I have a Whisper Heat by Lennox furnace, approximately 15 years old, model #G20Q3E-50-2, running on natural gas.

Early in the season I had trouble where pilot would light for a couple seconds and go out, without ever lighting the main burners. Was told to check out the flame sensor, I did and it was rusty and the ceramic portion had cracks in it. I replaced the flame sensor and furnace worked fine for a couple of weeks and now the pilot will light for a few seconds, then the main burners will kick on and stay lit for around 5-8 seconds and go out.

I can sit there and when the main burners go out turn off the power to the furnace, wait a few seconds, and turn the power back on (sometimes it takes several attempts) it will eventually keep running.

I am afraid for the day when it just doesn't run. Luckily so far this has been a pretty mild winter, but I know worse is yet to come. Any help would be greatly appreciated.

John

Is there a second flame detector for the main burner? Also check the connections for the one you replaced. Is it in the right position?

I have checked the connections and they seem clean and secure. I don't see a second flame sensor, unless I am just looking in the wrong area. The way the flame sensor is attached I don't think I could have changed its position.

Any other help would be appreciated.

Thank You

There is only one flame sensor. Is there a diagnostic light on the PC board flashing any codes?

No, I don't see any light anywhere on the unit.