I am having a problem with the pressure in my CH system,with the pressure set to 1 bar when cold, I turn on my heating and the pressure gradually increases to 3 bar and above! this is causing the release valve to open and reduce the pressure in my system once the heating is turned off! locking the boiler out and giving a code 4 on the display. I have not used the heating all year and the boiler has been fine for about 3 years.assistance would be greatfully received!