BoilerFaultCodesWorcester Bosch 306 V Fault Code
Also written as 306V — same fault.
The Worcester Bosch 306 V fault code means: your boiler is still detecting a flame even after it has tried to shut off the gas, which is a safety conflict that requires a professional inspection.. It appears on 10 Worcester Bosch models in our database.
Technical description: Flame signal after closing the fuel supply – the air/gas ratio control valve might need replacing
What causes the Worcester Bosch 306 V fault?
This fault occurs when the boiler's internal sensors continue to detect a flame even after the gas supply should have been cut off. The most common reason is a gas valve that has become stuck open or a faulty electrode that is incorrectly reporting a flame to the control board. Because the boiler cannot guarantee it can stop the flow of fuel, it shuts down immediately as a critical 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 306 V fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch 306 V 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