Combi heating a vented hot water tank and other questions

18 Jan 2012
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United Kingdom

We have poor mains pressure (2.5bar and 10l/min at the best). We currently have a Baxi combi boiler which, while fine for central heating, suffers from poor pressure when creating hot water. It will merrily produce hot water from one tap, but if a cold tap is turned on at the same time, the hot water flow stops to a trickle. Now, we are planning on having a new bathroom installed and hope to have a good, powerful shower. To this end we talked to a friendly plumber and he suggested the following:

1) Install a copper hot water cyclinder
2) Install a cold water header tank
(we have room in the loft for both the cold and hot water tanks but he suggested putting the hot water tank either in the bathroom or a bedroom and the cold one in the loft)
3) Install an Aqualiser Quartz Digital concealed with 105mm Harmony head - Gravity Pumped shower which has a built in pump (1.5 bar)
4) Install an imersion heater into the hot water tank
5) Feed the heating pipe from the combi boiler into the indirect inlet of the hot water tank, thereby heating the water in the tank whenever the central heating is turned on and using the immersion heater when we need a top up or the heating is turned off

My questions are really about the planning of this setup; is it reasonable, sensible and logical ? Will the combi really heat the water, and will we get a good shower ?

Many thanks
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Also ... would it be possible to put the hot-water tank in the loft too.. I realise that it would reduce the pressure somewhat (a lot ?), but surely the shower pump would overcome that ?

Thanks Andrew
The pressure is created by the height of the cold feed tank above ground.

However, I would consider upgrading the cold water main into the property if you like the combi otherwise.

Also, if you go for the hot water cylinder route, use a Y Plan which is better for several reasons eg you don't need a bypass.
Upgrading the main ? Is that something a plumber can do, or is it a job for the water company (United Utilities I think)


Them as far as the property boundary, your plumber from there in. If their part is lead, they should do their bit for free.
S plan is better and easier to wire also no need for a bypass as suggested as you boiler has an automatic one built in
Hi, another question.

Does the pressure of the shower depend on where the hot water tank is situated - or is it solely where the cold water header tank is ?

I'm getting another plumber round for a quote and some advice...does the hot water cylinder position matter or is it only the cold water header tank ?

Just the height of the cold water tank.

An S Plan is not better, because it does need a bypass. The fact that the boiler has one is precisely because so many fitters install pump overrun boilers on S Plans without them. As I have posted here before, the purpose of pump overrun is to dissipate residual heat from the boiler into the CH or DHW. An S Plan prevents this, as the bypass just returns this heat back to the boiler. A properly installed Y Plan does not have these difficulties.
Many thanks - I wonder why the other plumbers were so insisitant that the hot water tank needs to be downstairs rather than in the loft
If the cold feed tank is in the loft, the cylinder can be anywhere; near the boiler is usually good.

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