E13
Nest
Second‑Stage or Auxiliary Heat Call Fault (W2/Aux)
Nest thermostat displays E13 and reports a problem with the W2/Aux wire or second‑stage heat/aux heat
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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
Loose or disconnected W2/Aux wire at Nest base, Loose W2/Aux wire at furnace or air handler, Misconfigured heat stages in Nest settings, Shorted W2/Aux conductor in thermostat cable
How to Fix / Troubleshooting
Safety: Turn off power to the HVAC system before working on wiring.
- Check W2/Aux at Nest: Remove the Nest display and verify the W2/Aux wire is fully inserted and clamped.
- Inspect furnace/air handler: Confirm the same conductor is attached to the W2 or Aux terminal on the control board.
- Settings verification: In the Nest settings, confirm the system type (multi‑stage furnace or heat pump with aux heat) and that W2/Aux is enabled appropriately.
- Cable check: Inspect the thermostat cable for damage or shorts involving the W2/Aux conductor.
- Professional diagnosis: If wiring and settings are correct but E13 persists, the control board’s second‑stage relay or the Nest output driver may be faulty and should be checked by a technician.
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Repair Difficulty
Medium
3/5
Required Part
W2/Aux Heat Call Wire
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