Combi boiler - difference in flow rate between hot and cold water

guestiee

Hi, we have a Valliant EcoTEC Pro 28 combi boiler.
We are in the process of planning a new bathroom. It currently has an electric shower and we want to replace with a concealed thermostatic mixer with 2 outlets including a rainfall shower.

I am concerned about the flow rate of the water from the boiler. The cold water tap in the bathroom sink has high water flow, I estimate about 20 litres a min. But the hot tap is at least half of that flow rate. Is that normal? I've read that the hot tap should be similar to the mains water flow.

Thanks for your advice in advance

stragglebod

Sounds about right

11.1 l/m according to the specs.

https://www.vaillant.co.uk/for-installers/products/ecotec-pro-24-28-and-30kw-3776.html

bris

The hot water has to flow through the boiler and be heated as it does. It can't be heated if it's flowing at 20L/M.
The water temp from the mains also need to be taken into consideration so in the winter the flow rate may be reduced further by the colder temp so you need to slow it further to get hotter water.


Combi's aren't ideal if you want fast flowing hot water, they are simply not built for that. Two outlets for hot water at the same time? No they really don't handle that well.


If hot water is an issue then add a tank and change to a system setup..

guestiee

Thank you. Would you expect that flow rate to be satisfactory for a large rainfall shower head and separate smaller handheld head?

ed110220

Guestiee wrote: »

Thank you. Would you expect that flow rate to be satisfactory for a large rainfall shower head and separate smaller handheld head?

I presume you mean for either of the shower heads, not both at the same time?

I have a boiler with a similar flow rate and a Mira Agile ERD shower and it's perfectly satisfactory. Usually I don't even turn it to full flow as that seems unnecessarily wasteful.

jk0

I'd keep the electric shower as a back up IIWY. Then you'll still be able to wash while waiting for the boiler man.

Owain_Moneysaver

The hot water from the combi will be the same pressure. It won't be the same flow.

It will be about 3x as good as the electric shower (and cheaper per litre to run).

If you assume 10 litres/min from the combi compare that to eg this Grohe shower, in their questions they say

At 3 bar pressure, you will get approx 16 l/min from the head shower and 12 l/min from the hand shower

so you wouldn't be able to run that from the combi and get a hot shower in winter.

On the other hand a low flow shower head at 9 l/min should be well within capabilities.