Check Valves on Mixer taps - on hot and cold supply?

[SkipFeeney]

Hi,

I have got an open vented system with a hot water water cylinder supplying the hot water to a mixer tap and the cold being supplied by the mains.

I have just realised that i need to install a check valve to prevent the hot water from going down the mains. Do i have to install a check valve on the hot water side too? What are the risks of cold water going down the hot supply?

Thanks

 

[Madrab]

Other way about, the cold pressure will restrict the hot water flow. Strictly speaking all single mixers should have NRV's fitted to avoid backflow. Are you experiencing any problems with the tap?
This is just about restricting flow rather than contaminating the mains though. You should always try to use a balanced H&C supply or taps suited to a mixed suppy (dual flow).

A check valve should be used just after the mains stop tap to protect the shared main from backflow but invariably it isn't.

 

[SkipFeeney]

I have only just set everything up but when i run the cold tap i can feel the hot pipe vibrating, I have an awful feeling that the cold water could be displacing the hot water from inside the tap and going down the pipe. I guess what i need to do is run the hot water so the pipe work is hot and then the cold water and see if the hot water pipework suddenly becomes cold? Is that a good test?

Good point actually - so I could fit a check valve straight after the stop cock - will that remove the need for adding one to every mixer tap on the cold side?

 

[Madrab]

It should only happen when the hot is opened when the cold is running, when the hot is off the hot water valve is closed so it won't travel down the pipe.

so I could fit a check valve straight after the stop cock - will that remove the need for adding one to every mixer tap on the cold side?

Depends what you are trying to achieve, if you wish to avoid backflow contamination of the cold mains then yes fit one, it won't stop the cold water restricting the hot water in a single flow mixer tap with an unbalanced supply, when both taps are opened