Your boiler has stopped working because it cannot confirm that a flame is burning safely, leading to a complete shutdown for your protection.

Burner in fault position. Internal fault. Check the flame monitoring (ionisation electrode and lead).

What causes this fault?

This fault occurs when the boiler's control system cannot detect a steady flame after the ignition process has started. The most common reason is that the sensor responsible for 'seeing' the flame is either dirty, worn out, or damaged, causing the boiler to shut down as a safety precaution. In some cases, it can also be caused by an inconsistent gas supply or a failing electronic control board.