BoilerFaultCodesWorcester Bosch B7257 Fault Code
The Worcester Bosch B7257 fault code means: your boiler's internal computer or its identification chip has developed a communication failure, preventing the system from operating.. It appears on 3 Worcester Bosch models in our database.
Technical description: The burner control unit or the KIM (boiler identification module) is faulty
What causes the Worcester Bosch B7257 fault?
This fault occurs when the boiler's main control board loses its connection with the internal memory chip that identifies the specific model and power settings. The most common reason is an electronic component failure within the circuit board or the small module that stores the boiler's unique configuration. Without this data link, the boiler can no longer safely coordinate the heating process and shuts down as a precaution.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Gas Safe Register →Worcester Bosch models that show the B7257 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch B7257 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 27 April 2026