Your boiler has detected a serious internal problem with the gas burner system, causing it to shut down for safety.

Burner Injector – Natural Gas Stereomatic, Type 7, Rs1/8 4.95mm

What causes this fault?

This fault occurs when the boiler detects an unexpected signal from the burner, often suggesting gas is present when it shouldn't be or a sensor is malfunctioning. It is usually caused by a failing gas valve that isn't closing properly or a faulty set of electrodes failing to monitor the flame correctly. The system shuts down immediately as a safety precaution to prevent unburnt gas from building up.