High
A8 (361) on Worcester Bosch Greenstar 12i System

Your boiler's internal computer chip does not match the control system it is plugged into, preventing the unit from starting correctly.

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 invalid The inserted HCM does not correspond with the control box or HMI type.

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

A8View →E9View →

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