go on the worcester/bosch web site look for your model then look for how to refill/repressurise system ,Turning the tap you are turning only opens the supply tap BUT does not fill the system, there is another tap to OPEN hence do the search and see the instructions and location of the bits you need to twiddle .
(I've been there and had a look good instructions and pictures)
As the saying gos a picture(s) paints a thousand words
explanation
wirecutterman
November 2009