There should be a valve that looks like the one that controls the flow to the washing machine / dishwasher but maybe without the plastic lever. it will be on one of the water pipes that connect to the system. On mine this is linked by a metal flex hose to the system. turn slowly to increase pressure and the pressure dial should rise. Careful not to over pressure - follow the instructions (probably 1 to 1.5 bar)
Ian Rocky, March 2008