Your boiler is trying to start, but it cannot detect a flame, so it has safely shut itself down to prevent gas from building up.

No flame detected

What causes this fault?

This fault occurs when the boiler's control system tries to start the burner but cannot detect a flame after several attempts. The most common reason is a lack of gas reaching the burner or a failure in the ignition system that prevents the spark from creating a steady fire. It can also be caused by worn-out sensors that fail to tell the boiler that a flame is actually present.