Another mixer shower question

[rachstella]

I intend to fit a simple bar type mixer shower in my bathroom. I have a sime friendly combi 80t which just runs a bath and 2 sinks. I dont want to use the bath just a shower. I have found behind my bath, 22mm and 15mm supplies both capped off. Which i presume is for a shower.

My question is do i need to fit isolating valves on both hot and cold or a combined check valve to prevent backflow? Can i run the supplies in 15mm to the mixer?

Thanks.

 

[Fluffster]

Isolating valves would be handy for future servicing etc but do reduce the flow rate unless you go for full bore valves.
Using 15 mm pipe to feed is fine.
You may find the mixer unit may have a non return valve built in, these seriously restrict flow so make sure you do not duplicate although you are running hot and cold mains fed they should be close to equal.
Pete