Your boiler has detected a specific internal electronic fault with the valve that controls the gas supply, meaning the appliance cannot ignite safely and will remain shut down.

Gas Valve – Propane Dungs BM771 SL 040

What causes this fault?

This fault occurs when the boiler's main control board loses communication with or detects an electrical failure within the gas valve assembly. The most common reason is an internal component failure inside the valve itself, which prevents it from opening to allow fuel into the burner for ignition.