Where do I need NRVs or check valves in a combi setup?

[Laggy]

Hi

In terms of both regs and from a plumbers’ perspective, is there anywhere I should add a non return valve or check / double check valve in a combi setup?

I’ve looked into it a bit, and I see the technical difference between a NRV and single / double check valve but I’m still not sure where I should put any?

I assume one goes between the mains stopcock and the appliances, but not sure which, and also if I should add any others anywhere else for the mains supply or for the CH flow/return circuit?

Thanks for any advice.

 

[ianmcd]

your filling loop in a combi should already have this incorporated

 

[Madrab]

The other reason you may fit one is if the boiler cycles on when cold water is drawn, then you would put a single check valve on the cold feed.

The only other place that a double check valve should really be used (as per water regs) is at the mains entry point after the mains stop tap but that can effect mains pressure, if the mains pressure is on the low side to start with.

 

[vulcancontinental]

I'd just add if you have a water meter it incorporates a NRV and anyway and it's advisable I believe to install a small expansion vessel on the cold main entering the combination boiler if you add an NRV.

 

[Laggy]

your filling loop in a combi should already have this incorporated

Yes done this, it’s a Tesla remote one with gauge, and double check valve.. thanks for checking

The other reason you may fit one is if the boiler cycles on when cold water is drawn, then you would put a single check valve on the cold feed.

The only other place that a double check valve should really be used (as per water regs) is at the mains entry point after the mains stop tap but that can effect mains pressure, if the mains pressure is on the low side to start with.

Is the first one you mention because the “pull” of the cold demand from elsewhere tricks the boiler switch to think there’s a demand for hot as the diaphragm in the switch moves? Just testing my newbie knowledge here.

The second location is what I thought I needed, but I’m reluctant to restrict my pressure in this way, I was going to put a pressure reducing valve here and set it to what the boiler wants. Thanks very much for your advice.

I'd just add if you have a water meter it incorporates a NRV and anyway and it's advisable I believe to install a small expansion vessel on the cold main entering the combination boiler if you add an NRV.

I do have a water meter, and is that what I am calling a shock arrestor? As I was going to include one, just checking and thanks a lot

 

[vulcancontinental]

No, you need a shock arrestor or expansion vessel because a NRV prevents expansion back into the municipal mains. The shock or increase in pressure with nowhere for absorbing pressure could start a flow turbine or if expansion of pre heated water is great enough damage components or O rings.

 

[Laggy]

No, you need a shock arrestor or expansion vessel because a NRV prevents expansion back into the municipal mains. The shock or increase in pressure with nowhere for absorbing pressure could start a flow turbine or if expansion of pre heated water is great enough damage components or O rings.

Cheers mate, I understand all of that, thanks, except for the word ‘no’. What is that bit in response to? Me saying I’m including a shock arrestor is that good enough? As in, no it’s not good enough? Cheers

 

[vulcancontinental]

"I do have a water meter, and is that what I am calling a shock arrestor?"

No, the meter is not the shock arrestor. That's what I read but I see that's not what you meant.

 

[Madrab]

Is the first one you mention because the “pull” of the cold demand from elsewhere tricks the boiler switch to think there’s a demand for hot as the diaphragm in the switch moves? Just testing my newbie knowledge here.

yup

 

[Laggy]

"I do have a water meter, and is that what I am calling a shock arrestor?"

No, the meter is not the shock arrestor. That's what I read but I see that's not what you meant.

Sorry mate sometimes I write a little “off”.

So going back to your advice, if I have a water meter, and I use a shock arrestor, then I’m all good? Cheers

 

[Laggy]

yup

Yay I got something right

 

[vulcancontinental]

Sorry mate sometimes I write a little “off”.

So going back to your advice, if I have a water meter, and I use a shock arrestor, then I’m all good? Cheers

Yes