C High

Main C Fault Code

The Main C fault code means: your boiler has temporarily stopped working because it has detected a loose or faulty connection to the internal fan that safely removes combustion gases.. It appears on 2 Main models in our database.

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description: Fan connections check at fan & PCB X11 and X23 connectors
Typical repair cost £90-180 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Main models that show the C fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Main C fault code information on this page is sourced and cross-checked against the official Main service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026