A 180 litre DHW only heat bank will supply these outlets. This is a
modulating boiler. It think it just maintains a set flow temp, not load
compensation modulation. Ed can confirm he know vaillant very well. If just
maintaining a set flow temp, then have a blending valve on the flow return
to the heat bank. Have it set 10C below full boiler temp, 62C. Have the
boiler set to max temp, 82C.
Have 22mm pipe to the bathtap.
Insert in-line isolation valves on the cold outlets. You can turn the cold,
and hot, outlets down if they are robbing the hot of pressure/flow.
Have a pressure equalisation valve before each shower mixer, or buy a mixer
with an integral equalisation vale. Screwfix now do them.
Things to consider:
- A heat bank can have an electric backup immersion, so if the boiler is
down the shower room will not have hot water.
- When the boiler supplies the heat bank only it will deliver all its energy
into the heat bank. When two showers are being used the combi fed shower
will take the combi's power, and maybe not all of it as it may modulate down
in the process. So some potential energy is not being full used.
- A 210-240 litre heat bank will do the lot. You can then take all hot
draw-offs off the heat bank, and have electric backup. You be able to draw
off 40 litres of hot water. Probably more than your needs.
- But what if the heat bank is down in that the pump fails or a stat is out?
It is worth having the water section of the combi also supply all outlets
(tee into the hot outlet pipe of the heat bank and isert two full bore
valves here). Then if the heat bank is down just turn one full bore valve
off and one on, to switch from the heat bank to the combi. So, backup all
around. The combi will not supply all, but give a decent shower and
excellent supply using up to two draw-offs , but probably not two showes
- The cold water mains. As it comes in, tee into it after the stop cock,
have a dedicated 22mm pipe supply the heat bank and combi (both will not be
on at the same time). The other tee at the stopcock. Take a pipe from this
to the cold taps. An option is fit a 22mm pressure equalisation here instead
of having them on the shower mixers, so the whole is pressure is equalised.
Plumb Center do these.
- Having the water section of the combi idle, will mean it will be very
reliable, as nothing will switching in on a regular basis; it will only be
That is how I would approach it.
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