As the title suggests, my furnace will sometimes shut off as if it's reached the target temperature, while it is still far below (ex. set to 70F, stops at 63). If I unplug the thermostat, the furnace will turn back on (even before I plug it back in).
This happens when running on a schedule or on 'permanent hold'. It doesn't happen reliably, sometimes it goes until the target temperature is reached and turns off normally. It may be related to temperature (it might take more resets to go from 60 to 65 than from 65 to 70), though I also just might not notice as much at higher temperatures.
It seems to me that either:
- Something is wrong with the thermostat, and unplugging it (switching from wall to battery power) updates the signal appropriately.
- Something is wrong with the furnace, and I'm overriding some shutoff condition.
The second one sounds dangerous, though I hope that the furnace is smart enough to not be overridden if it's unsafe.
What's going on here?
UPDATE:
The thermostat is a Honeywell model TH6210U2001:
The pins connect to the base plate which connects WYGR wires to the furnace and air conditioner (separate units).
The furnace is a Jonson AirEase 80 Plus.
Best Answer
A professional HVAC guy would have a spare tstat and swap it for testing if you were bent on keeping the old thermostat. Unfortunately, while for a century furnace thermostats were as reliable as a rock, and nobody would ever suspect them, furnace thermostat makers have discovered if you build it just expensive enough to last 5 years, when it breaks people will just accept it because so much other electronics these days has designed-in short lifespans. Then they will buy another.