Your boiler is trying to ignite the gas to create a flame, but for some reason, the burner is failing to light or stay lit.

Gas at burner. If burner does not light, go to section ‘F’.

What causes this fault?

This fault occurs when the boiler's control system attempts to start the heating process but cannot verify that a safe, stable flame has been established. The most common reasons are a lack of gas reaching the burner, dirty or worn electrodes that can't create a spark, or a failing internal component that cannot sense the flame correctly.