Non-return valve on thermostatic shower

[igaquo1]

Hi there

Do non-return valves on a thermostatic shower reduce the water pressure coming out? (using a combi boiler).

thanks
Jeremy

 

[leakydave]

It depends on your water pressure but I doubt they will make a noticable difference.

 

[ianmcd]

No they shouldnt do and its a good idea to have them installed to stop back feed from cold supplies which is a common problem with thermostatic showers with combis

 

[igaquo1]

What do you mean by "feed back from cold supplies" in practice?

 

[ianmcd]

well if you think about how a combi shower works the cold water comes direct from the mains where the hot has to go through the combi boiler so will encounter plate heat exchanger , flow restrictor etc so cold will in most cases be at a higher pressure/flow rate to the hot and if the mixer valve is not 100% then you get cold blending back into the hot supply

 

[igaquo1]

Well i've just bought a water pressure gauge. The water pressure coming out of the shower is disappointing following installation of a combi system, but the hot water coming out of the kitchen tap is ok. Installed a Worcester 34CDi. The plumber told me the cold water pressure was about 3 bar.

 

[ianmcd]

I think you are confusing water pressure with flow rate, the amount that comes out of your shower head is flow rate, to be honest water pressure doesnt really mean much its flow rate you are interested in, you measure flow rate with a cup called a weir guage, water pressure is the pressure that the water in your pipe will reach with nothing flowing and to be honest means diddly squat to anyone except a system designer and what pipe fittings to specify to withstand such pressure

 

[TicklyT]

You can get a good idea of the flow rate you are getting with a bucket and a watch.

Just time how long it takes to fill a bucket of known capacity - eg if it takes 30 seconds to fill a 10 litre bucket, the outlet is delivering 20 litres per minute.

Your boiler's capacity to heat water may limit the hot flow rate you can achieve with a reasonable hot water temperature.

 

[igaquo1]

Well here are my stats:

At garden tap:
Water pressure: 2.5bar
Flow rate: 20L per min

In bathroom:
Thermostatic shower valve (38C): 13.5L per min
Hot bath tap: 13L per min

DHW temp: 48C
Cold water temp: 10C

Boiler Worcester 34CDi

So do the bathroom flow rates appear reasonable? Because frankly I am a little disappointed!

 

[igaquo1]

So do these bathroom flow rates seem ok? The plumber suggested removing the non-return valve to improve the flow. But based on the manufacturers handbook, it doesn't appear I can get much more DHW flow.