Look underneath the boiler. There is usually a 'semi built' in filling loop. The 2 pipes to the right are joined together by a looped pipe with 2 valves on it. This pipe runs to roughly half way across the bottom and back. The logic is that if the valve is in line with the pipe it is ON and across is OFF. Open one valve and then when you open the second the pressure will increase. Shut the valves when you have reached 1 - 1.5 bar.
The fact that you have to do this could indicate a leak in your system or perhaps a pressure vessel fault.
PS It is possible that a conventional filling loop has been fitted but these generally come with the kit I have mentioned above
Slugbabydotcom, May 2008
