High Lockout
C1 on Worcester Bosch Greenstar 25HE

Your boiler has stopped working because the internal fan isn't spinning fast enough to safely clear away exhaust fumes.

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 senses that the fan isn't rotating at the required speed to safely vent exhaust gases out of the flue. The most common reasons are a build-up of dust and debris inside the fan motor, a mechanical seafing of the bearings, or a communication failure between the fan and the main control board.

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

C4View →C6View →A1View →

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