Overflow from cold water tank won’t stop

[footprint]

Please can anyone give me advice. The overflow from my cold water tank started dripping so I changed the complete valve and ball. I set the ball to maximum on the arm and still it continues to trickle water. Would changing the 4 1/2 inch ball to a 6 inch ball help. Any help to stop this irritating problem would be very much appreciated.

 

[ShaunCorbs]

If you lift the arm up does it stop also you did change the float also ?

 

[footprint]

Hi Shaun thanks for reply. Yes the water does stop if I lift the arm, I also changed the float so all is new.

 

[ShaunCorbs]

I would put a mark on the tank at the water level and hold the ball up is the level dropping etc

 

[footprint]

I will give that a try tomorrow. Thanks

 

[Basher]

When the ball valve begins to close, is the water level already very close to the overflow outlet? Or when it closes, is the water level way below (ie a few dentimetres) the overflow, and then over time the water level creeps up?
If the former, the float needs to be adjusted so the valve turns fully off at a lower water level. I used to adjust this by bending the brass arm down a bit, but no doubt the professionals will advise me of the proper method!
If the latter, the new valve is passing, or there is a leak into the tank somehow.

 

[Ben-gee]

If the new valve operates correctly, this could be caused by a split coil in the hot water cylinder.

 

[Ric2013]

When the ball valve begins to close, is the water level already very close to the overflow outlet? Or when it closes, is the water level way below (ie a few dentimetres) the overflow, and then over time the water level creeps up?
If the former, the float needs to be adjusted so the valve turns fully off at a lower water level. I used to adjust this by bending the brass arm down a bit, but no doubt the professionals will advise me of the proper method!
If the latter, the new valve is passing, or there is a leak into the tank somehow.

The correct way if the water level is already very close to the overflow would have been to install the ballcock at the correct height in the first place.

In practice, if the hole for the ballcock (float valve) has already been drilled too high, it comes down to what is reasonably practical in the circumstances. You could find a way to blank off the incorrect hole and start again. However, since the older-style 'Portsmouth' valves were adjusted by bending the float arm, I would suggest (at the hypothetical risk of inducing stress-fractures in the brass rod) that if you were to bend the rod this might seem to be a reasonable way of bringing the adjustment range somewhere closer to being useful.

 

[Aquarius]

Any new work recently? New tap, shower etc? Could be a cold feedback overpowering the hot backfilling the cylinder?

 

[Ric2013]

I'm assuming there is a re-enforcement plate fitted behind the valve and that the tank wall isn't bending under the pressure of the float? There should be one, but there often isn't.