installing bath and shower mixer

22 Jun 2012
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United Kingdom
Just looking for a bit of advice please.
Planning to fit a new P shaped shower bath in a slightly different location in existing bathroom. I have a Worcester Junior greenstar 24i combi boiler in the airing cupboard in the same bathroom. I reckon the hot pipe run straight to bath from boiler is about 2.5metres. The cold feed from outside is 15mm throughout the house. the hot feed from the boiler is 22mm to the current bath taps reducing to 15mm going to basin - then downstairs to kitchen directly below. I want a mixer tap on the bath with a portable shower head attached like this one , and then a separate thermostatic shower valve halfway up the shower wall pipes hidden behind the tiled wall to the top shower head. Ive been told that the boiler should be fine to do this

can I reduce the 22 mm pipe out of the boiler straight down to 15mm and route it to the bath taps (increasing to 22mm if required), tee to the shower valve then tee to the basin then tee downstairs all in 15mm? Will this give me the best water pressure? are all bath taps 22mm?

Or should I just leave it at 22mm to bath taps reducing tee down to 15mm for the rest? this is what it does now - only I have an electric shower at the moment which I want to get rid of.

thanks for any help
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Just leave it as is for minimum upset. Get a thermostatic bath shower mixer to minimise effects of other hot water draw offs. This will prevent hot and cold showering. Hope this helps.
Your boiler can only produce a certain litres per min, roughly 11 per minute, as u see from your boiler hot outlet it 15mm as this is suitable. Whatever way you pipe it if someone else opens a hot tap while your having a shower the water flow rate will drop. Presure is reduced when it enters the boiler as it can only heat what the manufactures instructions state. So i would leave it as it is and just tee off under bath gor your shower. Hope this makes sense ;)
thanks for replies. I will just leave as it is then
thinking of buying this from ebay

should I fit a double check valve to the hot on one of these?

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I doubt you'd be able to run that from a combi, and indeed it says in the listing that it requires an unvented cylinder.
It will work fine from a combi, minimum pressure 1 bar it says. Also says for use with combi boiler ;) i fit these all the time, great pressure! It wouldnt do any harm fitting a check valve incase the shower becomes faulty and passes.
It wouldnt do any harm fitting a check valve incase the shower becomes faulty and passes.

stick the double check valves on both the hot and the cold?

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