Should I install A Pressure Reducing Valve?

[Steve1138]

Hi all

I’ve got an unvented hot water cylinder in my house with a 3 bar pressure reducing valve on its inlet.

In my bathroom I’ve got a 3 outlet thermostatic shower mixer valve, which is fed from the hot water cylinder and the cold mains.

The water from the shower mixer tends to stay cold / luke warm, unless the temper control is turned almost all the way towards hot.

I’m thinking the mains cold might be overpowering the flow from the cylinder due to the pressure difference.

I have tested my mains pressure using a gauge on an external garden tap and seemed to get around 4 bar.

So if the cold mains is around 4 bar and the hot cylinder is being reduced to 3 bar, would adding another 3 bar pressure reducing valve on the cold mains (somewhere before the shower mixer) make any difference to how the shower valve is operating or is the difference between 3 and 4 bar negligible?

Thanks

 

[dilalio]

Cold should be fed to system after the combination valve, before the hot, and should therefore be balanced.
If it is not balanced then, yes, an additional PRV may solve your issue, but it may also be an issue with the thermo cartridge in your shower valve.

 

[Steve1138]

Thanks for the reply.

Yeah, the system was installed by a previous owner of the house and for some reason they didn’t use the balanced out on the cylinder inlet controls for the cold feed to the shower.

It’s not viable to retrofit now as would be too invasive.

My main question is really whether the difference in pressure between 3 and 4 bar (ie cold at 4 and hot at 3) would be enough to cause issues with a shower mixer valve or would the pressure difference need to be much greater for any noticeable issues?

 

[dilalio]

My main question is really whether the difference in pressure between 3 and 4 bar (ie cold at 4 and hot at 3) would be enough to cause issues with a shower mixer valve or would the pressure difference need to be much greater for any noticeable issues?

Balanced feeds are a stipulation for every thermostatic shower valve I have fitted.
Consult the MI's for yours or just go ahead and put a PRV on the cold supply.

 

[oldbutnotdead]

10 metres head difference, or 33%, is a significant imbalance- you may get better results by putting your PRV on the line to the shower rather than to the whole house.

 

[Steve1138]

Thanks all.

It’s not really practical to only fit the PRV to the showers direct cold feed unfortunately (just due to the current location/positioning of everything in the bathroom).

Unless it’s ok to fit the PRV under floorboards (ie on the cold pipe under the landing floorboards, before it enters the bathroom) but I assume it needs to be accessible?

I’ll most likely just install one in the incoming mains feed, just after my mains stopcock & spur to water softener/ outside tap.

Are there any recommendations for a 22mm PRV or should any do the trick?

 

[Gasguru]

As you're only concerned with regulating the pressure when the water is in use then any PRV should do (some valves will limit the pressure with no flow as in the cylinder combination valve set).
Get one that's adjustable and with a threaded port to screw in a gauge.