Hello and help to any fellow plumbers out there. I hoping that you may see someting that I've missed?

Just finished installing a complete bathroom. Customer is very happy with end result. However, The Bristain artisan bar shower (thermostatic) is only, at best, giving out luke warm water. The system is off a Combi (Ideal mini) The shower can accept between .5 to 5 bar. All other outlets give our hot water. (Allbeit the bath hot is a bit of a dribble)

The static pressure off the hot and cold from the basin (which is next to the shower) both read 2.25 bar.
The shower is piped the right way round. The body of the shower and left union nut does get hot.
When I run the cold bath tap, it does steal some cold from the shower and therefore allows some hot through.

I've ordered a new thermostat cartridge, but I've got this horrible feeling that even after changing it, It'll still be a luke warm shower. I have no obvious pipework to get on to to install a PRV. but in all honesty, it shouldn't require it, given the 2.25 bar and fed from a combi. Even Bristain say the shower can handle 5:1 ratio.

Any thoughts??

Have you done this??

6.1 The maximum temperature can be adjusted to suit site conditions or user
preference. To adjust this, follow this procedure:
6.2 Position the temperature control handle to the maximum temperature point and
turn on the flow handle control handle letting the water run long enough to ensure that
the hot water supply is at its maximum temperature.
6.3 The shower has been factory set to 38oC at the first stop position with balanced
supply pressures of 0.5 Bar.
6.4 Whilst the water is flowing remove the temperature control handle (15), by
removing the head cap (17) and unscrew the head screw (16).
6.5 Turn the cartridge spindle (a) until the required maximum temperature is achieved
(the spindle many need to be reposition to allow the head to line backup with the stop
ring (14) on the shower), anti-clockwise to increase the temperature and clockwise to
reduce it.
6.6 Important: Refit the handle so that the stop pin in the handle (15) fits inside the rim
of the nylon stop ring (14).
6.7 Push the handle back on and turn clockwise.
6.8 Turn off the flow at the flow control handle.

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Don't like the sound of the bath taps is a dribble.

Blocked or damaged pipe come to mind straight away.

What size have you run the hot for the bathroom.

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Thanks Razor... Yep forgot to mention that I re-calibrated the temperature handle and stop.

Thanks The Scruff....
I have come off existing 22mm which runs under the floor, first pass the shower. rises up in 15mm (used to be for the old basin but now the shower)

then on to w/c ( rises in 15mm as before)

then on to basin ( again rises in 15mm)

and finally terminates at bath still in 22mm .
I say a dribble.. it's a bit more than this, but I certainly wouldn't like to run a hot bath with it. A little disappointing shall we say.

You should get 10 -12Ltrs/min depending which mini it is.

So you can measure the flow rate at the bath, for starters.

I assume you haven't connected the hot to the wc.

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I will check the flow rate this week when I return to put in the replacement thermostatic cartridge.

I'm certain the w/c is on the cold but I will double check during my visit.

Appreciate all your help. Will report back with my findings.....God I hope it's the the cartridge.

Night night.

I wouldn't bother with the cartridge, until you sort the flow rate issue out.

Reason being if your not getting a flow into the bathroom/shower then you won't get a flow out.

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Evening Chaps

Thanks again for all your input and advice.
Today I went back to the job and replaced the cartridge with a new one from Bristain.
I was totally gob-smacked...... Hot water!! I was getting ready to go and get my flow cup and possibly a PRV but voila!
I still appreciate your help. Sometimes you can forget the most silliest of things and overlook them. So running it past the forum was a big plus. Drinks on me.

Regards PP.

Yes but has it improved the bath flow.

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No, the bath flow is still poor but the customer advised me that it was always a slowerer flow than the cold and it has always been a slow process to fill her bath (I should have enquired before I started the whole job! )
Just for info. The cold comes in on blue 20mm; stopcock to 15mm then tees off to boiler.
Hot out of boiler in kitchen - 15mm; rises in 15mm; tees off in 22mm left to barthroom, right to old H/W cylinder (thats now gone due to combi) capped off where - i dont know.
22mm runs under bathroom floor 1st tee up in 15mm to shower; 2nd tee up in 15mm to basin; terminating in 22mm in Bath. I only needed to adapt the last 2m in Hep20 so I know there are no blockages from my work.
(ps I'm not a lover of plastic - much prefer copper but had little choice due to flooring)
I never got the chance to measure the flow but I'm curios and the next time I'm there (to fit a new kitchen tap) I will unleash the cup. I've a funny feeling that the problem lies with the flow from the boiler, but will endevour to find out.
Thanks again Scruff i'll let you know my findings.