We have a two year old Ducane 80G1 gas furnace. We are in the middle of a cold wave with single digit temps. Since the cold wave began, the furnace has been running very inconsistently. Here's what happens: The thermostat kicks the unit on. The impeller pushes air up the flue, then the pilot flame ignites. After a five or ten seconds, I smell gas and the flame goes out. The impeller stays on and the unit goes through the same cycle twice more, then shuts down completely. In the past 24 hours, shutting the unit off, waiting a few minutes, and turning it back on has caused it to run correctly. And it often runs for hours correctly. I replaced the thermostat last night, but the problem is still happening intermittently. I also changed the filter.

I've removed and reinstalled the flame sensor but we are still having the same problem.

The door to the furnace has a list of LED codes, but I can't see an LED anywhere on the unit.

 

http://www.airease.com/_/pdfs/instal...ow_Install.pdf

Can you see it near the thermostat wire connections to your furnace?