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Deleted member 84317

Hi

(System is header tank in loft, indirect hot water tank)

After the hot water isolation valve under my bath, there is a non return valve between the isolation valve and the hot water tap.

When I switch the hot water (mixer tap) on in the bath nothing happens until I flick the SINK mixer tap on and off and then the hot water runs in the bath (the non return valve sticks closed, till you mess with the sink mixer tap).

I have tried without a non return valve in the line but then water comes out of the overflow from the header tank in the loft, to the outside, so I have put a new non return valve back in.

Now the sink 'trick' doesn't work any more N.R Valve must me stuck closed and won't release. Clearly the N.R valve shouldn't be there.

Any ideas anyone?

Regards
Adam
 
You’ve installed the nrv the correct way ?
 
Yes if the cold is mains fed
 
Yes it needs to be there, you've found out what happens when it's not there.

There probably isn't sufficient pressure on the hot side to lift the spring in the NRV.
 
correct way
 
Oh Have you any suggestions for my problem?
Seperate hot and cold taps or a mixer that only allows the mix after the valves, the normal advice for your type of tap and water system would be to fit an NRV, if the pressure is too low to operate the NRV then new taps - unless you want to get a pump installed, but the expense and future maintenance is more costly/problematic than just getting new taps.
 
Sounds like you need new mixer tap, the cartridge has bust and it’s sending cold water up the hot pipe back filling the cylinder then up the expansion pipe, filling loft tank then out of the over flow.
Some idiot has tried a cheap fix by fitting a non return on the hot but the, pressure on the cold is greater and keeping it shut until you open the other tap.

New taps and bin the nrv ;)


Seen it loads
 
The correct thing to do would be to equalise the pressure by running a tank fed cold to your bath.

You could try a low pressure non return valve.
 
Well depends if the taps at fault can you remove the hot side cartridge

This is the tap (photo’s). I can remove it, what do you think?

image.jpg


image.jpg
 
You actually do need NRV's on both the hot and cold pipes as per water regs, one to stop the cold forcing its way up the hot water pipes and filling the header tank up and the other on the cold feed pipe for backflow prevention and possible cross contamination of the potable water. If you are having problems then fit a pressure reducing valve on the cold feed pipe to the tap in question to balance the feeds.
 
You actually do need NRV's on both the hot and cold pipes as per water regs, one to stop the cold forcing its way up the hot water pipes and filling the header tank up and the other on the cold feed pipe for backflow prevention and possible cross contamination of the potable water. If you are having problems then fit a pressure reducing valve on the cold feed pipe to the tap in question to balance the feeds.

Water regs would say you would need one on the cold feed as it cat 2? I think.
 
The problem is cheap taps can't cope with the pressure difference so as someone else has said if you do change the taps you need one that mixes outside of the spout.

Otherwise re pipe your cold feed and remove the non return valve.
 
Wouldn’t say that tap was good for low pressure installs / unbalanced
 
Would reducing the cold pressure by using the isolater valve be worth a go/experiment?

From my experience no. You either re pipe or change the tap. You can try fitting pressure reducing valves, using an isolator that will eventually start leaking as they don't seem to like being left inbetween, you can try a low pressure non return valve but eventually you will end up replacing the tap or re piping it.
 
Bes sell a banalncing valve for mains to gravity hot water

Water Pressure Equalising Valve - 16711 | BES.co.uk

That will not work for this Shaun. The max difference in pressure is too large.

That tap is actually not too bad for pressure. However, the only way to make it safe and not have the cold pressurising the hot supply is to swap the tap for two seperate, traditionally valved, taps.
NO modern (1/4 turn) type bath tap will work with pressure this low.
Some kitchen taps keep the water seperated until the spout end (so you'd not get the back pressure) but the hot flow rate with still be appalling.

Sorry. It's bite the bullet time.
 
That’s what it’s designed for so why not ?
 

Now you've done it Shaun :rolleyes:;)

PEVs work within a range. That is, they can equalise pressure so long as one is not too far away from the other. The one you show, the one most commonly sold in the UK, works on a max 10:1 ratio.

If one side is 0.2bar & the other 2.1bar then it simply does not work. It cannot adjust enough. So, with typical mains being 3 bar, and a good low pressure system being 0.25 it cannot work.

However... What I've done in the past, with a system that was 0.25 on the hot, was install a pressure reducing valve locally on the cold supply and adjust it right down to 2 bar. It just about worked and, to be fair, has done well for about 6 or 7 years.

The truth of the 10:1 ratio is that it depends on manufacturing tolerances. This means many just can't get down that far. PEVs are much better & reliable if they are used so there is more like a 5:1 ratio.

Lastly, the diaphragm of a PEV has a small hole in it. It's part of their design. ALL PEVS should have NRVs fitted in both lines but of course that further restricts flow on a low pressure hot system.

Where they are delib left out you WILL find back filling of the hot water tank and, if left unused long enough, symptoms of a perforated cylinder coil (albeit in the wrong cistern) in that the loft tank eventually overflows. Of course that completely negates their WRAS approval too if left out.

HTH and yes I am 'offically' a sad fooker :cool::D
 
Now you've done it Shaun :rolleyes:;)

PEVs work within a range. That is, they can equalise pressure so long as one is not too far away from the other. The one you show, the one most commonly sold in the UK, works on a max 10:1 ratio.

If one side is 0.2bar & the other 2.1bar then it simply does not work. It cannot adjust enough. So, with typical mains being 3 bar, and a good low pressure system being 0.25 it cannot work.

However... What I've done in the past, with a system that was 0.25 on the hot, was install a pressure reducing valve locally on the cold supply and adjust it right down to 2 bar. It just about worked and, to be fair, has done well for about 6 or 7 years.

The truth of the 10:1 ratio is that it depends on manufacturing tolerances. This means many just can't get down that far. PEVs are much better & reliable if they are used so there is more like a 5:1 ratio.

Lastly, the diaphragm of a PEV has a small hole in it. It's part of their design. ALL PEVS should have NRVs fitted in both lines but of course that further restricts flow on a low pressure hot system.

Where they are delib left out you WILL find back filling of the hot water tank and, if left unused long enough, symptoms of a perforated cylinder coil (albeit in the wrong cistern) in that the loft tank eventually overflows. Of course that completely negates their WRAS approval too if left out.

HTH and yes I am 'offically' a sad fooker :cool::D
Is it worth closing the isolation valve on the cold somewhat, to see if it helps my issue?
 
Is it worth closing the isolation valve on the cold somewhat, to see if it helps my issue?

No. Closing a valve DOES NOT alter pressure. What that does is alter the flow rate (not as much can flow due to orifice restriction) so your problem would not change.
 
Hi

Just read this why not install a single impeller pump on the hot feed. You can get a pump fairly reasonable with a 5 year warranty. Most of these go for 10 years. You already have one cheque valve so one more installed on the cold to meet regs.
Good pressure on the hot and cold then. Less time on filling the bath up too.

Regards wayne
 
Hi

Just read this why not install a single impeller pump on the hot feed. You can get a pump fairly reasonable with a 5 year warranty. Most of these go for 10 years. You already have one cheque valve so one more installed on the cold to meet regs.
Good pressure on the hot and cold then. Less time on filling the bath up too.

Regards wayne

You could need to install a bigger header tank if you fit a pump. And will need double check valves not just single check nrv
 

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