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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.
Steve
 

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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.
 

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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!
 

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Discussion Starter · #5 ·
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!
Steve
 

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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.
 

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Thanks!!!!!!!!!!!

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:
 

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Thanks

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.
 

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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?
 

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Clean the face of the burner that the sensor sits in front of with emory paper. It has to conduct the flame signal from the sensor which gets converted to DC current thru flame rectification. If that burner is even slightly corroded or rusty it weakens the signal. Make sure the ground wire from the burners on the right is tight and not corroded if it has one.
 

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Clean the face of the burner that the sensor sits in front of with emory paper. It has to conduct the flame signal from the sensor which gets converted to DC current thru flame rectification. If that burner is even slightly corroded or rusty it weakens the signal. Make sure the ground wire from the burners on the right is tight and not corroded if it has one.

I cleaned it today using the emory paper. It was some what dirty but I cleaned it well. This is a 7 year old unit. I put everything back in order and STILL the same problem :wallbash:

I'm starting to think maybe the circuit board is bad or what??????
 

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There could be many problems. The pressure switch could be dropping out the gas valve could be dropping out and you should check your flame signal with a meter. Has anything been done to the venting inside or out. Is anything in the venting?
 

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There could be many problems. The pressure switch could be dropping out the gas valve could be dropping out and you should check your flame signal with a meter. Has anything been done to the venting inside or out. Is anything in the venting?

There have been no changes to the venting. As far as I know, I don't believe there is anything in the venting...
 

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There have been no changes to the venting. As far as I know, I don't believe there is anything in the venting...


The LEDs are both flashing fast= normal operation, but the burners keep going through the same cycle of only staying on for about 3 seconds... The fans are working fine. Its about 67 degrees inside, and I have the thermostat set to 80.
 
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