Lennox
Blower Stuck On / Fan Relay Stuck Closed
The furnace blower runs continuously even when the thermostat is not calling for heat or fan.
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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 set to ON at the thermostat, stuck blower relay on the Lennox control board, a short between G and R thermostat wires, or a high limit switch open causing fan-only mode.
How to Fix / Troubleshooting
Safety: Turn off the power before removing furnace panels.
- 1. Thermostat setting: Ensure the fan mode is set to AUTO, not ON.
- 2. Check for high limit trip: If the furnace recently overheated, the blower may run to cool the heat exchanger. Replace the dirty filter and clear airflow restrictions.
- 3. Inspect thermostat wiring: Look for a short between G and R at the thermostat and furnace board.
If the blower continues to run with the G wire disconnected, the control board fan relay is likely stuck and needs replacement.
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Repair Difficulty
Medium
3/5
Required Part
Lennox Integrated Furnace Control Board
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