Hi Going to put this in complete laymans terms... OK, If the heating's on, turn it off. Then insert the plastic valve key into hole underneath the boiler (on the collar of said hole are two symbols, closed padlock and open padlock) put it in so that the arrows on the key correspond to the open padlock. push the key right in (the second seal on the key will go a good 10mm deeper than the hole surround) and turn it anti clockwise to the closed padlock symbol. That's all you need to do with the key, next to where you have inserted the key is a plastic square topped screw, turn that a little bit anti clock-wise and you will hear the water pressurising the system, let it fill to about 1 bar then close it off again, bleed the radiators again and if needed fill the system a little more again (repeat what you have just done). Hope this is a little more help then the other useless answers :)
Big Rik, January 2010