baxi combi 80eco?

Hi I have a baxi combi 80 eco boiler. The system preasure was too high on examination but has now been bled and the water preasure is now correct according to the manual. The central heating works on both timer and On as does the hot water. The preasure guage does not increase when operating yet the system works. When off the demand for hot water does not cause an ignition or the system to function, subsiquently the water can only be obtained with the heating running. Can you suggest anything we can try