I have a York Electric Furnace (10 years old) with a outside heat pump. Something weird happened recently as we started to use the furnace more often as it gets cold now.
I usually turn on the heat when I wake up and turn it off before I go to sleep. However almost 95% of the time when I tried to turn off the heat, the heat pump and the heat would stop right away, but the furnace fan would just keep on running for the entire night, unless I turn off the circuit breaker. The weird part is that sometimes I get lucky and it actually turns off the fan as it should.
I don't remember this problem in the summer when I use the AC in the summer, back when the furnace would behave and turn off the fan as instructed.
I have so far replaced the thermostat with the Alexa smart thermo, and the issue persists. I have also tried unplugging the thermostat while the furnace is running, and it doesn't really affect anything and the fan kept on running. So I am assuming the issue isn't at the thermostat.
I also doubt if it was the fan limit switch, as there is nothing wrong with the heat. the heat would turn on / off normally.
I have thought about the possibility of a stuck relay. However whenever I turn off the circuit breaker and turn it back on, the fan would actually be stopped. It would run when I turn on heat again, until after heating for a while it would fail to stop again. Does this sound like a stuck relay?
Any thoughts are appreciated, thank you guys.