Lennox
Blower Stuck On / Fan Relay Stuck Closed
Furnace blower runs continuously even when 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 thermostat, Stuck blower relay on Lennox control board, Short between G and R thermostat wires, High limit switch open causing fan-only mode
How to Fix / Troubleshooting
Safety: Turn off 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 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 blower continues to run with 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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