baxi 105e - high pressure?

My Baxi 105e has a pressure of between 3 and 4 - it only reduces to 3 when i turn it off. In addition to this I have no hot water, but i do have nice hot radiators!? when ive had a look at the panel - it appears that the hot water pre heat is not working - if i turn it up the heating symbol goes out and the h/w neon just flashes at me!
does anyone have any suggestions please?