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Mains Shower Unit - Help From A Plumber/Heating Engineer Please!

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moggie 939 | 13:03 Wed 12th Jun 2024 | Home & Garden
11 Answers

My shower works from my boiler hot water and until last week had a round control on wall with MIRA on it and two controls - main one was hot/cold by turning it and othere was a lever which adjusted flow. It has been fantastic for 10 yrs but started to leak so my landlord has replaced it with a different one - a Bristan which is a horizintal chrome bar with a central lever marked hot and cold. They took ages trying to set it up correctly and kept doing adjustments inside with an allen key or some such! It still is terrible.

There is no separate control for speed of flow and it is either cold or very hot! So how do I adjust the rate of flow as before as this seems very cheap.

I am thinking of getting my own plumber to replace it with a Mira as I had before. Also when turned it of it still drips sometimes through the shower head and I have to remove this and place on floor. Sometimes it drips a lot even when I have not used shower but have run taps somewhere in flat!

Any help most appreciated



Thanks so much




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Thanks Moggie.  You haven't given us the exact model number (I can't find one with a 'Q' in it.)Is this the one? so, then it's the right one for your system.  I guess it was the flow regulators that they were fiddling with (H&C).I read some reviews, and it seems to be quite an...
17:45 Wed 12th Jun 2024

Never seen one like this and Googling doesnt reveal anything resempling what you describe.  Do you know the model or can you post a link to which Bristain shower bar you have?

BTW, there is a world of difference between Bristain and Mira.  You get what you pay for usually with plumbing.

They've messed it up Moggie.  Out of the many, many shower valves I've installed, I've never had to fiddle with the shower valve to get it going. In fact, I can't even think of exactly what adjustments they could have made. Factory settings should be correct from the start.

They've either got the H & C the wrong way around...

Or: They've installed the wrong unit. There is a huge difference between the incoming pressure on a Combi system and a Gravity one (immersion tank in airing cupboard.)

You say 'boiler hot water'. That doesn't tell us which system you have I'm afraid.

Forgive me... just noticed you said 'mains unit', so I guess it's a Combi.

If they've fitted a 'low pressure' 'gravity' unit by mistake, that could be the problem.

Is it this in which case one end is flow rate and the other is temperature


Question Author

Hello Builder and everyone

I cannot find photo of m ine online but is like Prisms but only a lever in middle and both ends are blank. I have a photo but do not know how to send it to you!

I have a Vaillant Eco boiler. No it is not that one Fitser but similar with lever in middle showing H and C and blank ends


Question Author

Hello The Builder

Went into Bristain site and found it! Prism Exposed Single control PM2SQSHXVO C

Cannot believe price!! My one looks ***



Thanks Moggie.  You haven't given us the exact model number (I can't find one with a 'Q' in it.)

Is this the one?

If so, then it's the right one for your system.  I guess it was the flow regulators that they were fiddling with (H&C).

I read some reviews, and it seems to be quite an effort to operate.  People complain about it being difficult to get the exact temperature, and overall control is not terribly user friendly.

It really does seem to be the flow regulators that haven't been set up properly. I don't want to rub it in, but you don't get that with 'Mira'.

Nothing we can do from here I'm afraid, but their 'Customer Services' are apparently very good.

Give this a try.....

0330 0266 273

Question Author

Thanks for telling me all this and I understand what you say.

What I do not understand (sorry for being obtuse I am 84!) even if they get the temp correct how do I control the power of the water flow which was a separate control on the MIRA. There does not seem to be one at all on this model so am I stuck with no options to increase/decrease it?

Thanks again


Yes. As far as I can see, you have only one rotary control. You turn it up until it hits a 'stop'. In the Bristan, this is set to 42 degrees C. In other showers I've fitted, you can press the stop in and override it to a higher temperature. I can't find any info on this model to see if that can be done here.

There are no separate 'Temperature' and 'Flow' controls with this model. These are balanced  so that your selection on the single control valve will give the Temp. and a preset flow rate.

It's a perfectly good system BUT it does rely on the flow regulators being set up correctly, which obviously hasn't been done here. You really need someone who knows exactly how to do this otherwise you will get the erratic symptoms you have now.

Question Author

Thanks for this comprehensive reply The Builder. It is working ok now. The 'engineer' and I use that term losely! came back this morning having spoken to Bristan and he came with a new 'insert'  He opened the front and rerplaced this and then told me that I must turn the lever fully clockwise to 9 o'clock and back until is was correct temp. He tried it and it took a while to get temp correct by him using allan  key? and then checking temp of water coming out of head. Then the flow was too fierce which he seemed to adjust.

First shower was nowhere as good as my Mira! I will give it a while and if not I will pay for a proper plumber locally who like yourself has fitted loads!

Thanks again



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