b3 High

Worcester Bosch b3 Fault Code

Also written as B3 — same fault.

The Worcester Bosch b3 fault code means: your boiler's computer is experiencing an internal communication failure, which means the system cannot safely operate and requires professional intervention.. It appears on 6 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: Data error Replace control board.
Typical repair cost £300-500 (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 b3 fault code

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

Source

Worcester Bosch b3 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