You can reduce the water pressure by bleeding water out of the radiators in the usual manner, but it will take a while as you may well have to remove a pint or two. The pressure should not increase in a boiler, but it will do if the 'filling loop' valve isn't fully closed. With the central heating on, expect the pressure to increase a little, and if the pressure fluctuates then its usually due to the expansion vessel inside the boiler being down on air pressure. Hope this helps!
John, March 2008
