combi boiler hot water pressure

22 Feb 2013
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United Kingdom
I recently changed my vented system to a combi boiler worcester greenstar 38cdi.
Most of my taps have good hot water pressure but some do not ?
Mainly the bath filler and the shower although both not from the same supply

Ive been looking for a common link to why but unable to find anything.
The only thing which ive noticed but im unable to investigate further without taking up floor boards is that where the old immersion tank was the pipe is 22mm and the hot water leaving the boiler is 15mm.

All hot water taps are connected by 15mm so therefore somewhere under my floor boards the hot water supply goes from 15mm to 22mm then back to 15mm before the tap.
Would this have a reducing effect to the hot water pressure ?

Im now wondering if the hot taps with good pressure are 15mm straight through to the tap without the step up to 22mm and back down to 15mm in size.
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I would forget about pressure and measure flow rates from each outlet, and compare it with the data in the manufacturers instructions and see how each one compares.
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Have you, or anybody, checked the 'pressure' AND flow rate or do they just look less than the other taps?

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