I have a janitrol furnace serial # 6491074 size UA585-14. We have to push in and hold the (ignitor?Pilot?) button for several minutes before it will stay lit. Then it seems after it runs for a bit, the pilot light is still lit, and the fan is still running, but it won't blow warm air anymore. What could be the problem? Someone suggested the thermocouple, but someone else just said that can't be the problem since the pilot light is still lit. A gas valve, maybe?

Need to know exatly if this unit has a thermocouple, or a powerpile. If thermocouple, then the couple is not the problem, as your friend said, if you have a bad thermocouple, the pilot will not stay lit. However, if it is a powerpile, it may be producing just enough energy to keep the pilot lit, but not enough to kick the gas valve on, or keep it on.