Your boiler has detected an electrical connection issue with the gas valve, meaning it cannot safely ignite to provide heating or hot water.

Fault: Gas valve assembly. Gas valve assembly not connected or it is connected incorrectly, short circuit in the cable harness

What causes this fault?

This fault occurs when the boiler's internal computer loses electrical communication with the gas valve, which is the component responsible for releasing fuel into the burner. The most common reason is a loose or damaged wiring connection between these parts, though it can also be caused by a complete electronic failure within the gas valve itself.