hot water in cold storage tank

[Sydney Cistern]

How come our cold water storage tank keeps overflowing when there is nothing wrong with the ball cock.

The cold feed to the hot water cylinder, which has a coil inside, is warm right up to where it enters the cold storage tank.

I put a non return valve on cold feed but hot water started coming out of the expansion into the tank. Subsequently I put the system back the way it was.

 

[62945835]

have you fitted any mixers lately? any changes on system?
or has it always been like that?

 

[Sydney Cistern]

Its always been like that. But I'll tell you this, after you mentioning mixers, we (its a residentail home I work in believe it or not) have three mixer showers on this system, and the lot of them have never functioned properly.
The only way we can get them to work reasonably well - ie hot enough - is to gently turn on the mains fed cold tap on the sink next to each shower, enabling the hot water to come through the shower head
The showers are fed by cold mains, and hot water from a cylinder.
My boss is adamant the showers are made to accept this sort of set up, but I've always had my doubts, and he's been forever tampering with the thermostat control on them.
It's a sorry state of affairs as the hot water in the shower on occasions has reached dangerous tempratures when the sink taps were accidently turned on full blast.
As for the cold water storage tank overflowing .... we just attached a piece of plastic pipe to the overflow and ran it into a rainwater hopper, out of sight - that was two years ago!

 

[62945835]

you need non return valves on hot & cold pipe of every mixer because the high pressure mains water is going through the mixers to the cold water tank
and i would recommend you get a thermostatic mixer before you burn yourself or your kids

 

[Sydney Cistern]

Cheers for that. Will say to boss to get this done.

However, talking to a plumber mate just a minute or so ago and he says there may also be a chance that the coil in the hot water cylinder is burst.

Checked the cold feed pipe at the bottom of the cylinder and up to six feet above cylinder, and it is as warm as the expansion/draw off pipe.

Also when valve turned off on return to coil, the coil continues to heat, going by the short piece of pipe between the flow valve (electric type) and the fitting on the cylinder.

 

[62945835]

Cheers for that.

However, talking to a plumber mate just a minute or so ago and he says there may also be a chance that the coil in the hot water cylinder is burst.

yes but for the water in the cold water tank to overflow, the small tank (feed and expansion tank) would have to be at higher level than cold water tank, which i doubt it is

 

[Sydney Cistern]

What a day.... I again put a non-return valve on the cold feed to the cylinder, and next thing like before the expansion started running into the storage tank.

Originally I thought the coil was burst and the hot water entering the tank was coming from this. But I subsequently turned off the combi boiler for quite a while (no small header tank of course) and let everything go cold.

I turned off the valve on the return to the coil and then switched on the boiler. I waited to see if the top of the coil would heat. But it didn't, which scuppered my idea that there was central heating water managing to flow through the coil....via a split in the coil

I checked again in the loft, and lo and behold the expansion was still runnning - this time with cold water, as it should have - if the coil was off and therefore unable to heat the domestic hot water.

I have taken on board the idea that mixer showers (we have three) might be the problem, what with a mains cold feed and a domestic hot water feed, eg the main might be running throught the mixer into the hot.
I don't know how to check this properly. But I put my ear to each mixer to see if I could hear running water when they were not in use, and I heard or felt nothing.

By this time I was scatching my head big time.

And I am now - assuming the mixers are OK - at a total loss.

But can I say this, the storage tank in the loft has a capacity of 220litres, while the cylinder has a capacity of 240 odd litres - this can't be right surely. There is a 24 foot drop from the storage tank in the loft to the base of the cylinder

Another thing I noticed - if I havent mentioned it before, the expansion kicks off in 28 mm before reducing to 22mm halfway up to the tank. The cold feed is 22mm at the tank and goes up to 28 mm halway to the cylinder.

Any clues ..... please!

 

[Nige F]

yeah.....give me the home`s address and i`ll report it .......don`t tell me they can`t afford a safety control on their mixer showers won`t even tell my Mrs. who`s had 35 years in nursing .....

 

[Sydney Cistern]

Right, on monday I'm going to turn off the mains supply to our building off.

Then I will check and see if the tank is still overflowing. If it is NOT, then the case will be well and truly solved, and I will take great delight in either ripping out the three mixers we have or installing non-return valves on their respective mains pipes, which I now know should have been done by the cowboys who installed the showers.

And, of course, thank the mixer theorists very much for their sound advice.

 

[jackthom]

While you're still keen to experiment, how about trying the non-return valve in the hot water feed. If the problem is caused by mains pressure at the shower mixer valves that should at least stop the flow back to the cylinder.
I'd be inclined to try a pressure reducing valve on the cold main to the showers. Might solve all the problems in one.

 

[Sydney Cistern]

Yipee. success. It was a cold mains supply running through one of the showers right enough.

Non-return valve fitted on hot water supply, and job done.

Cheers for everyone's advice.

 

[Sydney Cistern]

I'm back. Can anyone tell me the dangers to health if hot water from a cylinder mixes with drinking water.

Also, we have two cylinders side by side - with one cold feed supplying both. Do they have to have separate expansions all the way up to the storage tank. Couldn't they not just be twinned a few feet above the cyclinders.