We have a combi boiler which is now showing between 2.5 and nearly 3 bar. The pressure release valve is constantly dripping outside. The boiler is all working fine, ie heating the water when needed etc. I also have the central heating to come on every day for about 20 minutes just to keep the central heating going over the summer. The boiler was serviced in February and all was ok. The lights on the front of the boiler are showing the boiler is working fine. I can't hear any funny noises when the boiler is working. I have released the pressure by bleeding a radiator and have put it to 1 - 1.5 bar, but after about 24 hours, it has gone back up to 2.5 to 3 bar. What could be the problem? Any help would be appreciated.