Overflowing cold water tank

7 Apr 2004
Reaction score
United Kingdom
Hi, this is my first post and I would be grateful for any advice.

My cold water tank has been overflowing intermittently for the last few weeks. I have had:

- a new ball valve fitted - that night the tank overflowed again;
- new hot water cylinder - two days later the tank overflowed;
- yesterday, the plumber came back and bent the arms of the ball valves in the cold water tank and in the feed and expansion tank. 5 hours later the cold water tank overflowed again.

I'm getting very frustrated and the plumber is I think at a loss. Does anybody have any ideas please.

Sponsored Links
If he changed the ball valve the plumber must have thought that the water was coming in the mains cold water inlet pipe that the ball valve is attached to, and the ball valve wasn't stopping the flow of water

If he changed the hot water cylinder was that because he thought there was a leak in the coil in the cylinder and water was rising up into the cold water tank?

If he bent the arms of the ball valve he must have gone back to his earlier conclusion that the water was coming in the cold water mains inlet pipe and that the ball valve wasn't stopping the water coming in before reached the overflow

I would have thought that he could establish whether the ball valve is stopping water coming in by watching the cistern as it fills up but it seems that he isn't sure and thats why he bent the arms.

Now you have a new hot water cylinder you know that the water isn't coming up into the cistern/tank via a hole in the coil in the cylinder. Unless the new cylinder has a hole in the coil as well

If there was a hole in the coil the water levels in the cold water tank and the feed and expansion tank would be the same. Ideally the feed and expansion tank should be below the water level of the cold water tank so that if there was a hole in the coil in the cylinder then water would be overflowing out of the f & e expansion tank overflow.

So you could have a look at the feed and expansion tank and the cold water tank and see where they are in relation to each other. The water levels in each shouldn't be the same as each other. If they are that suggests that the problem is with the coil in the cylinder (which shouldnt be occurring if it is new)

Also you could drain off some water from the cold water tank and then see whether the ball valve completely stops the water before it reaches the overflow (by turning off the mains stopcock and running some taps to empty out the cold water tank then turning on the mains stopcock again). If not then the problem is with the ball valve.

Apart from those two things I dont know what else could be causing the problem. One other thing which I will say just as a longshot and which I don't mean to offend you or your plumber by saying. Are you sure that the water overflowing out the pipe is from the cold water tank and not from the WC overflow?
Thanks for replying.

I think the plumber initially thought that it was the ball valve - seemed the most likelyand the least expensive and he later bent the arm for a lower water level even though there was no water coming in from the mains after it closed off the inflow.

I think the problem with identifying a solution has been that nothing happens immediately the plumber has done some work. It started about 5 hours after he left 2 days ago; I turned the water off that night; no overflowing at all yesterday; woke up this morning to find it had started again during the night.

I live in a flat and the f&e and cold water tanks are almost at the same level with the f&e being slightly higher. The plumber turned off a tap from the f&e tank to the (presumeably) cold water tank to see if the water levels would level out over a few days between the two tanks. In fact, the f&e tank just about drained dry (almost lost the central heating pump) before I turned the whole thing off apart from a lot of sludge which presumeably is now in my radiators.

The plumber did think that the coil in the hot water cylinder had gone and although that may not have been the cause of this problem, I'm not cross that that's been replaced as some of the connections were almost completed rusted through.

The day before these problems started I'd just had a new WC installed and I did think that may be the problem. However, the new loo overflows into the pan.

Thanks again for your reply.
you might check the mains water is not backfilling into tank through crossed pipes or a need for a non-return valve
Sponsored Links
have you had any other work done new taps for instance
Hi Billy
I only had a new loo installed before the overflowing started. I've since had a nerw hot water cylinder.

The loo was connected to the same water supply as my shower and allowed for water to come in from below the cistern.. Jim disconnected the inflow at the side of the inflow.
Been a while and have had the problem ever since.

Plumber spent all morning checking out the source of problem and discovered that it is a faulty kitchen mixer tap - crossover of hot and cold water.

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Sponsored Links