High Lockout
235 on Worcester Bosch CDi Classic

Your boiler's internal computer parts are unable to communicate with each other due to a software mismatch.

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

Incompatible heat control module (HCM) software versions – control box needs latest software

What causes this fault?

This fault occurs when the boiler's internal computer brain and its specialized memory chip are unable to talk to one another because they are running different software versions. It usually happens after a repair where a new part was installed that isn't compatible with the existing system, or if a power surge has corrupted the digital handshake between the components.

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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