try replacing the diaphragm in the pressure differential assembly. they perish and let water in on both sides of the d/phragm, also the pin sometimes sticks with scale. isolate the cold inlet to the boiler (second black tap lever from the right) on the jig and open a hot tap to release some pressure. the front of the pressure diff is held by screws around the outside edge, undo these and put the new diaphragm in (clean the pin aswell)
notsayin
September 2008