Combi boilers - latest models?



house,
in
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 excelent. 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
Regards Jeff
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wondered
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on
They are selling well.
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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 boiler FAQ.
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
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I posted a comprehensive post on combis, that could go in the FAQ. Here it is:
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 CD50.
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. http://www.alpha-boilers.com/products/CD50.html
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 priority.
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Sirett wrote:

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.
--
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Free SEDBUK boiler database browser http://www.sda.co.uk/qsedbuk.htm
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