Miller
Stuck Blower Relay or Open Limit
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
Stuck blower relay on control board, Open high limit switch, Miswired thermostat fan circuit, Short between R and G
How to Fix / Troubleshooting
Safety: Turn off power before removing furnace doors or touching wiring.
- Check thermostat fan setting: Ensure the fan is set to AUTO, not ON.
- Remove G wire: At the control board, disconnect the G (fan) wire. If the blower stops, the thermostat or wiring is calling for fan and should be corrected.
- Test high limit: If the blower continues to run, test the high limit switch for continuity. An open limit can cause the blower to run continuously for safety. Replace a failed limit and correct any overheating issues.
- Replace control board: If the limit is closed and G is disconnected but the blower still runs, the blower relay on the Miller control board is likely stuck and the board should be replaced.
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Repair Difficulty
Medium
3/5
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