Well, 5 visits, several hours of workman trime, 4 weeks and a few hundred pounds later, my boiler has a new pump,m new valves, a new PCB, and will soon have new temperature sensors. Hopefully it will then work properly.
Currently I obtain hot water by opening the front of the boiler and wiggling one of the temperature sensor wires, which then causes the circuit board to realise that the water in the 'out' pipe is cool and thus starts heating teh water. This works for a variable period of 2 days to 20 minutes. Thankfully when not working correectly, the LED flkashes constantly, so it is fairly easy to tell.After 10 plumber call outs in 5 years, my admiration for the boiler manufactuirers is immense. I habve no idea what the pourchase cost was, but I feel I have paid them at least the same value in out of warranty parts, thus maintaining their income!
If only there was mains Gas into the building.