High Lockout
C1 on Worcester Bosch ZWB 7-25

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.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

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 this 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.

Engineer required

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Related fault codes

C6View →F7View →

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