Your boiler has detected an internal fault that is preventing it from operating, and it requires a professional inspection to identify the specific issue.

Boiler fault. Call engineer.

What causes this fault?

This fault occurs when a safety sensor detects that the metal housing around the burner is reaching dangerous temperature levels. It is usually caused by a lack of water flow through the heat exchanger or a build-up of debris blocking the internal ports, which prevents heat from being carried away quickly enough. In some cases, the sensor itself may have failed or the wiring has become damaged due to the high heat environment.