High Lockout
B7257 on Worcester Bosch CDi Classic

Your boiler's internal computer has developed a fault and can no longer communicate with the main control system.

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 heat control module HCM) is defective- the HCM and control box connections need to be checked

What causes this fault?

This fault occurs when the boiler's internal processor fails to read the data chip that tells it how to operate safely. The most common reason is an electronic failure within the Heat Control Module or the main circuit board, effectively leaving the boiler without its 'memory' or operating instructions.

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

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