watertank overflowing

[wd1980]

The water tank above the hot water cylinder in my bathroom is constantly dripping out the overflow into the garden.
I have changed the ball cock and the arm mechanism to try and stop the leak.

When you look into the tank there doesnt seem to be a drip filling it. I have moved the ball cock as low as posible but the water level seems to go above it. Its fine for a few hours but then starts again, i'm filling about 4 buckets of water a day from the pipe outside.

What do i need to do!?!

 

[xr4x4]

your tank is filling up from below. i.e the supply pipes to your hot and cold water (depending on the setup you have)

do you have a boiler? is there a separate smaller tank in the loft supplying it? or is it a sealed system with a pressure gauge/red tank?

 

[wd1980]

There is a tank in the loft and a boiler in the kitchen. The problem started after we had drained the system a few times whilst fitting new radiators.

 

[TonyW2]

Is the overflowing tank the small feed & expansion tank that supplies the central heating?
Do you have a large cold water supply tank?

(The large one may feed the c/h tank or both may have feeeds from the cold supply pipe)

Are you certain the ball cock is effective? (Try tieing it up firmly)
Does the large one continually fill whilst the small one is overflowing?

If the answers are yes to all, then then the large supply tank is feeding into the hot water tank and a "split" inside this on the heating coil is allowing water back up and into the small feed/expansion tank. Hence it overflows.