Your boiler's main control board has suffered a communication failure or internal electrical fault, meaning it can no longer send instructions to heat your home.

Main PCB fault

What causes this fault?

This fault occurs when the boiler's internal computer, the PCB, loses its ability to communicate with the gas valve and other vital components. The most common reason is an electrical short-circuit or a component failure on the board itself, preventing it from safely controlling the ignition sequence. Think of it as the brain of the boiler losing its connection to the rest of the system.