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My cold water tank is filling up. Initially I though it was a faulty ball valve but tested it and it is working fine. So I drained the tank to see where the leak was coming from and discovered that there seems to be a slight back flow from the cold water pipe that fills the hot water cistern downstairs. This is filling the tank up so that it is constantly at the level of the over flow pipe.

Any thoughts on preventing this from happening?

Is this the small central heating tank over filling??

Do you have two header tanks? Large and small.

IF yes to both then the hot water cylinder coil could be perforated which unfortunately means it will need replacing.

Thanks Plumb Bob.

There are 2 tanks, one large and one small, and it is the large tank that is over flowing.

Do you think this is still the coil?

Will Curphey wrote:There are 2 tanks, one large and one small, and it is the large tank that is over flowing.

Do you think this is still the coil?

It would depend on the water levels in the two tanks. Generally it works the other way because the water level in the larger tank is higher so it ends up in the smaller lower tank. If in this case the higher tank is overflowing, then it can't be the coil as water does not run up hill!

If we cross that out, the next favourite is a faulty mixer tap where the high pressure cold water is crossing over to the low pressure hot.

I have a feeling that the little tank is higher than the larger one (it's on a platform) but will need to double check when I get home after work.

Thanks for the help so far