Alpha
Blower Stuck in Fan-On / Limit Mode
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
Thermostat fan set to ON instead of AUTO, Stuck blower relay on Alpha control board, Open high limit switch causing safety fan operation, Shorted G (fan) wire to R (power)
How to Fix / Troubleshooting
Safety: Turn off power before inspecting wiring.
- Check thermostat: Ensure the fan setting is on AUTO, not ON.
- Inspect thermostat wiring: Remove the thermostat and verify that the G wire is not shorted to R or other terminals.
- Observe control board: With power on and no call for heat or fan, check if the board indicates a limit fault. If so, the blower may be running to cool the furnace due to an open limit.
If the blower continues to run with correct thermostat settings and no limit fault, the blower relay on the Alpha control board may be stuck and require board replacement.
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Repair Difficulty
Medium
3/5
Required Part
Alpha Integrated Furnace Control Board
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