Last weekend the boiler lost pressure and shut itself down, after resetting the thing and filling it to a pressure of 1bar it fired back up and seemed to be working OK. The following day it had lost pressure once again and wouldn't fire up, so I drained the boiler checked the pressure in the expansion vessel (should be at 0.5bar according to the destructions) which appeared to be about right, refilled it and fired it back up. About 5 minutes later I went outside and noticed water dripping from the discharge pipe, so I shut the boiler off and drained it again, removed the PRV cleaned it out (wasn't expecting much of a cure but thought it was worth a go for a temp. fix), put it all back together and all seemed well with nothing leaking. The following day the pressure had dropped back down to 0.5bar and it wouldn't fire up, so again I refilled it to 1bar and off it went, but this time water was running quite quickly from the discharge pipe. So I thought it needs a new PRV, so I ordered a genuine Glow Worm PRV and installed it last night after work. Filled the boiler fired it up and it ran lovely, jobs a good'en I thought. However after it had been running for around 4 hours (no leaks) with the heating set to 20°C (boiler was reading a constant temp. of 59°C) I shut it all off and noticed the status LED on the boiler flashing green and the system pressure was reading 2.8bar.
Now I'm no boiler expert, but seeing as the PRV cracks at 3bar, a system pressure of 2.8bar seems a little too high for my liking? What would cause the pressure to rise so high, or is this normal? When I got up this morning the pressure was reading 0.9bar.