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stevea7777 12-17-2008 05:12 PM

Lennox Furnace burner won't stay on
I've got an 88,000 BTU Lennox Elite Series Surelight natural gas furnace (model #G50UH-36B-090-02) that comes on when the thermostat calls for heat but the burner will only stay lit for about 3-4 seconds. It then tries to light again and does the same about 3 or 4 times and then it just quits until I lower the thermostat below the call for heat and then move it back up. Any ideas what would cause this? I'm in Montana and it's below zero right now. Thanks.

yuri 12-17-2008 06:38 PM

1 Attachment(s)
Clean the flame sensor AND the face of the burner it sits in front of with fine emery paper. The flame sensor sits directly in front of the left burner. Looks like a thin nail and is held in place with porcelain. Has a 1/4" screw holding it to the sheet metal. Do this once a year and you will be okay. Try keep the humidity down in the basement and put any fabric softener tissues in a ziploc airtight bag. The fumes from it corrode flame sensors. Saved ya $150.

dinotheminer 12-18-2008 09:22 AM

i have the same problem i tried this if it works i will buy you all the beer ya want. i am in saskaoon and its - 25

danfrain 12-18-2008 08:19 PM

Thanks for posting this picture,Yuri.

I've spent hours looking for one. I've read several places that I might want to take it out and clean it, and had no clue what to look for. I'm going to take someone's advice and wait until the parts houses are open before I try to take it out. I'm thinking they're less likely to break when replacement is less inconvenient than the middle of the night.

Thanks again!

stevea7777 12-27-2008 12:11 PM

Thanks Yuri- Great help. It works now.
Thanks so much for the help. It's been 21 degrees here in Montana and that was a huge help. The sensor didn't even look dirty but cleaning it with steel wool made it work. I really appreciate your help.
Thanks! Have a wonderful year and God bless you!

yuri 12-27-2008 12:16 PM

Glad to Help. Pay it forward and help someone else.


Dream Maker 01-25-2009 08:06 PM

Great fix Yuri, thanks. 14'F here tonight!!!:)

jjc1111 12-24-2009 11:15 PM

Yuri - Great Fix! Thanks!
It's Christmas Eve, and my furnace was exhibiting the problems described in this thread. I cleaned the flame sensor as you instructed, and the furnace works perfectly.

Thank you for sharing your knowledge with homeowners. It would have been difficult to find an HVAC tech during the holiday. Thanks again.

JohnnyTacks 01-28-2010 07:04 PM

Thanks Yuri! It's supposed to be -10 tonight and my furnace was doing this. I cleaned the sensor and voila! My family and I are very thankful!

yuri 01-28-2010 07:25 PM

Good For You!:thumbsup:!

KCRutherford 12-12-2010 09:49 PM

Yuri your post saved the day. It is 9 degrees here in Kansas City tonight and my house was getting cold. I cleaned the flame sensor and the heat is flowing again. Thank you for sharing your wisdom.:thumbup:

Vernster 02-01-2011 12:09 PM

My furnace was acting up on Monday night here in Regina and I managed to get it working. After seeing the LEDs flashing and indicating it was a low signal from the flame sensor, I tried to locate one. Mission impossible. No one will sell gas furnace parts to home-owners and it is impossible to find the parts manual for a Lennox G50UH(X) online. Thanks a lot Yuri, your answer seems to have helped a ton of people.

yuri 02-01-2011 05:08 PM

Glad to help, over 3000 views, must have helped quite a few folks:yes:

echo6romeo 02-07-2011 08:00 PM

Need more suggestions please
I have pretty much the same problem. My Lennox G43 unit will ignite the burners (Nice blue flame) but they stay on only for about 3 seconds and turn off. This ignition process continues for several hours before the unit goes to watch guard mode: failed to ignite...

I have already replaced the flame sensor and the hot surface igniter . I have reset the circuit breaker and changed the air filter.... Any other suggestions?

echo6romeo 02-07-2011 08:02 PM


Originally Posted by yuri (Post 582654)
Glad to help, over 3000 views, must have helped quite a few folks:yes:

I need more suggestions please....

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