water pressure can be toped up via a filling loop which for a greenstar should look like a flexi silver pipe, which is often found either ontop of the boiler or inside the boxing underneith it, you must connect the filling loop to the two blank pipes with service valves on stated in the manufacturers instructions. once attached open the service valve and pressurise to 1.5 - 2 bar ( using the pressure gauge on the right hand side of the boiler control pannel. once filled shut both service valve and remove filling loop, job done. good luck!
andrew., May 2010