What system do I have and best shower to use...?

[grizzlydoris]

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

 

[John.g]

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]

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.

 

[Deleted member 123817]

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.

 

[John.g]

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]

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.

 

[exedon2]

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.

 

[grizzlydoris]

Thank you for those replies. As I said in my op, we can't have a pump fitted right now (we've been advised that our entire system would need checking and the board replacing before any electrical work is done - can't afford that rn!!!)
There is already a reducing valve fitted in the bathroom.
The current shower is thermostatic - does that make a difference? We did look at getting one without a thermostat (which is what we had originally) but we're advised against it. The thinking was that we would have difficulty setting the temperature, and then it wouldn't react to other water usage around the house meaning we'd get scalded?!

☹

 

[John.g]

Can you measure the shower flow with hot water only on and turned to fully hot?. just run it into a dish/bucket for exactly 1 minute (or 30 secs and then double it) and then measure this into a 1 litre jug to give you the flow rate in LPM.

 

[grizzlydoris]