Your boiler has detected a problem with the internal gas valve and has shut down as a safety precaution, meaning you will have no heating or hot water.

Gas safety value failure

What causes this fault?

This fault occurs when the boiler's main control board detects an electrical failure or a mechanical blockage within the gas valve assembly. The most common reason is that the valve's internal solenoid has burnt out or is no longer communicating correctly with the electronics, preventing gas from safely entering the burner.