Combi with a hot water tank

14 Dec 2007
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United Kingdom
I have a 4 bed, 1 bathroom, 1 ensuite house and plan to have aVaillant ecoTech plus 937 storage combi fitted. Pressure is 2.5 - 3 bar (working pressure 1.5 bar - what is the difference?) and when measured at our kitchen cold tap we get 11 - 15 litres / min.

if we measure flow at the 22mm mains inlet to the house we get 20 litres / min

I am concerned that I will not get a decent shower? Want at least 11 litres / min.

I have been told that you can add a hot water tank that will be heated by the combi and use this (and the existing cold water tank that we will keep) with a pump to power a shower. Is this right and how does it work i.e. can you just have the tank heated up without the central heating being on?
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By creating a new "heating" zone which actually goes to the cylinder using motorised valves [Lets call it zone2] you can turn off the valve that feeds your heating system [zone 1] and turn on the valve that heats up your cylinder circuit [2] to get hot water without the radiators heating up although obviously your boiler will have to be turned to CH for it to work.
You can do this but it would be silly for a shower.

You would be better off using the water tank and cylinder for the bath supply and use the ecoTEC 937 for showering. That way, no pump is involved.

We always try to avoid designing a pump into the hot/cold system, they create noise and are not hugely reliable.

If I were you, I would put the ecoTEC937 in and see how you get on, the showering will be first rate looking at the figures you have provided.

If you intend to use more than one 11 litre shower at the same time you need to look at either;
-upgrading the water main and fitting an unvented cylinder with an ecoTEC 6 series
-same as above but use an accumulator instead of the water main
-Or fit an ACV Heatmaster with an enhanced water supply (35l/m output).

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