Saunier Duval
Fan Overrun / Control Fault
Furnace fan runs continuously even when there is no heat demand
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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 PCB,Overheat condition requiring extended fan run,Faulty temperature sensor reporting high temperature,Incorrect wiring of external controls
How to Fix / Troubleshooting
Safety first: Turn off power before accessing internal components.
- Allow cool-down: After a high-load period, some overrun is normal. Wait to see if the fan stops after several minutes.
- Check sensors: A technician should verify readings from flow, return, and flue temperature sensors.
- Inspect PCB: Look for signs of a stuck relay or burnt components on the control board. Replacement may be required.
- External controls: Ensure no external signal is falsely calling for fan operation.
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Repair Difficulty
Hard
4/5
Required Part
Main Control PCB
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