Your boiler has stopped working because it has lost a secure electrical connection to the valve that controls the gas supply.

Check the electrical connections of the gas valve.

What causes this fault?

This fault occurs when the boiler's internal computer can no longer detect or communicate with the gas valve. The most common reason is a loose or damaged wiring connection between these two parts, or an internal electrical failure within the valve itself. Without this secure link, the boiler cannot safely control the fuel supply and must shut down.