Heil NG furnace, forced draft, intermittent ignition, about 10yrs old. It fires fine after a call for heat from t'stat, with all areas of the burner lit. However, after about 10 minutes the burner looks as if only about 25% is lit. I'm not sure if it ever completely dies out. I don't think so because there must be enough of a flame to allow the blower to continue to blow fairly cold air into the house. Is the gas valve slowly closing or is there a sensor going.

All replies are appreciated, even more so by my wife :eek:

Adam

Could be the valve or the pressure regulator in the valve that is causing this problem.