Somewhere amongst the pipework in or very near the boiler will be a 'filling loop' which connects the mains cold water pressure to your boiler system. On my (old) system I have to connect the loop to two valves and then open them both to repressurise the system, then turn them both off and disconnect the loop. On modern systems the loop is often built in and a single valve or key is used to allow mains pressure into your system - when the pressure is correct you simply turn it off again. Have a look for a short pipe connecting two other pipes with a valve in the middle. Hope that points you in the right direction!
Richard, December 2008
