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Nest thermostat won't turn heat off (heat stops on device removal)

parkster618
Community Member

Hi all. I've read a lot of these forums but haven't specifically seen a solution to my issue. AC worked all through summer, but when switching over to heat a few weeks ago I noticed the thermostat does not turn off the heat even when the inside temperature is well above the desired temp.

 

I believe I have an electric system with forced air, though I'm not totally sure. I live in a condo with my unit in my neighbor's space, so if needed I can check, but do not have ready access to it.

 

Here's what I've tried so far after checking for updates (up-to-date) and resetting to factory settings:

  • Turn heat to below current indoor temperature (heat stays on indefinitely)
  • Turn heat off on thermostat (heat stays on indefinitely)
  • Switch OB wire to W (only cold air blows from my vents)
  • Current workaround: Remove thermostat from wall (heat turns off after a few seconds)

 

Plugged in I have a Y, G, and R wire as well as a C and OB wire. Unfortunately I do not have a picture of my old setup, which was successfully turning the heat on and off.

 

What are some steps I can take to troubleshoot this issue? It seems it is rooted in the thermostat or the wiring, as far as I can tell.

 

I am located in the US.

3 REPLIES 3

CoolingWizard
Platinum Product Expert
Platinum Product Expert

@parkster618 , the step to troubleshoot this problem, are many. First of all you need to manually verify the current of the OB and Y wires under operation.  You will need a baseline voltage check between R and C as well.  There is a Defrost Control Board in the outside unit, this DFC can go bad and keep the unit running but that is very rare type of failure.  Can you attain for me the model number of the forced air handler and the outdoor heat pump unit?

The AC Cooling Wizard

NestPro, Google Pro, Mechanical Engineer and HVAC service company owner. If my answer solved your problem, click Recommend this Answer below, and If it helped you, please give a Kudo.

Thanks for your reply, and sorry I didn't get to respond this weekend.

I had a mechanic come out and turns out I may have set up the Nest incorrectly? I think I answered "I don't know" to the question regarding a heat pump -- turns out the app assumed I did when I didn't, and my AC was running constantly at the same time as my heat, so it somehow never knew to shut itself off. I don't know the technical details, but short answer was that setting it up answering "no I don't have a heat pump" solved my issue.

Fortunate timing, as my AC pipes had frozen! Much longer and I think I was running the risk of needing to replace the AC unit.

CoolingWizard
Platinum Product Expert
Platinum Product Expert

@parkster618 , if the ice build up reached the compressor, it can cause a some trouble however not likely as it would have to run for several hours before the POE would have turn to jelly constancy.  The Nest thermostat only assumes there is a heat pump when a wire is placed in OB or *OB terminal.  When that happens it generally asks the question is this a heat pump. The * is a programable terminal and can represent many things.  I am glad to hear your thermostat is set up properly now. 

AC Cooling Wizard

NestPro, Google Pro, Mechanical Engineer and HVAC service company owner. If my answer solved your problem, click Recommend this Answer below, and If it helped you, please give a Kudo.