I have a leaking overflow that stops when the hot water is run off. I've looked at the tank in the attic and the ballcock is almost completely covered by water.

ruth, June 2010

If the ballcock is OK, it could be something simple like a puncture in the ball which has let it fill with water and sink ! (or a leak in your hot water clinder.[internal])

davidj, September 2011

if you run the hot water tap , to get the water level in the tank to drop below the ballcock arm , when your doing this , you will need somebody to help you, as you will have to hold up the ballcock arm ,wile the tap is running, and when the water level has droped under the arm, say 6 inches, you can get them to turn the hot tap off, now look at the little ajuster nut on the end of the ballcock arm , turn it clockwise, this will control how high the tank will fill , now if the adjuster nut, is all the way anti clock wise and the water is still comming out , then you need to replace the ballcock arm , with a new one , not a hard job to do once you have knocked the mains off , unscrew the old one and replace it with the new one , trun water back on , and adjust the nut to the level your happy with ,,

marl, June 2010