Your boiler has stopped working because its internal computer has detected a communication error with the burner control system.

System fault burner control unit

What causes this fault?

This fault occurs when the boiler's main control centre loses its ability to 'talk' to the components that manage the gas burner. It is typically caused by a physical break in the internal wiring or a critical failure within the printed circuit board itself, preventing the boiler from firing safely. Essentially, the boiler has shut down because its internal systems can no longer coordinate the ignition process.