Swing valve or check vale and location

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In my mother-in-laws house she has a problem where the stored hot water tank is overflowing. The ball cock has been adjusted several times and finally a plumber has diagnosed the fault to the thermostatic bath mixer. He says I need to fit a non return valve to preferably the hot side as the higher cold pressure is backfilling the hot.

This does make sense to me as it's stored hot water but mains cold. The problem occurs even when the taps are switched off.

Can I confirm I need to fit a swing valve rather than a check valve as it's gravity hot water (stored only on the 1st floor)? Also where can I fit the valve? Presumably the best place is by the tap causing the problem but this involves ripping the bathroom apart. Can it be fitted elsewhere in the hot supply line, for example nearer to the tank? I understand if a swing valve the orientation is important.

Finally, the flow of hot water through this particular thermostatic mixer tap has always been very poor (it was good prior with separate taps), could this be related? I can't remember what pressure the taps were rated at but I'm sure they were suitable for low pressure.
 
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You need a single check valve in the pipe that feeds the tap and nothing else.

The clacker type swing valve would not be suitable.
 
you might also throw away the mixer and go back to separate taps; or if more convenient you could run a new cold water supply pipe from the loft tank to the bathroom.

If you fit a check valve, just take off the bath panel and put it on the HW pipe under the bath mixer. No need to dismantle the bathroom. You will still have problems with hot flow and mixing as the pressures at the tap are unbalanced

Whoever fitted a mixer tap on unbalanced supplies should have known better.
 
It was me that fitted it, and I'm not a plumber, so I should know better, but I don't! It was fine (but slow) however until she had a new boiler and tank fitted.

There is a vanity sink up against the bath which would need to be removed to gain access to the taps, that's why I asked if the NRV could be fitted elsewhere. I'll have a look and see if I can trace the pipe back to somewhere else more convenient.

Is there any type of mixer tap that can be fitted to unbalanced systems? She does tend to use the hand held shower quite a lot so wouldn't be so happy with separate taps.
 
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Hand held shower taps should have check valves on the hot and cold.

You you can buy BS kite-marked taps that mix in the spout and not the body.

Think they CE marked now.
 
It sounds like a pressure equalisation valve might be helpful in this situation, do I still need the NRV or are they inbuilt into the PEV?
 
are you sure you wouldn't rather run a cold supply pipe from the cold tank?
 
Defintely not, that would involve removing the vanity unit & sink and running a feed through three walls or two outside, which would be more cost and a lot more time.

Do the PEV include a non return system or do I need to fit a separate one. I don't want to restrict the hot flow any more than necessary.
 
It sounds like a pressure equalisation valve might be helpful in this situation, do I still need the NRV or are they inbuilt into the PEV?

Would be ideal and have non return built in
 
Excellent, thanks, just the answer I was looking for. I know the best solution is to run a new pipe to the tank but this is a retro fit not a new install so circumstances are different.

Thanks.
 

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