Digital thermostat mounted on a concrete wall
Generic photo: Alexander Mass · Pexels License

Indoor fan won't turn off from the thermostat

Start at the thermostat: fan set to ON instead of AUTO, or a setpoint the system can never reach. If the thermostat is right, the cause is in the equipment: a stuck fan relay, a limit switch keeping the blower on, a shorted G wire or a control board fault.

Cross-checked ~40 min moderateBrands: All

Before you start

  • Turn off power to the furnace/air handler before opening panels or touching relays.

Diagnostic steps

Unlock all 4 steps with expected values

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OnCall Tech is a reference tool for trained technicians and can make mistakes. Always disconnect power and confirm with the manufacturer's documentation before you work.

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Indoor fan won't turn off from the thermostat · OnCall Tech