Troubleshoot heat pump issues

Use these troubleshooting steps if your heat pump heats when your Google Nest thermostat is in Cool mode, or your heat pump cools when when your thermostat is in Heat mode


  • This article is for troubleshooting heat pumps only.
  • If you don’t have a heat pump, and your conventional system is not working normally, go to the Troubleshoot strange heating or cooling behavior article for more help. 
  • If you’re not sure you have a heat pump, start with step 1.

1. Make sure you have a heat pump system

Generally, conventional systems (like a furnace) are located inside the home and only produce heat. Heat pumps are typically located outside of the home and look like an air conditioner. 

Check the following to tell if you have a heat pump.

  • Check the manufacturer or EnergyGuide labels on the unit for the words “heat pump.”
  • Look for the unit’s model number, then search the web with the brand name and model number to find more info on the unit.
  • Turn off power to your system, then pull off the thermostat display. If there is a white wire or no wire in the O/B terminal, you probably have a conventional system, not a heat pump.
  • Set your Nest thermostat to Heat mode. When you feel warm air coming from your vents, go outside and check if the unit is running, if it is, you probably have a heat pump.

If you have a heat pump, go to step 2.
If you have a conventional system, go to the Troubleshoot strange heating or cooling behavior article.

2. Run a diagnostic test on your thermostat

Test both your heating and cooling.

  1. Set your thermostat’s mode to Heat.
  2. Raise the target temperature until the thermostat display turns orange.
  3. Wait a few minutes and check the air coming from your vents.
  4. Repeat steps 1 to 3 for Cool mode.

If your heat pump is still not working correctly after a few minutes, continue to step 3 below.

3. Change the O/B wire settings

If your system starts to blow cool air when your Nest thermostat is in Heat mode (or if it blows warm air when its in Cool mode), change the settings for orientation of your heat pump.
The instructions depend on which thermostat you have. 
Select the thermostat you have:

Nest Thermostat

Nest Thermostat 3/4ths view

Nest Thermostat E

Nest thermostat e heating

Nest Learning Thermostat

Nest thermostat heating with silver ring

How to tell which thermostat you have

Nest Thermostat 

  1. Reset your thermostat. Go to Settings Nest settings icon and then Factory Reset
  2. Begin thermostat setup with the Google Home app again. On the main screen, tap and then Set up a Nest product.
  3. Re-enter all the wires connected to your thermostat. Double check that you account for any unconfigured wires.

Nest Learning Thermostat and Thermostat E

  1.  On your thermostat, go to Settings Nest settings icon.
  2. Select Equipment.
  3. Select Continue and then Continue.
  4. Select Heat Pump.
  5. The Nest Thermostat defaults to an O setting for heat
    • If the O option is highlighted, select B.
    • If the B option is highlighted, select O.
  6. Test your heating and cooling again to make sure the issue is resolved.

4. Check the wire

Before you begin, turn off the power to your system.

Note: If you have a conventional heating system, there shouldn’t be a wire in the O/B connector.

If changing your O/B wire settings didn’t resolve the issue, change the wire’s connector in the Nest thermostat. 

  1. Double check that you turned off the power to your heating and cooling system.
  2. Remove the wire in the O/B connector.
  3. Make sure that the wire doesn’t have any corrosion, that it’s straight, and that there is between ⅓ and ½ inch of exposed copper. If not, clip and re-strip the wire.
  4. Put the wire back into the O/B connector. Make sure the wire is fully inserted and that the O/B connector button stays down.
  5. Put the thermostat display back on. 
  6. Turn your system’s power back on and test heating and cooling again. See step 2 for next steps.

If you weren’t able to resolve the issue with the troubleshooting steps above, contact a local pro to check your system.

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