Help! Advice needed??

The over flow from our loft tank always leaks after hot water is used, we have two tanks in the loft and the smaller one is the one overflowing, the ball valve isn't leaking and the ball iself is intact but it does tend to be 80% submerged I have bought a new valve but before I change it is there anything else to check? (im not convinced that chaging the valve is going to do it)

Any ideas??

If the float ball was submerged to 80% and had no water in it then the float switch's faulty and needs to be replaced. Good luck, Tom

Thanks Tom... do you mean the ball valve? (long brass thing that the ball screw into)

Thanks Tom... do you mean the ball valve? (long brass thing that the ball screw into)
Yes! It controls the water level in the tank. Replace it! Good luck, Tom