no hot water and pressure valve is on red and water is leakiing outside?

I have installed a baxi combi 105e; serial MBKo451 compno 2478726/00.

My combi boiler is playing up. For months the hot water light is off and I am not able to get hot water except when I switch to boiler and central heating. I also noted a week ago that the pressure valve/indicator was low, so I turned the pressure valve on, it went straight into the red zone and has not levelled back to the normal pressure. A week ago the boiler started to leak wate outside. WHATS WRONG!!