my arrison combi boiler runs to the max pressure?

The pressure should be between 1 to1.5 when the boiler is cold and nothing running. No more than this. The pressure increases in proportion to the temperature, so the higher you turn the temp control for the heating the higher the pressure will go until it reaches a max around 3. The pressure relief valve will release pressure and then close itself off(in a perfect world ).
If the pressure rises rapidly there may be a deeper problem but just try setting it as you have to around 1 bar and turn your temp control down. if it settles down adjust temp control up in small increments till you reach a happy setting. Same with hot water.

T.H.S
April 2007