High
9U on Worcester Bosch Greenstar CDi Compact

Your boiler's internal computer is failing to recognize a vital communication chip, which is preventing the heating system from operating safely.

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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Related fault codes

9AView →

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