reznor nat. gas garage heater unusual operation
 

I have a model 45t heater that is about 7 years old. I always keep it on minimum thermostat setting so the garage stays about 40f. It stopped working. I checked out the wall thermostat and power to the circuit board and all seems fine. I can get it to work normal by blowing a heat gun into the operation syster (circuit board, trans former, etc.) and it will continue to work fine as long as I have the heat setting at about 55f., below that it will not go on automatically. To get it to run again I repeat heating up the operating system for about 30 seconds and it will go on and run a full cycle
(fan, heat, etc.) but unless I turn the thermostat up to about 55f. it will not run again without me repeating the heating up process.

Hmm. and you think the thermostat is working Ok. Sure sounds like the thermo to me. Have you checked the Furnace Filter to see if it's clogged? Seems like I've heard that can cause this sometimes, could be wrong.