Your boiler is failing to detect a flame, so it has safely shut down to prevent the release of unburnt gas.

Flame detection fault. Check flame sensing electrode connections. Check for a short circuit to the electrode or wires.

What causes this fault?

This fault occurs when the boiler's control system cannot confirm that a flame has successfully ignited inside the burner. The most common reasons include a worn-out sensor that monitors the fire, a blockage in the gas supply, or an electrical issue preventing the ignition spark from triggering.