I have a wall mounted Worcester Bosch 24 and you need a special "T -shaped" plastic key which you can get from the plumbing merchant for about £10. I then remove the cover from underneath the boiler (having switched it off!) and the you then insert the key with the "T" shaped handle downwards and pointing "east - west". When you feel it is fully inserted turn it "north -south" - this opens the mains water supply to the boiler. You then need to turn the tap to let the water into the system - this is to the right hand side of where the key is inseted. Ensure you only fill the boiler to the recommended pressure. Then make sure the tap is shut-off, turn the "T key" back to "east-west" and carefully remove it.
eatclintwood, November 2008
