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 systems.

  1. Press the thermostat ring and select Mode. Change it 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 the process for Cool mode.

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

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.
  1. Press the ring to access the Menu.
  2. Turn the ring and choose Settings.
  3. Select Equipment.
  4. Press Continue and then Continue.
  5. Select Heat Pump.
  6. The Nest Thermostat defaults to an O setting for heat pumps.
    • If the O option is highlighted, select B.
    • If the B option is highlighted, select O.
  7. 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.

Note: Nest Pros are a network of independent companies or contractors not employed by Google.

Was this helpful?
How can we improve it?