Your boiler has detected an electrical issue with its power supply or wiring, meaning it cannot safely start the burner.

Phase error

What causes this fault?

This fault occurs when the boiler detects an inconsistency with the electrical supply, specifically that the live and neutral wires may be swapped or there is a lack of a solid earth connection. The most common reason is a recent electrical repair in the home or a faulty internal component that has disrupted the correct flow of electricity. Because the boiler requires a specific electrical polarity to safely detect a flame, it prevents the burner from firing until the wiring is corrected.