I have had a problem losing pressure from my combi boiler system - I have to top it up on a daily basis. I have a Worcester 24i RSF. When the pressure rises There has been water coming out of the PRV pipe outside of the house ( this doesn't happen when the system is cold) I have checked my Expansion Vessel - with the water pressure at 0 Bar I pressed in the valve and no water came out- hardly any air came out either. I got my bike pump and pumped it up to around .8 Bar. When I did this the gauge on the boiler went up too, to around 1 Bar. I then tried the heating and the pressure still went up to around 2 1/2 Bar, before creeping back down - the pipe outside of the house from the PRV was still dripping. When it had all cooled down I checked the air pressure in the EV and there was hardly any air in it again!? Does it sound like the PRV or the EV or something else? Please help guys.......