Hi,
this boiler is frought with problems of this type, it may be the PCB, water pressure switch, or pump,
parts and support is hard to find as the company appears
to be out of operation, the service help line simply gives an alternative number, searching for parts online is getting more and more difficult,
as I understand, British Gas still has this boiler in their service list, and their homeserve packages are looking very attractive of late...
sorry I couldn't offer anything more.
Chris, January 2011