F8
Saunier Duval
Fan Speed / Fan Feedback Fault
Boiler displays F8 and locks out, often with no fan operation
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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
Faulty fan speed sensor (Hall sensor) on fan, Fan motor failure, Wiring fault between fan and PCB, Defective PCB fan driver circuit
How to Fix / Troubleshooting
Safety first: Isolate power and gas. Do not run the boiler with the case removed.
Steps to check:
- Access the fan assembly at the top of the boiler.
- Check that the fan impeller is free of debris and spins smoothly.
- Inspect the multi-pin connector from the fan to the main PCB for secure fit and no corrosion.
- Look for signs of overheating or burning on the fan body or PCB around the fan driver.
- Reset the boiler. If the fan does not start or F8 reappears, the fan assembly usually needs replacement; in some cases the PCB is at fault.
Warning: Fan and PCB replacement should be carried out by a qualified heating engineer due to combustion safety implications.
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Repair Difficulty
Hard
4/5
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