PigletJohn or knowledgeable plumbing people

[GiraffesAreNotShort]

I have a "split" water system, gravity fed hot water and cold feed is all mains pressure. No cold water supply tank in the loft, definitely split.

I currently have an electric shower in the children's bathroom, that is fine. We have an old Mira bar mixer in our en-suite. It fluctuates temperature for the obvious pressure imbalance reasons. We want to fit a digital shower.

Mira say they only cater for a high pressure system or a low pressure gravity. We don't have either. It has to be Mira as we want a ceiling fed digital shower and all the others are very ugly.

Our thoughts were, install a pressure reducing valve on both the hot and cold feed to the shower (pipes run across the loft) therefore we can see what the hot water pressure is and match the cold feed pressure giving a balanced feed. So leave the hot on the maximum pressure it can be and reduce down the cold.

Then we will need a pumped digital mixer as it would then be considered a low pressure system.

Does this sound right?

We are competent DIYers, just need my sparky to connect up the electrical supply to the digital shower. We have installed entire bathrooms/tiled/plumbed etc but this is stumping us. Never had a split feed system before. Any help would be greatly appreciated.

"I have a "split" water system, gravity fed hot water and cold feed is all mains pressure. No cold water supply tank in the loft, definitely split."
Can't be gravity hot water if there's no tank, because the gravity feed comes from a large cold tank in the loft which feeds the hot water cylinder.

As an aside If your header tank is hot then it's an extreme danger (as in they split and dump boiling water through the ceiling)

Regarding the mixer the simplest solution might be too change to a balanced system, cheapest would be both on gravity with a pump, more expensive unvented or Combi.
You can't really pump from the mains and you can't match the pressure on an unbalanced system unless they are connected to the same place. Even a tiny difference will cause an imbalance

Sorry John, I have 2 cold water tanks in the loft, one for the hot water cylinder and one for the central heating, I meant I don't have a cold water storage tank that feeds the taps. I didn't want to confuse anyone with the whole mains fed but I have water storage.

I had a brand new boiler fitted 2 years ago due to ours dying, we did look at megaflow/unvented but went with a traditional boiler. It is a Worcester Bosch Greenstar. Combi wouldn't suit as we have 2 bathrooms. It is a 4 bed house with 15 radiators and we had all the radiators replaced at the same time as the boiler so cost was a factor.

Are you basically saying we can't fit a pressure reducer and then have a pumped digital shower? So that leaves me with a bar mixer and the same issue of fluctuating temperature unless I fit a pressure reducer on the cold feed into the shower.

As John spotted

"We have an old Mira bar mixer in our en-suite. It fluctuates temperature for the obvious pressure imbalance reasons. We want to fit a digital shower. "

But you have a cold-water tank in the loft. It happens, at the moment, to be connected only to the hot water cylinder.,

You can have an extra connection added to this tank, to provide the cold-water supply to the shower. They will then be balanced pressure. you can pump them both if you want. It's a very common plumbing job.

Examine your cold water tank to see what its capacity is. If you are having a pumped shower I expect you will want ten litres per minute or so.

If the cold tank has a 100litre capacity, such a shower would suck it dry after about ten minutes.

BTW bar showers are, for some reason, cheaper and not as good as round mixers.

Thank you PigletJohn. We hadn't even thought of that.

I have done some rudimentary calculations as the tank is unhelpfully not stamped with any capacity. So I work it out to be 2 approximately 25 litres or roughly 50 gallon.

There is space in the loft and room for us to replace this with a bigger capacity tank if needed, which I assume the current tank was sized for only feeding the hot water tank. We know that the draw off on the tank and the fill match fairly well.

*approximately 225 litres

225 litres is more than enough for a bath, so it would be rare to use that much before it had time to refill, unless perhaps you were filling two baths at the same time or in quick succession. "Drencher" heads are notorious for using water very fast.

Ballcoks in loft tanks are usually 1/2" and quite slow to refill. I haven't measured one but I should think less than 5 litres per minute.

Excellent news, you have made our day! We are just looking at a normal riser shower rail and head, no drencher.

I really appreciate your help, Mira technical support were useless.