Non return valve- Hot water bath?!

[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

 

[ShaunCorbs]

That’s what it’s designed for so why not ?

 

[Welder]

That’s what it’s designed for so why not ?

Do you mean the pressure equ valve?

 

[ShaunCorbs]

Do you mean the pressure equ valve?

Yes

 

[Welder]

Yes

Now you've done it Shaun

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

 

[Deleted member 84317]

Now you've done it Shaun

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

Is it worth closing the isolation valve on the cold somewhat, to see if it helps my issue?

 

[Welder]

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.

 

[Riley]

You keep asking the same question the answer doesn’t change

 

[Warmiger]

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

 

[Darren Jackson]

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

 

[Riley]

And you’ll never get the pressure balanced