Your boiler has failed to keep the flame lit and has locked itself out for safety.

Ignition fault (lockout) Went out when lit

What causes this fault?

This fault occurs when the boiler successfully lights but then immediately loses the flame signal, causing it to shut down for safety. The most common reasons are worn-out sensors that can no longer 'see' the flame or a gas valve that isn't providing a steady enough flow of fuel to keep the burner lit.