Actually mains supply at the moment is from a 4 house shared lead pipe via
15mm Hep2o (due to severn trent taking their time)
Performance re bath filling is the same as the old tank system except that
the hot water never runs out (obviously when another tap is used the flow
takes a big hit)
So when my nice shiney new 25mm pipe is connected it should be bordering on
Thanks Dr D for recomending the cd50, your recommendation + my plumber
suggesting it sealed the decision - btw my builder is that impressed he's
getting one as well
On Mon, 05 Dec 2005 01:08:09 -0800, r1chardowen wrote:
I have been fitting a number of Vaillant Ecotec Pro 28s. These
are reasonable units. These are £855 all in with the VAT and the flue.
The Ideal, Glow Worm, Bosch-Worcester are perhaps just as good.
One day I may get sufficient round tuits to write the how to choose a
Work out what you really need/ are prepared to put up with for the flow
rate you may find need something different.
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
I posted a comprehensive post on combis, that could go in the FAQ. Here it
Here is a run down on combi's:
Firstly, a combi is a "combination" of the heating and water system in one
case, eliminating external tanks and cylinders, and generally supply hot
water at high main pressure. To confuse a little, some can run at very low
pressures and even off tanks. Generally most are fed from the mains. It is
generally a matter of mounting the boiler and connect up the pipes. The
expert designers have done the hard work for you and put all in one case.
Types of combi:
1) The Infinitely Continuous Combi -
Heats cold mains water instantly as it runs through the combi. It never runs
out of hot water. This is the most common type of combi, generally having
lower flowrates than Nos 2 & 3 below. The largest flow rate instant combi is
a two bathroom model, 22 litres/min ECO-Hometec. Being a condenser it is
very economical too. http://www.eco-hometec.co.uk
2) Unvented Cylinder Combi -
An unvented cylinder is a similar to a conventional cylinder but run off the
high-pressure cold mains. A combi with an integral unvented cylinder has
approx 60 litre cylinder heated to approx 80C, with a quick recovery coil
that takes all the boilers output. A fast acting cylinder thermostat ensures
the boiler pumps heat into the cylinder ASAP with a recovery rate from cold
around 5-8 mins (Ariston claim 8 mins). The 80C water is blended down to
about 45-50C. e.g's, Ariston Genus 27 Plus, Glow Worm, Powermax, Alpha
3) Infinately Continuous/Unvented cylinder combi -
An example being the Alpha CD50, a combination of both having a two stage
flowrate, of high flowrate when using the stored water with an automatic
flow regulator switching in to reduce flow to an infinately continuous
flowrate of approx 13-14 litres/min.
4) Heat Bank Combi -
Incoming water is instantly heated running through a plate heat exchanger
(as is most instantaneous combi's) that takes its heat from a "domestic hot
water only" store of water at approx 80C (instantaneous combi's take the
heat from a heat-exchanger heater via the burner). A fast acting thermostat
ensures the boiler pumps all of its heat into the store ASAP with a recovery
rate about 5-8 mins from cold. The 80C water is blended down to about
45-50C. They are generally two stage flow rates, in that when the thermal
store is exhausted it reverts to what the burner can produce, which is
approx 11-12 litre/minute. e.g. Vokera & Worcester floor standing models
(standard washing machine sizes).
N.B. The heat bank is a variation of a thermal store, but is "not" a thermal
store in the conventional sense in that a coil carrying cold mains water
runs though a store of hot water kept at about 80C. Heat-banks are far more
efficient and give higher flowrates than conventional coiled thermal stores.
The stainless steel plate heat-exchangers do not scale up so easily.
5) Combined Primary Storage Unit
(Not classed as a combi, but a derivative of a combi, but still a one box
solution, so still in the same family)
These are a combination of a large thermal store, or heat bank, and boiler
in one casing. The units are large (larger than standard washing machine
size) and floor mounted. The heating is taken off the thermal store, which
in many cases the DHW taken off the store using a plate heat-exchanger
(heat-bank). Unlike the Heat-bank in 3) above the thermal store supplies
heating "and" DHW, giving the "combined" to the title. They are available
from 1 to 2.5 bathroom models. Gledhill do an excellent condensing
version, the Gulfsream 2000. http://www.gledhill.net
Nos. 2), 3), 4) & 5) have high flowrates. No. 1 "generally" has low
flowrates but there are always exceptions and some can be high - e.g. the
ECO-Hometec infinitely continuous combi, actually has a very high flowrate.
Nos 2), 3), 4) & 5) use stored water, but in different ways. Unlike No. 1
"some" versions will eventually run cold, but that takes quite a time, hence
some are referred to as "two bathroom" models, having the ability to fill
two baths with very fast recovery rates. As hot water is being drawn off
the high rating burner is also reheating. Very rare do these combi's run
out of hot water in average use. When taking one shower the burner may be
re-heating faster than what can be drawn-off. No. 3) above uses stored
water but will not run out of hot water (high and low flowrates). Most
versions of No. 4) above are two stage flowrate models (high and low
flowrates) and will also not run out of hot water.
There are combi models that give hot water and heating simultaneously as
Combined Primary Storage Units do. Most don't as they are hot water
I've got a Glow-worm 24Cxi combi - runs excellently but whoever designed
it was not a service engineer. With a little rearrangement of components
and the use of a couple of wing nuts you could remove the condensate trap
for cleaning without any tools. Instead it's a fight to get it out: first
remove the ignition then try and unscrew a screw that's been placed so as
to be impossible to undo save with a screwdriver bit and 1/4" OE spanner.
Do. (but not quite as bad) the ignition electrode screws on the Keston
Celsius - in the factory they obviously go in before the flue hose. Which
makes getting them out harder than it should be.
Tony Bryer SDA UK 'Software to build on' http://www.sda.co.uk
Free SEDBUK boiler database browser http://www.sda.co.uk/qsedbuk.htm
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