Thanks to all - I am very clear as to what the problem is now and understand how the leaking valve could damage the PCB, which - as you noticed puzzled me at first. The diverter valve is new, the motor has been tested (and a new one tried with no effect) and the signals to the valve are...
Agile, many thanks for the helpful comments - I agree that it's not a good idea for me to fiddle with it - I was just trying to understand because the technician was despairing! Now I have the info from you and the others I know where I am and that I do need a new board.
Bunnyman: when I...
Interesting - I don't think the first statement can be true - the original diverter only wept a little and the water would, in any case have had to travel horizontally across a 1-2 inch gap and get into the PCB box which is just a plain plastic box with no path inside it at that point. Any water...
Mine is also just over 5 years old - we had a problem with heating on all the time and called the guy to fix it. New diverter valve but not right - several visits and still not right. We now have control over the heating but the hot water doesn't work. If we call for hot water we get some...