Geo
Emergency Heat Command Not Engaging
Thermostat does not enter Emergency Heat mode when selected on a heat pump system.
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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
Aux/E wire not connected to Geo AUX/E terminal, AUX/E output not configured correctly, Failed AUX/E relay on Geo PCB, Furnace/strip heat not wired to thermostat
How to Fix / Troubleshooting
Safety first: Turn off power to the HVAC system at the breaker before adjusting wiring.
- Step 1 – Confirm system supports emergency heat: Ensure your heat pump system has auxiliary electric or gas backup heat wired to the thermostat.
- Step 2 – Check AUX/E wiring: Verify the Aux/E wire is connected to the correct AUX/E terminal on the Geo wall plate and to the appropriate terminal on the air handler or furnace control board.
- Step 3 – Configure AUX/E function: In the thermostat equipment settings, set the AUX/E output to control emergency/aux heat.
- Step 4 – Test emergency heat: With the thermostat in Emergency Heat mode and a high heat setpoint, verify that the backup heat source engages.
- Step 5 – Replace thermostat if output failed: If wiring and configuration are correct but emergency heat never engages, the AUX/E relay may be defective. Replace the thermostat head unit.
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Repair Difficulty
Hard
4/5
Required Part
AUX/E Output Circuit / Main Control PCB
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