if you have a combi/sealed system boiler there will be a filing link or valve which is used to pressurise the central heating system circuit, usually this is found underneath the boiler itself and can look like a braided pipe with a small lever, this lever if turned slightly will let mains water into the central heating circuit raising the pressure, alternatively there may be a water lever valve which does the same thing. If your pressure drops on a regular basis you may have a leak on your central heating circuit which will need to be investigated.
Mark, May 2010
