Hwlo with wold water tank overflowing

[philwilliams]

Hi
Im new to this forum.
My cold water tank is overflowing.
I know it is not the ball cock as that is fine.
The issue is that the water from the hot water cylinder is backing up into the cold water tank in the attick cauing it to over flow.

When i turn the feed from the cold water tank to the hot water cyminder off, the water goes through the expansion pipe into the cold water tank. when i open that feed, it goes through the inlet pipe of the hot water cylinder into the cold tank.

In addition to this, it over flow even if the water is cold in the HW tank
does this mean i need a new cylinder?

also, as it is sealed water system, why would more water going into the tank causing it to over flow? i dont know why water would go into the hot tank if it is full!

any help appreciated.
thanks
phil

ok, i think it is the ball cock now, Having turned the water off to the cold water tank, the leak has stopped.
does the water from the hot tank feed into the cold tank through water getting hot and expanding etc on a regular basis?

I have changed the ballcock but the same thing is happening.
The water temperature in the cold water tank is warm so definately coming from the hot water tank.
would the issue be the coil?
the query i have is, if all the hot water from the HW tank is going to the cold water tank, is the HW tank being filled up with cold. i dont know why it would over flow if they are both recycling the same water?

[justlead1]

Hi Before investing in a new cylinder, check that there is no cross flow in the plumbing system, mixer taps, mixer shower etc. Also check that the filling loop to the sealed heating system is not permanently open. (as this would account for the problem if the coil within the indirect cylinder were at fault. (If the main supply pressure was less than 3 bar it may not appear via pressure relief valve) Good Luck

[Bernie2]

If after checking for cross flow on things such as mixer taps, showers, washing machines (unlikely, but possible) dish washers (same).

Then what sort of central heating system do you have?

Do you have a combi?

System boiler?

Conventional boiler?

Do you have one cold tank (cistern) or one big and one small one?

Is the small cold tank higher than the big one? Does the water run into it all the time?

Loads of questions and possible ways things could be arranged that is why its not so easy to give a clear yes or no answer to your questions.