how to prevent cold water flowing back into the hot water pipe

[roobaru]

I have a single lever pull out kitchen faucet installed. The tap takes a hot and cold water connection, the cold is from the mains so is at a higher pressure. The hot is from the system boiler so is at a lower pressure. It seems to me that when I open the tap, the cold water is forcing its way into the hot water pipe due to the pressure difference. Is there anything that can be done to prevent the reverse flow?

 

[Ben-gee]

Yes, fit a non-return valve in the hot supply pipework as near to the tap as you can.

 

[Ric2013]

Better still, fit a tap designed for unbalanced pressures or fit a pressure reducing or equalising valve on the cold.

 

[roobaru]

Yes, fit a non-return valve in the hot supply pipework as near to the tap as you can.

Thanks Ben

 

[roobaru]

Better still, fit a tap designed for unbalanced pressures or fit a pressure reducing or equalising valve on the cold.

will follow this when I buy the next tap.

 

[Ric2013]

The pressure reducing or equalising valve on the cold, though, you could do now, with the existing tap. It would limit your pressure, but you'd have better mixing from your tap. Depends, though, whether successful mixing is more or less important than a good jet from your cold and only you can know how you tend to use your tap.

 

[roobaru]

Thanks Ben

The pressure reducing or equalising valve on the cold, though, you could do now, with the existing tap. It would limit your pressure, but you'd have better mixing from your tap. Depends, though, whether successful mixing is more or less important than a good jet from your cold and only you can know how you tend to use your tap.

Thanks for input Ric, so mixing is definitely important but at the same time, I do plan to replace the current system boiler with a mega flow system in the near future which hopefully should take care of the pressure issue. So which one would be a better option, a pressure reducing valve on the cold or a single check non return valve on the hot or should I go for both?

 

[Ben-gee]

Non return is cheaper fix and will sort out your problem until unvented cylinder update in near future - which is a very good idea, you’ll be pleased with it!

 

[Ric2013]

Thanks for input Ric, so mixing is definitely important but at the same time, I do plan to replace the current system boiler with a mega flow system in the near future which hopefully should take care of the pressure issue. So which one would be a better option, a pressure reducing valve on the cold or a single check non return valve on the hot or should I go for both?

If you fit a PRV, you don't need a check valve.

As Ben-Gee has suggested a check valve less than £5 in UK, while a PRV can cost around £30. So depends how temporary this has to be.

If you go for the check valve, you need the check valve on the higher pressure side, so I would put it on the cold in your case - not the hot!

 

[roobaru]

If you fit a PRV, you don't need a check valve.

As Ben-Gee has suggested a check valve less than £5 in UK, while a PRV can cost around £30. So depends how temporary this has to be.

If you go for the check valve, you need the check valve on the higher pressure side, so I would put it on the cold in your case - not the hot!

The current plan is to have this sustain for the next 3-5 months until I sort out the build plans. I am a bit confused, why would the NRV be on the cold pipe, shouldn't it be on the hot water pipe to prevent the cold water from flowing back in?

 

[Ben-gee]

Yes, put it on the hot.

 

[Ric2013]

Apologies for paragraph 3 in post #9 which is completely incorrect. As Ben-Gee has correctly noted, the NRV should be on the hot not the cold!

Do bear in mind the classic spring-loaded NRV will have a detrimental effect on the flow/pressure of the hot water.

 

[Johnyc86]

I have a single lever pull out kitchen faucet installed. The tap takes a hot and cold water connection, the cold is from the mains so is at a higher pressure. The hot is from the system boiler so is at a lower pressure. It seems to me that when I open the tap, the cold water is forcing its way into the hot water pipe due to the pressure difference. Is there anything that can be done to prevent the reverse flow?

Put a pressure reducing valve on cold main before it goes to tap

 

[roobaru]

Apologies for paragraph 3 in post #9 which is completely incorrect. As Ben-Gee has correctly noted, the NRV should be on the hot not the cold!

Do bear in mind the classic spring-loaded NRV will have a detrimental effect on the flow/pressure of the hot water.

No worries Ric, Thanks to you and Ben for guiding me. Are there any alternatives to the classic spring-loaded NRV's?

 

[Ric2013]

Yes. You can get swing valves. Technically they don't meet the legal criteria for backflow protection but in this case you are making an existing system more compliant than it previously was, so I wouldn't over-worry about that.

Having said that, swing valves are not as cheap as the spring-loaded ones and the difference between a NRV and a PRV is now less.

 

[Ben-gee]

Just get a spring one, it’ll be fine.

 

[roobaru]

Just get a spring one, it’ll be fine.

ok, thanks

 

[Ric2013]

Just get a spring one, it’ll be fine.

Unless he's only got 1m head?

 

[TimboTwo]

He won't get any hot unless fully over to hot side, as the pressure from the cold will keep the nrv shut.

 

[Ben-gee]

That’s liveable with if it proves to be the case, however I have done this often and find a warm blend is available, obviously only add in a bit of cold.
The idea is to stop the cold back filling the cylinder and ultimately the CWS , I’ve seen the aftermath of this and it’s not pretty.
The OP is also updating system soon.