C6 High

Worcester Bosch C6 Fault Code

The Worcester Bosch C6 fault code means: your boiler has detected that the internal exhaust fan is spinning faster than it should, so it has shut down as a safety precaution to prevent incorrect combustion.. It appears on 42 Worcester Bosch 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 speed too high.

What causes the Worcester Bosch C6 fault?

This fault occurs when the boiler's internal computer detects that the fan is spinning at a higher speed than required for safe combustion. Often, this is caused by a communication error between the main control board and the fan, or a physical blockage in the flue that disrupts the internal air pressure. Over time, electrical components within the fan motor can also wear out, leading to unpredictable speeds that trigger an automatic shutdown.

This fault can be more frequent during periods of high wind, as strong gusts entering the flue can interfere with the fan's pressure readings and rotation speed.

Typical repair cost £180-350 (including labour)

Engineer required

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

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Worcester Bosch models that show the C6 fault code

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

Source

Worcester Bosch C6 fault code information on this page is sourced and cross-checked against the official Worcester Bosch service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026