Your boiler's internal computer has developed a fault and can no longer control the system safely.

Main PCB fault

What causes this fault?

This fault occurs when the main control board's internal memory or processor fails, meaning it can no longer communicate with the boiler's sensors or valves. The most common reason is electrical fatigue or a power surge that has damaged the delicate circuitry on the board. Over time, heat exposure within the boiler casing can also cause the soldered connections on the PCB to degrade and fail.