how can I increase the pressure on my HE924.BSN?

I have a Worcester heat systems 9.24 Electronic combi boiler Product Code HE 924.BSN.
The pressure keeps falling below 1.
how do I maintain oressure between optimum 1-10.
Also unless the central heating system is on the hot water system does not work.
Are these issues related and how do I get the best out of this system.
i am based in the Newcastle area.
Thanks