Your boiler is lighting but cannot detect that the flame has been lit, causing it to shut down shortly after for safety.

Burner extinguishes after 10 seconds (Flame failure).

What causes this fault?

This fault occurs when the boiler's internal sensors fail to confirm that a flame is present, even if you can see it lighting briefly. The most common reason is a worn-out sensing probe that has become covered in carbon soot or a faulty control board that is no longer 'listening' for the flame signal. For safety, the boiler shuts down immediately because it thinks it is leaking unburnt gas.