As you read this if your boiler is a combi consider how has the pressure gone high, has it sneaked up there over time or risen there rapidly.If it is the latter then you may have issues within (a)The heating exchanger.(b) Your top-up v/vs and hose passing and letting water into your system.However to bring back to 1 to 1.5bar best to have the boiler off.Go to the nearest rad and vent off into a container water from the rad, have someone observe the gauge and stop venting at the 1bar reading. Make certain the top-up v/vs are shut, put a demand on your boiler from your domestic hot water tap check that the system pressure does not rise back up to 3 if it does then your exchanger is leaking.
Guytawe, May 2010
