Your boiler has detected an electrical wiring issue where the power supply wires are crossed, preventing it from safely lighting the flame.

Flame detection error – line and neutral reversed

What causes this fault?

This fault occurs when the boiler detects that the electrical supply wires—the Live and Neutral—have been connected to the wrong terminals. It is most commonly caused by recent electrical work in the home or an incorrectly wired plug or fused spur that provides power to the unit. Because the boiler cannot safely monitor the flame with reversed polarity, it will prevent the system from firing as a safety precaution.