Viadrus
Fan Stuck On / Control Relay Fault
Furnace fan runs continuously even when there is no call for heat and the burner is off.
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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 fan relay on Viadrus control board, Misconfigured post‑purge time, Shorted wiring causing permanent fan signal, Faulty flue gas thermostat requiring fan cooling
How to Fix / Troubleshooting
Safety: Isolate power before accessing the control board.
- Check settings: In the control menu, verify the fan post‑purge time. A long purge is normal after burner shutdown but should not be continuous.
- Inspect relay: Listen for the fan relay clicking on and off. If the fan runs with the relay apparently off, the relay contacts may be welded and the board needs replacement.
- Wiring check: Ensure the fan is wired only to the designated terminals and not bridged to permanent live.
- Flue thermostat: If a flue thermostat is calling for cooling due to high temperature, investigate flue blockage or burner overfiring.
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Repair Difficulty
Hard
4/5
Required Part
Main Control Board
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