Can I run a mixer shower CW feed from a tank?

[scotster]

We are having a 1st floor shower fitted with a termostatic mixer and I was wondering if we could feed the CW from an existing loft tank?

Reason is that we are on a combi with not the best CW mains flow/pressure in the world and if the incoming CW mains has to feed both it will be a bit of a dribble. The CW tank would only be used to feed this shower as its an old one we no longer need.

I see the only issue if the tank empties...
Would the thermostatic mixer cut the flow if it lost all cold flow?

Is this a regs no-no or just not good practice or is it OK??

Thanks for any helfpul advice!

Rgds, Scott.

 

[lifesagasman]

it's not a viable proposition. i'm out

 

[scotster]

Thanks for such a prompt and polite reply.

"do you know anything at all about plumbing? "

Did I say I knew anything about plumbing? If I knew the answer I wouldn't be on here seeking the advice of plumbers (also voluntarily on the forum) who I assumed would be reasonably happy to help without requiring a qualification of my ignorance.

If it so pains you to answer such stupid questions then please feel free not to do so in the future.

S.

 

[lifesagasman]

i'm usually more helpful but it's late and i'm feeling peaky

 

[Nige F]

We are having a 1st floor shower fitted with a termostatic mixer and I was wondering if we could feed the CW from an existing loft tank?



Thanks for any helfpul advice!

Rgds, Scott.

I kind of read that as the thermo mixer is already bought/ ordered . Unfortunately it won`t work and I would think the best option would be a pumped electric shower . Pump is hidden in casing - feeds from cold tank. Electric is 9+kw. It` s like a mains water fed one but exactly for your low mains pressure scenario. Best I have so far

 

[scotster]

No worries lifesagas.

We haven't bought anything yet so anything is possible.

Let me just clarify that the CW feed is around 14l/min and combi feeds out a good flow rate when its just feeding one tap - not sure on pressure as I cant measure it but its not a geyser..

I was trying to avoid a traditional mixer shower (we wanted a nice unit with just the adjuster knob on the wall) that pulled from the combi and the mains CW effectively both using a limited CW supply.

I dont know if that changes the scenario. I assume that it doesnt for a thermostatic mixer as the HW is at mains pressure (or whatever the combi puts out) and the CW woudl just have the head of one story from the loft tank? Is the the issue?

Does the electric pumped shower ONLY take a feed from the CW tank? That sounds lilke a plan. ONly problem will be potentially how they look......

Is it not possible to use a mixer shower and put a pump on the CW tank feed? Thwe HW feed from the combi on the other feed? That may be a stupid idea but Im not a plumber!

 

[dextrous]

To be honest, it may well be that the water pressure/flow rate you have will be fine for a shower anyway. I'm struggling to think how a pump attached to the cold water tank will be able to equal or better the mains that you have. Also, unless you really do have a problematic mains supply, in which case a combi wouldn't have been installed in the first place, an electric shower will be far inferior to even the worse combi fed thermostat.

However, in specific answer to your specific question, the trouble you will have will be ensuring that the mains pressure and the pressure from the pump are equal. If they are not, then one will prevent the other from flowing properly - we have a lot of problems on here about mixers that have mains fed cold and gravity hot. Your's will end up giving the same problems for the same reasons

 

[scotster]

Thanks Dextrous.
So mixers arn't good at imbalance pressures? That suprises me a bit as you say I imagine a lot are HW from Cistern and CW from mains.

I'm off to screwfix to buy a pressure gauge....

What would happen if the tank ran dry in any of the above scenarios? Do the mixers cut off the shower?

 

[dextrous]

If the cold water ran out, the thermostat would keep running, but you would get a burnt head (or worse ) - they don't have safety cutouts.

As for themostatic showers working in houses that have gravity hot water, then these are often supplied by using a twin impellor pump, so both the hot water and cold water are got from the same supply (the cold water tank). Another solution has been the venturi type shower - which uses the pressure from the cold to draw it out of the hot - this may work in your case, but I can't be sure since it's designed (the inlets) with hot being gravity, the opposite of what you propose.

In any case, what you have to be careful of is backflow of hot water into the cold water tank, which could then overflow taking your hard earned cash (used to heat the water) with it - thus check valves are needed.

 

[scotster]

Very helpful dextrous.

I'm going to do some testing so I get the basic information needed. I

t sounds like the electric pumped shower from a the tank may be the way forward. Do you know if you can get 'concealed' ones where all the pump and heater are hidden? I know you can get conventional electric showers like that - at a price.

What do I google?!

S.

 

[dextrous]

Must admit, I don't know if it would work but you could investigate using a twin impellor pump so you get both hot and cold water supplied via the cold water tank, an instantaneous water heater (bit like those under the sink ones) and a thermostatic mixer shower.

Still reckon that none of this will be necessary! Here's hoping

Out of idle curiousity, what part of London are you in?

 

[scotster]

Thanks Dextrous.

I live in Ham which is inbetween Richmond and Kingston.

 

[dextrous]

Chiswick lad myself originally. Was asking since to my knowledge, Ham isn't reknowned for low water pressure.

 

[scotster]

For me its all flat-lander as I'm from Sheffield......