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Discuss What system do I have and best shower to use...? in the DIY Plumbing Forum area at PlumbersForums.net

Messages
1
Hi,
I really need some help with a shower replacement please. Long story short, our 1950s house had a mixer shower fitted donkey's years ago that apparently ran from the mains and wasn't 'allowed' anymore, we never had any problems with shower temperature or pressure. Our bathroom is downstairs. We had a new bathroom fitted and mixer shower replaced, there were endless problems with pressure (often not much more than a dribble if you wanted warm water). A restrictor valve of some kind was fitted to the cold water which helped a tiny amount. Three replacement mixers were fitted and eventually we had satisfactory pressure with the last one (the plumber of 30 years said he'd never experienced anything like it before and if this shower didn't work then there was nothing else he could do). Move forward 4 years and that mixer has pretty much fallen apart and needs replacing - I don't know where to start!!!
We have a cold water tank in the attic, gas boiler for CH/water on the ground floor and immersion boiler also on the ground floor. The cold water from the bath taps is very high pressure, the hot much lower.
So.... what kind of system is this please?! We've been told it is gravity-fed AND mains fed?!?!
What kind of shower is best? We cannot at this time have a pump / electric shower fitted. Is there a more 'heavy duty' mixer shower that can cope with this mess? Or, would fitting a shower to the bath taps be the best solution?!?!

Please help! I only want a warm shower with decent pressure, nothing fancy!!!
Thank you in advance,
Tracy
 
Messages
1,934
You probably had/have gravity fed hot water and mains fed cold so unless both at the same pressure then no real mixing. The pressure from the gravity hot should be ~ 0.5 bar static so the mains would need a pressure reducing valve (PRV) that is capable of reducing the pressure to 0.3/0.4 bar to allow the two to mix. I think pressure balancing valves are also available, some on here will advise, it should then work IMO.

Is your mixer thermostatic?.
 

Timmy D

Gas Engineer
Messages
443
You probably had/have gravity fed hot water and mains fed cold so unless both at the same pressure then no real mixing. The pressure from the gravity hot should be ~ 0.5 bar static so the mains would need a pressure reducing valve (PRV) that is capable of reducing the pressure to 0.3/0.4 bar to allow the two to mix. I think pressure balancing valves are also available, some on here will advise, it should then work IMO.

Is your mixer thermostatic?.

Just adding that you’ll struggle to get a prv down to 0.5 bar. At the low end, they typically bottom out at 1bar.

I’d be looking to fit a pump on the hot.
 
Messages
16
Probably correct Timmy but seems a pity to have to install a pump on the hot especially since it has a relatively decent gravity head.
Would it be daft to just fit say a 3mm orifice in the cold supply, the shower TMV should then work ok as the differential pressure will be much reduced once the cold water starts flowing, would also require a NRV in the hot supply.
 
Messages
1,934
If a PRV is fitted and assuming it works down to 1 bar then as the hot side shouldn't be < say 0.3 bar when flowing, one would think that a shower TMV should operate with a deltaP of 0.7bar without any problems.
 

Ben-gee

Esteemed
Plumber
Messages
2,051
Single impeller pump on the hot, measure the incoming main pressure and match the pump to this. If incoming main > 4bar, fit prv on main and dial it down.
 
Messages
506
Probably correct Timmy but seems a pity to have to install a pump on the hot especially since it has a relatively decent gravity head.
Would it be daft to just fit say a 3mm orifice in the cold supply, the shower TMV should then work ok as the differential pressure will be much reduced once the cold water starts flowing, would also require a NRV in the hot supply.
I'm afraid that won't work all you do by reducing to a small orifice is reduce volume not pressure, indeed you would probably accelerate the water due to vortex effect.
Ideal made a shower using this principle (trevi boost?)
As has been said pump the hot enjoy decent flow on hot through the house.
 

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