Your boiler is failing to detect a flame after it tries to start up, meaning it cannot provide heating or hot water.

No flame after the ignition phase – electrode error, flame unstable, incorrect valve gas offset or flue gas circuit obstructed

What causes this fault?

This fault happens when the boiler's control system cannot confirm that a flame has successfully lit after trying to start. The most common reasons are a worn-out ignition spark or a dirty sensor that fails to 'see' the flame, though it can also be caused by an incorrect mix of gas and air. Because the boiler cannot guarantee it is burning fuel safely, it shuts down as a protective measure.