If you have an instruction manual read it - if not, these comments are generic to pressurised system. Somewhere in or very near your boiler (usually just under the boiler casing) you will find a 'filling loop' this will connect cold water mains pressure water to your sealed pressurised system. On some boilers the loop is permanent and you simply turn a key/valve/tap in order to increase pressure. On other systems you have to connect a braided steel flexi hose to two outlets one mains and the other heating. Once the loop is screwed on to both 'taps' you can open both valves until the presure is correct.
Make sure the system has cooled down before you do this. After you have restored the system pressure to its correct level you can bleed any radiators you want to remove air - but remember this will have the effect of lowering the system pressure so you may have to top up again (depending on how much air you bleed off). Hope that all makes sense!
Richard
January 2009
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