b7 (257) High

Worcester Bosch b7 (257) Fault Code

Also written as B7257 — same fault.

The Worcester Bosch b7 (257) fault code means: your boiler's internal computer is malfunctioning and cannot communicate with the rest of the unit to operate your heating or hot water.. It appears on 4 Worcester Bosch models in our database.

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 HCM is defective.
Typical repair cost £250-450 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Worcester Bosch models that show the b7 (257) fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Worcester Bosch b7 (257) fault code information on this page is sourced and cross-checked against the official Worcester Bosch service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026