We converted a five bed house in London for students and the plumber
put in a gas Vaillant turbomax plus 828 to serve a shower and a bath.
All the old pipe work from the old conventional system is still insitu
just blanked off. Frankly the combi is just poor; baths are just not
worth having and the shower flow is disturbed so much by washing
machines, dishwashers etc.I thought I could get away with it because we
all know students dont wash but this lot do....
I have read what you all say about combis but think that they are
useless for more than one old lady in a flat, I am afraid.
We now want to put in a an en suite shower room on the second floor,
exactly where the old airing cupboard/immersion heater was. The boiler
is on the ground floor in the kitchen and the existing bathroom is on
I want to put a megaflow or similar unvented storage with an upgraded
The vaillant is nearly new and I wonder if some clever internal
rearrangement will turn it into a sealed system boiler or should I just
bite the bullet and buy a new proper one.
What do you reckon?
There is nothing to stop you using the combi just like a coventional
boiler with water heating driven (via zone valves etc) from the CH side
You could then either not use its DHW capability at all, or more
probably use it either for one of the showers (where it should work well
with no other demands on it to upset things), or perhaps things like
just feeding the kitchen where the (probably) shorter distance to the
taps would save having to run off so much before getting hot water.
You could pension off the combi into just feeding part of the
requirement such as washbasins or sinks perhaps - depending on the
You can then use the CH part of the combi in the same way as any other
boiler to provide heat for the cylinder's heating coil. This
requires a diverter valve, thermostat and possibly a timer/programmer.
No big deal and nothing lost.
Before you do this, however, do check the cold mains flow rate and
pressure and make sure that they are adequate. Typically a combi has
poor performance when its power rating is inadequate for the
requirement - simple physics of heat transfer. However, if the water
flow rate is also low, then a pressurised cylinder wouldn't help and
you would need to use a system with roof supply tank.
Probably better for the clothes / dishes as well these days (modern
detergents and all that). Note though that even cold fill only can still
knacker a shower in some cases. If you mains flow is marginal, turning
on a cold tap will reduce the available flow to the combi causing a
temperature rise in its output.
Exactly. More thought is generally given to unvented cylinder and heat bank
installations. Far too many combi's are just slapped in teeing off the
nearest cold mains pipe for its supply, giving them a poor reputation.
Depends on how it is piped up. And if still a problem you get a proper
combi shower mixer with integral pressure balancer, or fit an external one
on the hot and cold to the shower.
The w/machine and dishwasher can be piped up to take cold only. In reality
the amount of hot water taken from the DHW system is negligible, as most of
the water taken is cold via the DHW dead-leg pipe. Bt the time hot comes
through the appliance is near full of water anyway.
If you have a secondary circulation loop then a hot fill can save money in
In this case, the OP would be better sorting out the pipework, getting the
combi supply dedicated back to the stop cock and piped up as I suggested,
get the appliances on cold fill, get rid of the bath, have a flow restrictor
on the sink tap (available from BES), and put in another combi for the new
ensuite. This is "probably" the most cost effective route for him. I await
his DHW demands.
Unnecessary expense and would take a very long time to recover the
cost considering that dishwashers and detergents used in them are
designed for cold fill and gradual heating, and washing machines,
detergents and clothes are also mainly warm wash only these days.
In other words alter the requirements to meet the limitations of the
combi. This was not what was being requested.
My dishwasher has only a cold inlet. Certain proteins harden when
"cooked", so you wouldn't want to bake them on. (egg for example).
Washing machines may be warm wash only these days, but unfortunately
food is much more colourful than it used to be. So if saturday night's
popadoms somehow managed to eject some lime pickle onto your pure
white shirt, you're going to have problems if you wash it at 40C! That
kind of stain needs a minimum of two washes (or some sort of
non-chlorine based bleaching agent) at modern temperatures.
A secondary circulation pump can also save much money in reduced water
waste. Also it is a great convenience to have hot water immediately at the
taps in any water system.
Nope. Fit the combi properly. The same will apply to any water system; fit
it properly. It is clear this combi was just slapped in. Boy do you have a
strange logic. Must be Little Middle England logic.
That is one issue, the main one in this case. Another is priority of water.
The system should be piped to ensure the shower has little, to no,
interference from other draw-offs.
I'm afraid you and your "plumber", so not know much about combi's. :-)
High flow models are available; I doubt if he has seen one. This sounds a
typical cheapo landlords effort to me. Well firstly I would have properly
assessed the DHW demand. How many people are using this house? Why a bath,
when students only need a shower? A bath takes space and somthing else to
maintain and keep clean.
There are high flowrate combi's around and I would have gone for one of
those. Also I would have arranged the pipework properly. This sounds like
15mm cold water mains pipe snaking around the house and all appliances teed
off this, of which the combi is one. The combi, ideally should have it own
dedicated cold supply from the stop cock, with the cold supply to the shower
taken off this combi supply just before the combi inlet. This way when a
toilet is flushed it doesn't affect the combi DHW.
The same applies to an unvented cylinder regarding the pipework. A 22mm
supply pipe back to the stop cock. Go for a low pressure heat bank rather
than an unvented cylinder. No explosions, and students can do silly things
when drunk, like pissing about with the cylinder controls.
The Vaillant can be turned into a system boiler. That is easy as that is
what it is with a DHW section added.
CH demands? CH zoned? If not is it better to have separte timed zones? A
mains pressure system: combi, unvented, heat bank, is dependent on the flow
and pressure of the mains
Start at the beginning. Give me your DHW demands: number of people in the
house, Number of showers, sinks, size of cold water mains, idea of flowrate,
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