Thermostatic Bath/Shower mixer and pipe sizes

30 Oct 2013
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Mid Glamorgan
United Kingdom
Hi all,

I've searched the forum but not seen an answer that will put my mind at rest fully. I'll try and give you as much info as possible and hopefully someone will be able to point me in the right direction.

I have just bought a thermostatic bath/shower mixer to replace the current taps on my bath. My hot water is supplied from a combi boiler in the bathroom via a 22mm pipe (I think it comes out of the boiler at 15mm and changes to 22mm which then feeds the hot bath tap via a 22mm tee off and continues on to the kitchen below, although I might be wrong about the size it comes out of the boiler, but I guess you guys will already know the answer to that :D ) and the cold is 15mm. Am I ok to cut the tee'd off 22mm hot water pipe that goes to the hot bath tap, and then use a 22mm to 3/4 flexible hose push fit fitting for the hot and a 15mm to 3/4 flexible hose push fit fitting for the cold. Or will I need to reduce the tee off from 22mm to 15mm and then use a 15mm to 3/4 flexible hose for the hot as well?

I hope that make sense, and my apologies if it's a bit of a stupid question.

Thanks in advance,

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You could yes but do remember that the flexible hoses have a reduced internal diameter. That being said I have 15mm pipes feeding a bar mixer shower without a reduction in flow so a 3/4 flexi ID shouldn't be much less than 15mm. Pressure will be similar given they are both 'mains' fed so balancing shouldn't be an issue.
Get ones with integral service valves if you don't have them already on the bath feed pipes
Thanks for the reply :D, so just to confirm, you are saying I don't need to reduce it down to 15mm and I can just use the push fit hoses?
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