overflow from cold water tank in loft

[rorybreaker]

Hi,
We have a problem at home with water coming from overflow pipe from the cold water tank in the loft. Now i know the most common fault is the valve but its not this as its been replaced and i've seen it for myself that the valve is shut but water still overflowing out. I have done some research myself, coming from a non plumbing background and i wondered if i could have some opinions if i list the facts of what i know so far.....

-We have had a new mixer shower fitted 3 years ago and the problem has started since this
- The cold feed is mains and hot is gravity fed
- It doesn't happen in the winter when we have all radiators on. In warmer months we turn rads upstairs off, this is when the problem starts. (very old system and when hot water is on, the rads upstairs heat up)
- The mixer shower makes a constant humming noise when not in use.
- Overflow leaks all times of the day and all night until water starts getting used in the morning.
- Water in cold water tank in loft is luke warm

From my own research it seems that hot water is being returned from the mixer shower due to pressure imbalance and then sent up to cold water tank? I have read that there is a valve that can be fitted to prevent this from happening? A non return valve? What i don't understand is that if the valve doesn't let the water return, then will it have a detrimental effect elsewhere in the system as the problem of pressure imbalance will still exist but yet the valve will not allow the water to return to the tank? I have also read that a pump may help as by equaling the hot water pressure with the cold will solve the problem?

what i want to avoid is two things. Firstly the pressure from shower is minimal. We don't want to loose any pressure. Secondly, we don't want a sticky plaster fix. We have done this with things in the past and learnt our lesson that we have then had to spend further money in the future, costing more overall rather than an initial outlay at the very start.

Would really appreciate your opinions and advise. Naturally we will be getting a plumber to do the job but i want to go into this with some knowledge rather than having someone come round and telling me the only choice is a whole new system. If this is genuinely the case then so be it but i want to be sure. Thank you in advance.

 

[Best]

Sounds like mains water is being pushed through your shower valve, into the hot and will push into the copper cylinder and up the cylinder cold feed into bottom of cold water tank in loft.
A torch shone into cwt to the bottom connection will show a haze of hot water mixing into the cold water.
Your hot water is open vented and the higher pressure cold mains will simply push into the hot.
A check valve on hot pipe to shower will sort it.
Not sure why your heating system would have any relevance

 

[rorybreaker]

Sounds like mains water is being pushed through your shower valve, into the hot and will push into the copper cylinder and up the cylinder cold feed into bottom of cold water tank in loft.
A torch shone into cwt to the bottom connection will show a haze of hot water mixing into the cold water.
Your hot water is open vented and the higher pressure cold mains will simply push into the hot.
A check valve on hot pipe to shower will sort it.
Not sure why your heating system would have any relevance

That's a great help thank you. I have a couple of further questions in response to your message please.
1. You say you don't see the relevance of the heating. What would explain the reason for it not happening at all in the winter and then only starting when we turn off the rads upstairs in the summer, in your opinion?
2. What would be an avaerage cost of having one of these valves fitted?
3. Is it right that it happens all the time, even when we aren't using the shower?

Thanks again

 

[Best]

(1) Your heating system isn't directly connected to your hot and cold water. The heating system heats the cylinder indirectly through a coil pipe inside the hot cylinder, normally, so the two waters can't mix unless there is a hole inside the coil, or with combi gas boilers can have a faulty heat exchanger apparently.
Turning your rads off in the summer can cause a heating vent or feed pipe to push heating system water up into the expansion tank, if a fault in the system, or if badly designed piped.

(2) Getting a check valve fitted to shower pipe would only be an hours labour perhaps if pipe accessible.

(3) Cold water large storage tank overflowing constantly must be due to mains water getting into it somehow. Usually faulty mixer tap or shower. Or gas boiler exchanger, as I mentioned.
(Only other thing can do that is hole in internal coil of cylinder, with the small expansion heating tank higher than cwt)

 

[rorybreaker]

(1) Your heating system isn't directly connected to your hot and cold water. The heating system heats the cylinder indirectly through a coil pipe inside the hot cylinder, normally, so the two waters can't mix unless there is a hole inside the coil, or with combi gas boilers can have a faulty heat exchanger apparently.
Turning your rads off in the summer can cause a heating vent or feed pipe to push heating system water up into the expansion tank, if a fault in the system, or if badly designed piped.

(2) Getting a check valve fitted to shower pipe would only be an hours labour perhaps if pipe accessible.

(3) Cold water large storage tank overflowing constantly must be due to mains water getting into it somehow. Usually faulty mixer tap or shower. Or gas boiler exchanger, as I mentioned.
(Only other thing can do that is hole in internal coil of cylinder, with the small expansion heating tank higher than cwt)

Thanks again for the info, greatly appreciated and all makes sense.

With regards to the rads, when we have the hot water only on, the rads upstairs heat up but not downstairs. They only gets when heating is on. My theory was that in summer when rada upstairs turned off, water which is usually pushed back from shower is sent round rads instead of back to tank? Or is that not possible?

With regard to the water getting into the tank causing the overflow at all times, would the humming of the shower have anything to with it?

Thanks again

 

[Best]

The humming from the shower might be the mains passing through the shower body. It shouldn't be able to do that in theory, but shower valve could be faulty. However, a check valve on hot feed to shower should correct that.
It is a No about your idea of water pushing from shower to rads.
If water is passing through the shower, it will only go into the hot water, (not the system heating water) and will take an open, lowest point, - the hot cylinder feed pipe coming from bottom of cold water tank in loft. See if you can rule that in, or out first before you proceed

 

[rorybreaker]

The humming from the shower might be the mains passing through the shower body. It shouldn't be able to do that in theory, but shower valve could be faulty. However, a check valve on hot feed to shower should correct that.
It is a No about your idea of water pushing from shower to rads.
If water is passing through the shower, it will only go into the hot water, (not the system heating water) and will take an open, lowest point, - the hot cylinder feed pipe coming from bottom of cold water tank in loft. See if you can rule that in, or out first before you proceed

Ok all understood. Thank you again.

I wonder why it doesn't do it in the winter months?

Last question, would the hot water, being gravity fed, be restricted when going through a check valve? The flow from shower isn't great as it is. I'm worried this would restrict it further due to the way the valve works?