Your boiler has detected an internal electrical communication error or a wiring issue, which is preventing it from running safely.

Wiring fault

What causes this fault?

This fault occurs when the boiler's internal components stop talking to each other correctly, effectively causing a breakdown in communication between the electronic 'brain' and the sensors. The most common reason is a loose connection in the internal wiring or a specific electronic failure on the main circuit board that prevents it from sending commands.