Troubleshoot heat pump issues

Use these troubleshooting steps if your heat pump isn’t working normally. For example, the heating and cooling modes might seem reversed, or your heat pump might continue cooling even when the Home app says the system is off..

Important:

This article is for troubleshooting heat pumps only.
If you don’t have a heat pump and your conventional system isn’t working normally, go to the Troubleshoot strange heating or cooling behavior article for more help.
If you’re not sure whether 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 appear similar to air conditioners.

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’.
Search for the unit’s model number, then search the web with the brand name and model number to find more information.
Turn off power to your system, then pull off the thermostat display. If there's 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 you have a heat pump, refer to step 2.
If you have a conventional system, refer to the Troubleshoot strange heating or cooling behavior article.

2. Run a diagnostic test on your thermostat

Test both your heating and cooling mode:

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

If your heat pump still doesn't work correctly after a few minutes, continue to step 3 below.

3. Adjust your settings

The instructions depend on which thermostat you have.

Select the thermostat you have:

Nest Learning Thermostat

(4th gen)

Nest Thermostat

Nest Thermostat 3/4ths view

Nest Thermostat E

Nest thermostat e heating

Nest Learning Thermostat

(3rd gen or earlier)

Nest thermostat heating with silver ring

How to tell which thermostat you have

Heating and Cooling are reversed

If your system starts to blow cool air when your Nest thermostat is in heat mode (or if it blows warm air when it's in cool mode), change the settings for orientation of your heat pump.

Nest Learning Thermostat (4th gen) and Nest Thermostat

Open the Home app .
Tap your thermostat.
At the top right, tap Settings .
Select Thermostat.
Scroll until you find Heat pump. It should show which wire configuration is currently selected.
- If the O option is highlighted, select B.
- If the B option is highlighted, select O.
To make sure the issue is resolved, test your heating and cooling again.

You can indicate what system should go with unspecified wires. Empty terminals will show “-”.

Nest Learning Thermostat (3rd gen or earlier) and Thermostat E

On your thermostat, go to Settings .
Select Equipment.
Select Continue Continue.
Select Heat Pump.
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.
To make sure the issue is resolved, test your heating and cooling again.

System will not turn off

If your system continues to run, even if the Home app says the system is off, your reverse valve activation is likely set to seasonal instead of cyclical. Activating seasonally causes less wear on the equipment, but some heat pumps require cyclical activation. To change this setting:

Nest Learning Thermostat (4th gen) and Nest Thermostat

Open the Home app .
Tap your thermostat.
At the top right, tap Settings .
Select Thermostat.
Select Heat pump.
Change the activation to Cyclical.
To make sure that the issue is resolved, test your heating and cooling again.

Nest Learning Thermostat (3rd gen or earlier) and Thermostat E

On your thermostat, go to Settings .
Select Equipment.
Select Continue Continue.
Select Pro setup Continue. You may see other questions based on your system. Continue through the flow until the screen displays a wiring diagram.
Select the Heat pump terminal.
Change the Activate setting to Each cycle.
To make sure that the issue is resolved, test your heating and cooling again.

Note: If the reverse is true and your heat pump is set to cyclical/each cycle when it should be set to seasonal, you might:

Hear a loud whooshing sound at the end of the heating or cooling cycle
Feel a brief burst of cold air at the end of a heating cycle
Feel a brief burst of hot air at the end of a cooling cycle
If you experience any of these issues, use the instructions above to set your heat pump to Seasonal or Seasonally and see if it resolves the issue.

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:

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

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

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