High
9U 233 on Worcester Bosch Greenstar 12i System

Your boiler's internal computer is failing to communicate with its memory chip, meaning it cannot start because it has forgotten its specific configuration settings.

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

HCM (Heat Control Module) - Problem with the code plug (faulty or not connected)

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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