BoilerFaultCodesWorcester Bosch FB365 Fault Code
The Worcester Bosch FB365 fault code means: your boiler has detected a potential internal gas leak during its safety checks and has shut down to keep your home safe.. It appears on 1 Worcester Bosch model in our database.
Technical description: Gas valve EV1 leak test failed
What causes the Worcester Bosch FB365 fault?
This fault occurs when the boiler's internal safety system detects that the gas valve is not sealing correctly and is allowing fuel to seep through even when it should be closed. The most common reason is a mechanical failure within the gas valve itself or a fault in the main control board that incorrectly monitors the valve's position. Because this involves the integrity of the gas supply, the boiler shuts down immediately to prevent an unsafe build-up of gas.
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 FB365 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch FB365 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