There will be a valve/connector somewhere with the boiler, usually with a steel protected flexible pipe. Some boilers, have their own inlet valve. You need to open that valve, very slightly, until pressure is about 1. If pressure keeps dropping, over a short time, (over months, not such a problem, but, still,) you have a leak on your heating system, find it fix it, might just need a nut tightened, but you need to get it seen to. Also need to bleed air out of radiators, valve on top edge of radiators is bleed valve, open until water comes out, then check pressure again, as opening bleed valve, will reduce pressure.
SD, November 2011
