I have noticed my pressure gauge reading 0.3 bar so i tried to raise it with the filling loop key, once I inserted and locked it in place i turned the grey pressure nob anti-clockwise and could hear the water rushing around the system but the needle didn't move on the pressure dial so after 10 secs or so I closed the filling loop valve and removed the key. I checked it again 10 mins later and it had gone up to around 1 bar and over the course of about 30-60 mins it was now just over 2 bar. It settled around 2.5 and over another 30-60 mins i noticed it had dropped back down to 1.5 bar then a day later it was back down to 0.5 bar! what is wrong with it? I have no heating problems and have hot water on demand. I can also see no leaking water or hear any funny noises. Please help I am worried this is gonna cost me alot of money to fix.