Warm water in loft tanks

[sparer]

Hi,

I noticed that the overflow on our loft storage tanks were letting water by.

I noticed that the water in the tank is quite warm and that the cold feed pipe going to the hot water cylinder was warm too. These are two 25 gallon tanks so it would take quite a volume of hot water to make these warm. Should I put a double check valve on the cyl feed it to prevent it back flowing?

 

[Madrab]

Absolutely not - If the cold feed is warming up and expanding back up into the cold water cistern (CWSC) then I'd be checking out the safety vent and ensuring everything is free and unrestricted from the cylinder up to CWSC's. I'd also check any monobloc mixer taps, where the cold is mains fed, as that may be crossflowing and backing up into the cylinder.

If a check valve would be used anywhere it would be at the troublesome tap if that was found to be the problem though, check valves on gravity fed supplies can impeded flow.

 

[Daveydub]

I'd also check any monobloc mixer taps, where the cold is mains fed, as that may be crossflowing and backing up into the cylinder.

And of course any shower valve or blending valve

 

[sparer]

Absolutely not - If the cold feed is warming up and expanding back up into the cold water cistern (CWSC) then I'd be checking out the safety vent and ensuring everything is free and unrestricted from the cylinder up to CWSC's. I'd also check any monobloc mixer taps, where the cold is mains fed, as that may be crossflowing and backing up into the cylinder.

If a check valve would be used anywhere it would be at the troublesome tap if that was found to be the problem though, check valves on gravity fed supplies can impeded flow.

Would crossflow on mixer taps or shower valves occur when they are not in use? The taps and shower valves are newish <3yrs old. I was here on my own this morning when I noticed the overflow.

 

[Harry Bloomfield]

Would crossflow on mixer taps or shower valves occur when they are not in use? The taps and shower valves are newish <3yrs old. I was here on my own this morning when I noticed the overflow.

After the system has had a good amount of time, unused, for pipes to cool - feel and make a not of which pipes are warm/hot. That should give you all the clues you need, as to where hot water is flowing.

 

[Daveydub]

Mixer taps (including kitchen) would only be a problem when used. A shower or blending valve would not need to be in use. Do you have a shower with tank fed hot and mains cold?

 

[sparer]

Mixer taps (including kitchen) would only be a problem when used. A shower or blending valve would not need to be in use. Do you have a shower with tank fed hot and mains cold?

Yes, I do..3 of them...there's 1-ensuite, 1 in the bathroom and 1 in a small cloakroom. Is it possible to identify which one might be faulty. They are all bar valves.

 

[Harry Bloomfield]

Is it possible to identify which one might be faulty. They are all bar valves.

Read my post #5 above.

 

[sparer]

Read my post #5 above.

Is it not the other way around though? If the cold mains feed is getting into the hot gravity feed via a bar valve, then the valve connections will both be at the temperature of the mains cold water or am I missing something?

 

[Harry Bloomfield]

Is it not the other way around though? If the cold mains feed is getting into the hot gravity feed via a bar valve, then the valve connections will both be at the temperature of the mains cold water or am I missing something?

If left with no water running through them for a while, all pipes will take on the ambient room temperature. If cold mains water flow through a pipe, then it will feel much colder to the touch. Likewise if hot water flows.

 

[sparer]

If left with no water running through them for a while, all pipes will take on the ambient room temperature. If cold mains water flow through a pipe, then it will feel much colder to the touch. Likewise if hot water flows.

Okay, thanks, that make sense. I'll have a check around based upon that.

 

[sparer]

I think it's a dodgy bar valve. I went to do what Harry suggested and luckily I went into the bathroom without turning on the light so no noise from the extractor. I can hear a slight noise coming from the valve so i'm guessing that it's letting by internally. I'll change the valve as I'm pretty sure that this will be the issue. I'll try turning off the isos tomorrow to see if I can get a before and after test before I change the valve. I'll come back here to let you know how I get on.

 

[Daveydub]

Sounds like you have found it. I usually run shower till hot side of the valve is hot.
Then turn off shower.
Hot side will now go cold to the touch.

 

[sparer]

So, it was the bar valve that was the problem. I isolated it and the overflow stopped running (after about 3 hours!). I turned the isolators on again and the overflow started running again, isolated, and it stopped. Thanks to you all for assistance with this.