Combi boiler & Pump for shower

[EricP]

We are having the bathroom revamped and two queries have come to light which I would be grateful for help on. The problems are raised by the guy doing the work for us.

First

I had choosen a Valencia Hydrotherapy Shower Cabin from Victoria Plumb. Just an enclosed quarter cabinet with a row of vertical jets under the shower head.

The story is that these fur up and have to be dismantled to fix them. In other words, mechanically inefficient.

The guy recommends a low level walk through shower.

Second

We will need a power pump for the shower.

(We have a W/B 28 CDi and it blasts the water through our fairly large shower head.)

I do not know our mains pressure but the boiler easily pressurises to

3.0+ if not watching it and most showers seem to like 1.5 bar.

I would have thought trying to power pump a decent pressure mains supply was pointless but I may have missed something.

Cheers

[Muddymike]

We are having the bathroom revamped and two queries have come to light

My initial reaction is to agree with you, but then again a pressure washer pumps water from the mains!

Mike

[John Rumm]

Sounds like a ion exchange water softener would fix that problem...

Why?

You can't generally pump mains water supplies, and there would be little to gain from pumping a combi sourced hot supply.

Which should be more than adequate for pretty much any shower. You are far more likely to run into flow rate limitations rather than pressure ones. Even if the cold main can supply 20+ lpm, the combi will not have the power to heat that volume of water.

Your boiler will be able to heat 10 - 12 lpm depending on the temperature of thee incoming water. So that is your practical delivery limit. If you want a shower with body jets etc it might require more than that.

Indeed, and also against the water supply bylaws in most cases.

If you need a high flow rate of hot water, you would need to install a hot water storage facility (heated from the CH side of the combi), and then pump that (if its a gravity cylinder), or use it directly (unvented cylinder / heat bank etc)

[dennis]

Does it have high pressure jets that don't use much water? Most combis struggle to feed one shower head with a large volume of water so one with six or more heads will have to have a small flow rate from each head. Maybe the need boosted pressure to make then feel OK.

The site quotes a minimum of 1.5 bar but they don't say what flow rate it gives.

[EricP]

Thanks to everyone for the input, particularly John for his usual valuable contribution. :)

[David.WE.Roberts]

Just to check:

If you have a pressurised system then presumably you can only feed the shower at the maximum flow rate of the mains supply. Which you therefore need to know.

The heat store is only supplying a means to provide more instant heat than the boiler can.

If you have serious flow rate problems (or several large showers) then presumably you need a gravity cylinder and then you can pump as much water as you like within reason.

Cheers

Dave R

[John Rumm]

Correct.

Yup.

That's one option, or a mains accumulator. Some combination of the above could also work - i.e. one shower from combi DHW outlet directly, and another from stored water. (note you would need enough stored cold water to match the cylinder size, since you could be using the lions share of the mains inlet capability for the combi in situations like this)