I have a very similar fault, but this only happens on the central heating side, not on the water side. By doing some very basic fault finding, it turns out to be the flow switch. how to check it (I am not qualified in any way on boilers, but am an electro mechanical engineer). isolate from the mains, dont just switch it off on the front. remove the white cover, and then drop the control panel down. remove the plug with 2 red wires going to it, and using a paper clip, short out this connector (its not ideal, but is low voltage), secure it away from any metal (tape it to other wires), and then switch the mains on. switch the boiler on, and test the heating. Mine now works perfectly, although i will be replacing this switch. for info, it may not be the best boiler, but mie has now been working for 12 years, and this is the second fault it has had, the other way a 3 way valve failure.
Paul
January 2010