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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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The thermostat is on heat, heat will come, then no heat but

Customer Question

The thermostat is on heat, heat will come, then no heat but the blower keeps on and just air still keeps coming out. I go up to the ceiling and switched for a few minutes then turn it on, I can see the flames coming out and there is heat. later no flames will come out.
JA: Did you double-check the thermostat's settings? And what about the filters?
Customer: I did check the thermostat, it was still on heat and I had replaced the filter.
JA: Do you plan on doing the work yourself?
Customer: If I could, a technician came in and said it might be the board or thermostat.
JA: Anything else we should know to help you best?
Customer: I can see the flames if I turn on and of the furnace but later no flames will come out.
Submitted: 6 months ago.
Category: HVAC
Expert:  Phil replied 6 months ago.

Hello, the problem could be a bad printed circuit board (70% chance) if you want to do a heat stress test on it let me know and I will coach you on heating the board up to 125F with a hair drier.

The problem could also be an intermittently failing flame sensor rod ( 20% chance) solution clean the flame sensor rod.

There is also a pretty good chance that the high temperature safety cut out switch has been tripping (make sure you have a clean air filter in the furnace).

If you rate those answers positively, I will coach you without a time limit on trouble shooting these items depending on your skill levels