I have a concord 80 plus gas furnace. I turn on the temperature control to say 75 and the system starts. Sounds the fan or blower is on, then the glow spark then I can see the gas flames turn on but they only last about 4 or 5 seconds. Then the cycle starts again. Shouldn't the gas flames turn on for minutes and not 5 seconds?

I have a concord 80 plus gas furnance. I turn on the temperature control to say 75 and the system starts. sounds the the fan or blower is on, then the glow spark then i can see the gas flames turn on but they only last about 4 or 5 seconds. Then the cycle starts again. Shouldn't the gas flames turn on for minutes and not 5 seconds?


Clean the flame sensor with sandpaper.