Had the problem at home where the overflow from the Central Heating Expansion tank was constantly dripping without the Ball Cock leaking - putting this down to the water in the Cylinder getting into the Central Heating Circiut via a leak in the coil I decided on trying an 'in-situ' fix. What I did was turn off the feed to the Cold water tank (and hence the hot water) and ran the hot taps to create a vacuum in the cylinder. I then poured some 'Leak Stop' into the Central heating expansion tank which got sucked back down into the coil - through the leak - and hence fixed the hole causing the problem..
Worked a treat.. how u like them apples fish-face!
Worked a treat.. how u like them apples fish-face!