Hello and Happy New Year. I get to be the first post in '10.
I have an Ultra 80sx, Model: GUJ125D20-3A, Serial: 8498B12038. The furnace is at least 10 years old.

My problem is – Every so often (maybe once every 12-48hrs) the unit will be on, that is, blower motor, induction/combustion fan, and pilot light will all be on but the burners have NOT lit. So I’m just getting cold air blowing out the vents. This problem started last winter (2008/9) and continues now (2009/10).

I can temporarily fix this by turning off the power to the furnace, waiting 3-5 minutes, and then turning the power on. Then everything works as it should for 12-48hrs, then the cycle repeats.

I have been googling and found numerous posts on both this site and others that are similar, but not exactly the same.

I have tried cleaning the tube from combustion fan motor to the pressure switch. A service man came out last year and replaced a couple of switches/sensors (unfortunately I don’t have the receipt so I don’t know which).

Can anyone recommend some simple tests / fixes that a newbie could handle?

Thanks
Jay

Try cleaning the flame sensor if so equipped. Steel wool or fine sand paper will do the trick