Your boiler’s main computer brain has developed an internal electrical error and can no longer control the heating system safely.

Internal fault (PCB)

What causes this fault?

This fault occurs when the boiler's main control board suffers a critical internal electrical failure, meaning it can no longer communicate with the sensors or fire the burner safely. The most common reason is age-related wear on the board's circuitry or a small power surge that has damaged a sensitive component. Because the 'brain' of the boiler is compromised, it shuts down entirely to prevent any unpredictable behavior.