How much does it cost to fix Worcester Bosch error code C1?

Typical repair cost for the Worcester Bosch C1 fault is £150-300 including labour.

C1 High

Worcester Bosch C1 Fault Code

Q: What does the Worcester Bosch C1 fault code mean?

Your boiler has detected that the flow of air required to safely vent fumes is not moving correctly, and it has shut itself down to prevent unsafe operation.

The Worcester Bosch C1 fault code means: your boiler has detected that the flow of air required to safely vent fumes is not moving correctly, and it has shut itself down to prevent unsafe operation.. It appears on 25 Worcester Bosch models in our database.

Technical description: Differential pressure switch has opened during operation.

What causes the Worcester Bosch C1 fault?

This fault occurs when the boiler's control board detects that the internal fan is spinning slower than the required safety threshold. The most common reasons are a build-up of dirt within the fan mechanism, a blockage in the air supply tubes, or the motor itself failing after years of use. Because the fan cannot effectively push exhaust gases out of the flue, the boiler shuts down as a vital safety precaution.

This fault is slightly more common in winter as fans often work harder during cold spells, which can cause older, weakened fan motors to finally seize or fail.

Typical repair cost £150-300 (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 C1 fault code

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

Source

Worcester Bosch C1 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