High
C4 on Worcester Bosch ZB 7 27 HE

Your boiler's fan is stuck running continuously, which means the system cannot correctly regulate itself and has detected a fault in its cooling or venting process.

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 does not switch off.

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

C1View →C6View →

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