Fitting non return valve to thermostatic mixer bath taps

[Jumbo Jim]

View attachment 281943

Hi,
It was suggested to me that I should fit non return valve(s) to the hot and cold pipes supplying the mixer thermostatic taps on my bath to prevent backflow.

I am thinking of getting a pair of 22mm flexi hoses and attaching 22mm non return valves and then fitting these between the taps and existing flexi hoses.

Does that make sense ?
Any advice in terms of do's and don'ts ?
Is there any need to fit a double NRV as opposed to a single ?

PA - Hot water is fed from combi boiler.

TIA - JJ

 

[Madrab]

If hot and cold water is from the same mains then no real need for a NRV, as the supplies are balanced.

 

[Jumbo Jim]

It was a plumber who'd repaired the combi boiler (in my absence) who said the cold water passes through the tap and backfeeds.
He said he'd discovered this when he'd isolated the boiler supply and water was still under pressure.

He recommended fitting nrv to pipework so I'm just trying to avoid further costs getting him back out if it's a straightforward fix.

 

[Madrab]

Understand why he mentions that but that's down to the fact that either a faulty valve or cartridge that's allowing crossflow from cold to hot.

Under normal circumstances it wouldn't make any difference as the mains and the hot water are both at the same pressure so there wouldn't be any crossflow when both are on and if the mains was isolated for servicing, again there wouldn't be an issue. It would only be noticed when the cold inlet to the boiler was isolated with the mains still on, then a faulty valve could send cold water down the hot side and backflow into the boiler.

Rather than suggesting fitting NRV's I'd probably suggest finding the faulty valve/cartridge and fixing that.

 

[Madrab]

BTW ... NRV's are non return valves these are different from check valves which are either single or double and usually verifiable and provide a more specific backflow protection.

 

[Jumbo Jim]

Cheers - the taps have been there about 10 years so will have to check out make/model etc to see if replacement parts are available for it.

 

[Madrab]

A little test could be to turn off the cold inlet to the boiler and then run the mixer tap on hot, if it give cold water then that will prove if the cartridge is crossflowing from cold to hot.