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Unvented cylinder/shower valve

View the thread, titled "Unvented cylinder/shower valve" which is posted in Showers and Wetrooms Advice on UK Plumbers Forums.

S

Steveo111

Hi All
I had an unvented cylinder fitted about 6 years ago. It only supplies hot water to my shower. I was hoping for a much better flow rate from the shower but it seemed no different from the original combi boiler hot feed. There is (unusually) a lever that lets me select the combi or the unvented to supply the shower feed and, because the unvented cylinder had no noticeable effect, the unvented cylinder rapidly fell into disuse. Disappointing.
My brother recently had an unvented cylinder fitted and his shower is now like wrestling an anaconda - marvellous! Lots of gushing hot water! So I have fallen to wondering about mine again.
I have 3 bar mains pressure and standard water pipes. The garden tap delivers about 11 litres per minute. Assuming the unvented cylinder is not faulty, is it most likely the shower valve that is reducing the flow to the shower head?
The valve is an exposed Bristan 'Sonique' (with flow reducers removed). My plumber (who is great with heating) just told me to choose a shower valve (so I did!) and I think that may be the problem.
Unfortunately the hot and cold shower feeds are set only 150mm apart and it seems only the Bristan will fit, so to change the valve the tiles will have to come off and the pipes adjusted etc., so it is a bit of a job.
I'd very much appreciate any comment on whether the valve is likely the problem (maybe a way to test it?) and what might be a suitable replacement exposed thermostatic valve (mid-range for cost and ideally with a lever) before I embarrass myself asking my plumber to swap the existing valve out(!)
Best regards.
Steve
 
150 centres is standard, probably 95% of shower valves .

If you only have 11 lpm incoming mains then that is all you will get out of your shower when fed by either a combi or an unvented cylinder.
Tbh it’s unusual to install an unvented on that poor a mains flow, most plumbers would advise against it below 20 lpm.

You either need to upgrade the mains supply, or fit accumulator and possibly pump set to see any improvement from your mains fed system.

Or go back to gravity stored water and pump from there.
 

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