i wonder if u could shed light on a problem,the boiler is glow worm in a downstairs cupboard with the hot water tank sat next to it and what looks like a 3 port valve there is also has a pressure tank and a water tank in the loft.it appears gravity takes the water up the tank but i have no hot water pressure when drained downed to fit news rads.build up pressure to 1 bar tnk full checked for air locks but now stuck many thanks if u can help 