C1 High

Worcester Bosch C1 Fault Code

The Worcester Bosch C1 fault code means: your boiler has stopped heating because the internal mechanism that pushes air through the system is not spinning fast enough to allow for safe combustion.. It appears on 21 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 low.

What causes the Worcester Bosch C1 fault?

This fault occurs when the boiler's control system detects that the internal fan isn't rotating fast enough to safely expel exhaust gases. It is usually caused by a build-up of dust on the fan blades, a failing motor, or a communication issue from the main control board. If the fan cannot reach the required speed, the boiler will shut down as a safety precaution to prevent fumes from staying inside the unit.

Typical repair cost £200-400 (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 31 August 2026