I know this isn't a Geothermal issue, but everyone is so helpful here, I thought I ask anyway. I have a ASHP upstairs and the other day it stopped working, the breakers checked out fine, so I switched the system off at the thermostat and and back on and it started right up. three days later, I noticed it was a little chilly before going to bed, so I turned it temperature up, well the system never turned off, it was 64 degrees in the morning. I switched the system off in the morning. Now I'd wondering what is up with the system, could be as simple as a defective thermostat?

Capacitor is among the most common reasons for failure to start. Typically condenser fan starts but compressor merely hums - hard to tell above condenser fan noise.

Welded contactor is a common reason for failure to stop, though it would require the thermostat be switched to continuous fan ('on') for the failure of the compressor to stop to translate into chilly rooms.

If the blower were set for 'auto' and the contactor failed to open, the combination of the compressor and outdoor fan continuing to run would have resulted in an iced evaporator. In the case of an older fixed orifice system with a reciprocating compressor it can send liquid refrigerant into the compressor, breaking it.

If you observe a failure to stop and the thermostat seems not to be calling for cooling, go out and give the condenser a good slap about as hard as one might a mouthy older child - in other words, hard enough to command attention but not so hard as to break anything. The resulting physical jolt may be enough to 'unweld' the contactor and the unit then stops.

Hope this helps