Shower flow pressure query

BobbyJoe · Mar 3, 2022

Hi everyone,

I have a question regarding the flow and temperature on a thermostatic mixer shower. The water set from the combi boiler is hot in the kitchen, the bath hot water tap is quite warm and when I reduce the flow by turning the tap half way the water gets hotter.

My shower has been warm so I decided to reduce the flow to see what happens ( I always have the flow fully turned) and the water became hotter and I still have good enough water pressure. My question is, why does the water get hotter when the water flow is reduced and is it okay to keep on using the shower with half flow water pressure rather than full flow?

Any information would be appreciated thanks.

Shower bar looks similar to this:

Cruze Round Top Outlet Thermostatic Bar Shower Valve | Victorian Plumbing UK

SHOP the Cruze Round Top Outlet Thermostatic Bar Shower Valve at Victorian Plumbing UK

www.victorianplumbing.co.uk

John.g · Mar 3, 2022

No problem with reducing flow rates.
The boiler output and the mains cold water temperature determines the hot water temperature, If you have a 30kw combi and assuming a cold mains temp of 7C then the hot tap will flow 15.4LPM at 35C, 11.3LPM at 45C, 8.1LPM at 60C, the max combi temperature allowed is I think 60C so you can further reduce the flow to at least as low as 3LPM at 60C, the boiler will reduce its output to maintain this temperature.
Your shower is similar, you are throttling the flowrate to achieve the same as above, only difference is that the thermostatic mixer probably only allows a max temp of say 48C, in this case the max shower flow rate will have to be reduced to 10.5 LPM, you can also keep reducing this flow rate right down as the thermostatic mixer will then control the temperature and the boiler will reduce its output.