Is there any Building Regulation that would prevent the use of a pull out nozzle kitchen tap,
when the new build has an unvented supply?

Is there any pull out kitchen tap that is WRAS approved? If not, is there any pull out kitchen tap that is unobjectionable under BR (with an unvented supply)?

 

Edited July 30, 20224 yr by WWilts

Never been asked and doubt they care. Don’t forget that the WRAS shower requirements only apply to bathroom waste water not kitchen sinks. 

Wow, I really hope your BCO ist that fussy.

 

We have a quooker flex and it's wonderful(ly expensive).

Assuming anyone can be that fussy a double value should satisfy any requirement. Being new build there should be a nrv on the meter, a check valve on incoming main and one on the combination valve to unvented cylinder. Again, if anyone cares. Generally speaking, replacement taps are not notifiable. Antibackflow and UK air gaps most satisfy the water company. 👍

Is a risk of back-flow the concern? Maybe put non-return valves on the feeds?

There is no requirement and no need to do backflow protection on a kitchen sink supply.
 

Furthermore, if the plumber has correctly installed the control group on the UVC and used the balanced cold for all outlets then the pressure differential that could cause this (ie the old hot cistern supply, cold mains supply) cannot occur. Also, feeding the WCs from before the control group means that a WC flush affects control group pressure equally so you don’t get the fluctuation in hot/cold balance. 
 

All of that above is industry good practice and should be done as a matter of course, yet I still see plumbers saying “that’s not how we’ve done it before….”

I'm not disagreeing, just interested in discussing the theory... I thought that the reason for a non return valve (eg on a garden tap that can be attached to a hose) or an a-type air gap (toilet cisterns) was to stop anything unpleasant being sucked back into the mains system if, for example, the fire brigade tapped into a hydrant up the road and caused reverse pressure?

Ok but you need to understand the classes of waste water - toilets / outside / shower/ bath  / basin / kitchen is pretty much the water regs treat domestic water with the controls required. You can add to it but a properly designed system doesn’t need it. 

46 minutes ago, Roundtuit said:

the fire brigade tapped into a hydrant up the road and caused reverse pressure?

Can’t happen - there are min 2 NRVs between the main and the house (meter and DCV on inlet). The issue is with low pressure hot being displaced by high pressure cold, and also fecal coliform entering the cold supply when flow stops. There is also a syphon element when a higher pressure outlet is opened and draws on a lower - again, proper design stops this.