How to Fix / Troubleshooting

Safety: Turn off power. Do not bypass safety controls to force the fan.

Steps:

Check for obstructions: Remove the fan access cover and inspect the combustion fan wheel and housing for foreign objects or heavy dust buildup. Clean carefully with a soft brush and vacuum.
Manual rotation: Try to rotate the fan wheel by hand. If it is stuck or very stiff, the motor is likely seized and must be replaced.
Inspect capacitor (if present): Some Buderus models use a start/run capacitor mounted near the fan. Look for bulging, leaking, or burned terminals. A failed capacitor can prevent the fan from starting.
Check wiring harness: Ensure the fan motor plug is fully seated on the control board and that no pins are bent.

If the fan still does not start and C6 persists, a Buderus technician should test the motor and control outputs and replace the faulty component.

Error C6, furnace will not fire, fan may not start

Possible Causes