Give Mark (trackdayjunkie) a tinkle, he should be able to help.
IIRC these had an issue with the circuit boards but that was a few yrs ago, would have thought they’d fixed that particular issue by now.
I could start spouting off all the things that you could try or all the things that could be the fault but chances are will be miles out so best get professional help.
Thanks Mark for you help, I have to get some one out to look at it, I will have to run it on test for now, I followed the wires in to the boiler and they split up to two different points, and im not sure which is for the thermostat, thank again,
there are many reasons why your boiler would be doing what it is, however before calling in an engineer give Potterton Service a ring, as the boiler may have more than one years guarantee .