If the mains power, fuse & selector switch/wiring are all OK � the service instructions says change the PCB.
I would take a look at the PCB to see if it has an on board fuse � otherwise you are looking at an expensive fix, when you add to the cost of the PCB, the call out charge.
Just a point of clarification on my above post � I was referring to the mains fuse, integral to the mains terminal block within the boiler, and not a fuse external to the boiler.