E13
Google Nest
Auxiliary Heat (W2/Aux) Wiring or Configuration Error
Nest thermostat displays E13 and may not control auxiliary heat correctly
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
W2/Aux wire not detected or loose, W2/Aux wired to wrong terminal, Incorrect heat pump balance or aux heat settings, Broken W2 conductor in thermostat cable
How to Fix / Troubleshooting
Safety warning: Turn off power to the heat pump and air handler before working on wiring.
- Inspect W2/Aux at Nest: Remove the display and verify the W2/Aux wire is fully inserted into the correct terminal and not shared with another function.
- Check W2/Aux at air handler: At the indoor unit, locate the W2 or Aux terminal and confirm the same-color wire is attached securely.
- Review Nest settings: On the Nest, go to Settings > Equipment and ensure that auxiliary heat is enabled and correctly identified (electric strip heat vs. gas backup).
- Test aux heat: Temporarily raise the setpoint well above room temperature to force aux heat. Verify that the backup heat source engages without tripping breakers.
If E13 remains, the aux heat relay or control board may be faulty and should be checked by a technician.
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Repair Difficulty
Hard
4/5
Required Part
Nest Thermostat Base (W2/Aux terminal), Air Handler Control Board
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