Shower, check valve. Confused

[richardrich79]

Having read most threads on the subject I now need help.
Walk in shower room. no chance of fixed head shower or additional hose shower 'siphoning' anything. Do I need to add doublecheck on cold water (mains) supply.
The instructions supplied don't say and I cannot find anything from Welsh Water on the subject.
All replies very gratefully appreciated.

 

[Charnwood]

Water mixes in - believe it or not - the shower mixing valve.
There is a risk of hot water entering the cold mains in the event of the mains back-syphoning.

 

[richardrich79]

I know there is a slight chance of the siphon in the valve and riser & my natural inclination is to fit the valve, my neighbour has redone his property in plastic and recons he was advised that 'the reg's' say that you only need one after the stopcock!
I was going to fit one at each outlet along with full bore isolators but having inspect the current set-up there isn't one there unless there is provision in the box, it's electric.
I'm confused

 

[Madrab]

As far as the water regs are concerned as long as you can avoid contaminating the mains water by whatever means necessary you then comply.
That can be by an air gap in the case of pillar taps/cisterns or a single check valve after the mains stop cock if you have mixers on the mains supply. Hot water is classed as Cat2 water so a single check valve is sufficient.
Your mixer shower may have built in backflow protection but any mixer taps that mix the water in the body of the tap will require CAT2 backpressure/backflow protection.

 

[neiltheplumber]

The shower cartridge or body will probably have an inbuilt check valve to prevent a crossover and back syphonage!

 

[xr4x4]

The cold is mains... What about the hot?

 

[Charnwood]

The cold is mains... What about the hot?

Err, I made an assumption there. The OP has not specified.