High
C4 237 on Worcester Bosch Greenstar i

Your boiler's computer system has encountered a critical communication error and can no longer safely operate the heating or hot water, requiring professional repair.

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

Control box or the HCM is defective.

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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