Your boiler's internal computer has encountered a communication error or has failed, which means it cannot tell the boiler how to operate safely.

MAIN CONTROL BOARD (PCB): THIS FAULT MAY BE INTERMITTENT. SWITCH (OFF), WAIT APPROXIMATLEY 5 SECONDS, SWITCH (ON). IF FAULT PERSISTS REPLACE MAIN CONTROL BOARD (PCB).

What causes this fault?

This fault occurs when the boiler's main control board suffers a hardware failure or a breakdown in its internal electronic memory. Essentially, the 'brain' of the appliance has become scrambled or has stopped sending signals to key components, often due to an electrical surge or the natural aging of the circuit board's capacitors.