Pros and cons of combi boilers?



I think your questions 1-5 have been answered by the other replies.

I'm not an expert, but have gone through this myself recently. In making a choice you need to consider many things like cost, installation and efficiency.
Combis: - Cheaper to install. - No header tank required. - Does not need airing cupboard. - Takes longer to fill bath. - Hot water at (almost) mains pressure.
Conventional: - Hot water at lower pressure. - Quicker bath filling. - Showers may need boosting.
There are other types of system which store water at a higher pressure or use stored water to heat the hot water which you may wish to consider.
Mark.
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wrote:

Total nonsense. High flowrate models are available.

Also takes up lots of space. Legionella potential
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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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On Mon, 10 Oct 2005 08:34:12 +0000, news wrote:

Oh no not again. See main FAQ.
--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
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Which on combis is absolutely pathetic. Read my post on this thread on combis.
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Cut and paste against experience? I think not.
--
*Someday, we'll look back on this, laugh nervously and change the subject

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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flatulence wrote in message wrote:> > > Oh no not again. See main FAQ.

<snip senile babblingness>
Care in the community has failed he should be institutionalised.
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<anip>
LOL, you said it! Stop talking about yourself, otherwise the men in white coats will come to take you back.
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You disgusting scumbag. Do not laugh at the afflicted.
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No one gives a flying f*ck about your posts Dribble. The sales of combi's are rapidly plumetting as the benefits of stored hot water systems are being recognised by a generation of people brainwashed by idiots like you. Copper sales are booming too. Now bugger off back into your closet and take a few tablets, preferably the whole packet you sad tw*t.
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OP here. Er, was it something I said ..............? :-))
Thanks to (almost) everyone for the "helpful" comments.
--
Ian

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No. This is the Internet where any insane Looney can have access.

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Yup. And invariably hide behind silly names and false addresses.
--
*I wonder how much deeper the ocean would be without sponges.

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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faltulence wrote in message wrote:> > No. This is the Internet where any insane Looney can have access.

And here we have one. This one is prime example of Internet looniness. Clear he was not chastised as a child.
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So you approve of beating children? Sort of figures. Do you ask your nurse to flagellate you too?
--
*Work like you don't need the money. Love like you've never been hurt.

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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flatulence wrote in message wrote:> > And here we have one. This one is prime example of Internet looniness.

The likes of you.....yes. You did not get beaten enough. Look at how you ended up. A sad case, a truly sad case.
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wrote:

Aaaarrrggh - Doctor Drivel - drivel - kill file - Plink ! Job done !
Nick
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wrote:

looniness.
you
Thank you. Another one who was not chastised as a child.
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Not you, just Dribble :-) , a part time plumbing counter assistant, who is solely responsible for flooding across huge areas of a North London council estate where the gas, water and electricity are still cut off on the grounds of safety. Drivel has a strange fascination with Combi boilers, dismissing storage systems without any regard for the users requirements. Some have put this down to the fact he wasn't breast fed, others to a strange incident involving his mother and a randy plumber fitting a copper tank . True but sad.
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wrote:

It was.
Lord Hall, stop telling lies you Godless person. .
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