Your boiler has stopped working because it either cannot detect a flame or the internal drainage pipe for waste water is blocked.

Flame Failure or Blocked Condensate Drain

What causes this fault?

This fault occurs when the boiler tries to light but fails to detect a steady flame, causing it to shut down for safety. The most common reasons are a build-up of carbon on the sensing probe, a failure in the gas delivery, or a blockage in the pipe that carries waste water away from the unit.