leeangelle1373]

Omg, thank you so much. So simple when you know, totally lost if you don’t. Thank you. Thank you. Thank you.

[@samj4822]

Thank you for the video. Exactly the same problem and fix for me. I have a different Lennox model (G40UH-36A-070-10).

[@mattgallegos7296]

Thanks! Same exact thing wrong with mine. Fixed the problem!

[@peterhou4998]

This fixed my furnace problem, thank you very much.

[@cochell]

huge! Saved me too!! This is outstanding!!

[@Jerry_Gormley]

Fixed my furnace.. Thanks!

[@bnelski0257]

I just did this and it worked!! Thank u

[@morriszlotnik1096]

I used a can of compressed air first but that did not work. I then used a wire and that did the trick. Then I cancelled the service call. Thanks for the video tip!

[@alyinug3705]

Thank you so much for the video... save my bother-in-law so 💰.

[@marshallwhitley82]

This is the first video I watched and the first thing I tried. Either way it worked and you saved me a bunch of trouble.

[@apadanastore5819]

I tried this and fixed the heater! Thank you so much for this video! :)

[@williecoleman6775]

It actually works thanks for sharing

[@marionwinger7031]

Exactly as you said, furnace works great now! Thanks!!

[@NightSpyderTech]

Quick and to the point. Thanks for the tip.

[@JayKunkel]

Thank you! Worked for me. Saved me time and money.

[@joshuapabst1694]

Wow man amazing! This just worked for my furnace! Unbelievable!

[@messiah653]

Thank you! This was the problem! Try this first. Now it is working great!

[@nicholasp.devries9020]

Great fix! Thank you for posting!

[@mishaellennon7793]

Thx a lot ,i just did that to mines and it start working correctly again 🙏🏽🙏🏽🙏🏽

[@khkartc]

Seems to have worked. Thanks!

[@zykkfyw]

Had the same issue on a Lennox G40UH .. this fixed my issue ....thanks

[@teesalmon]

Just wanted to add a comment: my furnace would not lite again. That port was really clogged, I had to use a 1/16 drill and it is tight to get a drill in there due to the external fan on the motor, but that solved the problem. I should see what is corroding. The other furnace has never done this....

[@donbuckner123]

Yes, this worked. Thanks so much. Huge save!

[@mikeinco]

Thank you. It was the same problem on our furnace.

[@casa_estrada]

It worked! Oh my!! Thank you very much!!!

[@matthewryan6740]

Thank you so much, that was our problem!

[@rickl7024]

Great 👍 quick video and right to the point! I like!,,,, just bought a new Lennox furnace last year,, still working great so far,, I do know it does use a pressure switch like yours does

[@williamgates5679]

thanks, saved me a bunch of money.. great video

[@MrDardania79]

You just saved me 100bpossibly more thanks a lot

[@mrmarketcap]

perfect - thx for posting I'm the dummy who replaced the pressure switch before seeing this.

[@kb5nhj]

Thanks, this fixed my furnace.

[@Kieuthibui4]

You are awesome man. It worked. Thank you very much❤️.

[@x96kio]

I had the same issue. I blew through tubes from the pressure switch when unhooked and they were fine. So I stick a wire in the ports on the switch and one was a bit clogged. Water then poured out. Fixed it.

[@iDenverRepairs]

We had water pour out too. Wonder what caused the water to be in the pressure switch?

[@lucasatkinson92]

THANK YOU!!!

[@jimbopiskapo8420]

Thank you bro u just saved me some money 🤑👍👍

[@I_M_VNGNC]

Thanks! Solved my no heat issue!

[@stecher02]

OMG! Thank you.

[@vsltransporters4376]

Awesome 👏🏽

[@terencemedina9277]

Thanks bro 🙏

[@genesisreloaded1728]

Fantastic information, it did solved the issue with my furnace. THANK YOU for sharing!!!!!

[@phyllislee8670]

Thank you so much!! Totally worked for me.

[@akniyetimambekov8327]

thanks! same issue, quick fix.

[@bcooley2]

Very helpful, thank you!

[@bobwarner1588]

GREAT TIP...TY!

[@charliehess4052]

The light inside the where 1 st would blink off and on 2 nd ?would stay on ?

[@marcozhao2224]

ty so much. although I can't lose the hose but it started working right away when I shake it

[@danielhankemeier4860]

This does not look like my furnace, Lennox Model CCS16-411-100-5P????