C1
Junkers
Fan speed / air pressure fault
Boiler displays C1; fan starts but ignition does not proceed or boiler shuts down
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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
Defective fan motor, Blocked or restricted flue or air intake, Faulty air pressure switch, Wiring fault between fan/pressure switch and PCB
How to Fix / Troubleshooting
Safety: Isolate electrical power and gas. Do not operate the boiler if you suspect flue blockage.
- External flue check: Inspect the Junkers flue terminal for obstructions and clear them carefully.
- Reset boiler: Restore power and reset the boiler. Listen for the fan starting. If the error returns, proceed.
- Technician checks:
- Remove the combustion chamber cover and inspect the fan wheel for dirt, seized bearings, or foreign objects; clean or replace the fan assembly if needed.
- Test the air pressure switch tubing for splits, blockages, or water; replace tubing or switch if defective.
- Measure fan speed feedback (if applicable) and verify against Junkers specifications.
- Check continuity of wiring between fan, pressure switch, and control board.
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Repair Difficulty
Hard
4/5
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