TP-Link Kasa Fan Control (G Circuit) Misconfiguration or Wiring Fault

Thermostat fan setting does not work as expected (fan will not turn on in ON mode or runs constantly in AUTO mode)

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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 missing G wire, Misconfigured fan control in thermostat, Stuck fan relay on furnace board, Incorrect system type selection

How to Fix / Troubleshooting

Safety: Turn off power to the furnace or air handler before checking the wiring.

  • Check G wiring: At the thermostat and furnace board, ensure the G conductor is connected and secure.
  • Fan mode test: With power restored, set the fan to ON at the thermostat. If the blower does not start, the issue is in the wiring, thermostat G output, or furnace fan relay.
  • System settings: In the Kasa app, verify fan control options and ensure the thermostat is set to control the fan (if your system requires it).
  • Technician test: A technician can jumper R to G at the furnace board. If the blower runs with the jumper but not via the thermostat, replace the thermostat. If it does not run, the furnace fan relay or control board is faulty.
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Repair Difficulty

Hard 4/5

Required Part

Fan Call (G) Circuit / Furnace Fan Relay
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