Your boiler has detected an internal communication problem between its electronic components and is unable to fire up.

check the wiring harness

What causes this fault?

This fault occurs when the boiler's internal computer chips lose the ability to talk to each other through the electrical circuitry. It is usually caused by a loose connection in the internal wiring or a mechanical failure within the main control board that prevents signals from being sent correctly. Because the boiler cannot verify that all systems are safe, it shuts down as a protective measure.