BoilerFaultCodesWorcester Bosch 1-b8 Fault Code
Also written as 1B8 — same fault.
The Worcester Bosch 1-b8 fault code means: your boiler is struggling to control its power level correctly, which may lead to it shutting down to prevent damage.. It appears on 1 Worcester Bosch model in our database.
Technical description: Actual burner modulation: Actual burner modulation.
What causes the Worcester Bosch 1-b8 fault?
This fault occurs when the boiler's internal computer is unable to accurately communicate with the gas valve to throttle the flame up or down. It typically happens because the electronic signals sent to regulate the fuel flow are being interrupted or misinterpreted by a failing control board. Without the ability to precisely control its power level, the boiler shuts down as a safety 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 1-b8 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch 1-b8 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