Dettson
Blower Stuck in Continuous Mode
Dettson furnace blower runs constantly, even when there is no call for heat or fan from the thermostat.
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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 control board, Short between G and R thermostat wires, High limit switch open causing safety fan operation
How to Fix / Troubleshooting
Safety first: Turn off power before accessing wiring or the control board.
- 1. Check thermostat fan setting: Ensure the fan is set to AUTO, not ON. Wait a few minutes to see if the blower stops.
- 2. Inspect thermostat wiring: Remove the thermostat and check that the G wire is not shorted to R or touching other terminals.
- 3. Check control board indicator lights: Some Dettson boards indicate if a limit is open. If the high limit is open, the blower may run for safety; address overheating causes.
- 4. Test blower relay: If the blower runs with the G wire disconnected at the furnace and no call for heat, the blower relay on the control board may be stuck closed, requiring board replacement.
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Repair Difficulty
Medium
3/5
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