How do I increase water pressure in Worcester Bosch 24 cdi?

How do I increase the water pressure on my Worcester Bosch 24cdi, we have a white plastic 'key' we were told to put in the bottom and turn but it doesn't seem to do anything?
Karen Covill, December 2005


done
next to where the white plastic key inserts into the boiler theres a grey knob when you insert key you also need to turn the grey knob ,repressurise the system to around 1- 1 and a half bar then turn the knob off and remove the key

mike, December 2005
link Click here to see other fixes for Worcester.