Emerson
Continuous Fan Operation
Indoor fan runs continuously even when thermostat is set to Auto
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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
Fan mode set to On in thermostat, Stuck G relay on furnace control board, G wire shorted to R, Defective thermostat fan output
How to Fix / Troubleshooting
Safety first: Turn off power to the furnace/air handler at the breaker before touching wiring.
Steps to troubleshoot:
- 1. Check fan setting: On the Emerson thermostat, ensure the fan mode is set to Auto, not On or Circulate.
- 2. Remove thermostat: Take the thermostat off the wall plate. If the fan stops with the thermostat removed, the thermostat or its wiring is causing the fan call.
- 3. Inspect G wiring: Verify the G wire is not touching R or any other terminal at the sub-base or furnace board.
- 4. Test furnace board (advanced): With the thermostat removed and G wire disconnected at the furnace board, restore power. If the fan still runs, the furnace control board fan relay is likely stuck closed.
- 5. Replace faulty component: Replace the thermostat if it is sending an unwanted fan call; replace the furnace control board if the fan relay is stuck.
When to call a professional: Fan relay or control board replacement should be handled by an HVAC technician.
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Repair Difficulty
Medium
3/5
Required Part
Furnace Control Board Fan Relay / Thermostat G Output
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