Furnace shows C4, blower or fan does not operate correctly
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.
Possible Causes
How to Fix / Troubleshooting
Safety: Disconnect power before removing blower or fan covers.
Steps:
- Listen and observe: When calling for heat, listen for the fan attempting to start. A humming sound without rotation suggests a seized or failed motor.
- Inspect fan wheel: Remove the fan access panel. Check for debris, insulation, or wiring interfering with the fan wheel. Clear any obstructions.
- Check wiring: Verify the multi-pin connector from the Buderus control board to the fan motor is fully seated and not burned or corroded.
- Spin test: With power off, gently spin the fan wheel by hand. It should rotate freely without grinding. If stiff or noisy, the motor bearings may be failing.
ECM or variable-speed Buderus fan motors and their feedback circuits are complex; if C4 remains after basic checks, the fan assembly or control board likely needs replacement by a professional.
Repair Difficulty
Required Part
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