Low Pressure Problems on Worcester 28i Combi Boiler?

I have recently moved into a new property but the Worcester 28i Combi boiler seems to have problems with pressure. The boiler works but the pressure has never gone above 1 and so is always below the recomended pressure.

If I need hot water and the contiol is on the hot water only mode the pressure is not enough to provide hot water, unless the central heating control is set to on, then it is ok.

I spoke to a friend and they recomended that I locate the pressure release valve and turn it until the pressure built up. Problem is it will only turn one way and the pressure has gone down even more now.

Have I done the right thing but not enough or is there something else I need to do. I can't afford over £100 to get someone out just to turn the correct knob.

Any help would be appreciated.

Thanks

Dan