# Condensing Combi boiler price drop

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• posted on January 22, 2004, 10:12 am

No, just another cost effective approach, using a simple reliable method (could be non-electric controls) of heating water.

A multipoint is NOT a combi. This you cannot understand.

A multipoint has no heating function. It is NOT a combi. It is a single function water heater. A combi is a dual function water heater.

Getting it. As bending valves will be standard in all new houses soon, it is worth putting one on.

Or raise the storage temperature.

It was explained well enough.

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• posted on January 22, 2004, 11:19 am

I was using the term only in the sense of instant heating of DHW with gas, not in terms of detailed functionality and separate circuits.,

Yes I know.

It wasn't clear to me from your explanation.
If you think this has value, please explain again in a little more detail including how it is hooked up.
The multipoint is effectively a "single channel" heater of water. How is that then used in the context of the DHW in its different forms and the heating?
Are you basically saying that there is a circuit of mains pressure potable water between the multipoint and the cylinder and this is circulated by a bronze pump?
Is water drawn from that circuit for "small use" e.g. at the sink?
What happens at the cylinder? Are you talking about pressurising the bulk of the water and then drawing larger amounts from the cylinder (or I suppose the pipework for that matter), or is the cylinder indirect with the multipoint water going through that coil and the larger bulk separate DHW either vented or not? Then AIUI, you are suggesting that the CH is run from an indirect coil anyway, so either this is double indirect if the DHW is split into two entities or single indirect if it is one.
Regarding the multipoint being a simple device with mechanical valve, I lived in one place with an Ascot and another with a Main, and the valves would fail like clockwork every two years and need a new rubber diaphragm.

.andy
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• posted on January 22, 2004, 12:31 pm
wrote:> > Currently multipoints are all regular, I am

The total cost of the main components is low:
- multipoint - 2-port valve - flowswitch - high head bronze pump (the only expensive item) - cheap CH pump - cyl stat(s) - room stat - 200 litre cylinder or thereabouts, part L, or above,
The layout
- From cold water storage tank take a pipe to cold inlet of the shower mixer - Tee off this pipe and go to the Cylinder cold feed - Tee off this pipe and go to the multipoint inlet. - From the cylinder draw-off using a Surrey flange, or from the shower connection on the side of the cylinder go to the hot inlet of the shower mixer. - Tee off this pipe and go to the outlet of the multipoint - just before the shower mixer insert a flow switch. - Between the cylinder cold feed and the tee to the multipoint, insert a high head bronze pump. - on the now "flow" just before the cylinder insert a 2-port valve. - install a cylinder stat (or two to prevent boiler cycling) on the cylinder. Cycling elimination prolongs controls. - Rad circuits off the cylinder coil with own pump and room stat - Could put a blending valve on the cylinder draw-off.
Operation:
- No mains pressure at all. - When the cylinder is calling for heat the 2-port opens and the pump operates. the pressure the pump creates opens the water valve on the multipoint and opens the gas valve. You have heat at 102,00 BTU/hr heating the cylinder directly, giving a zippo recovery rate. - When the shower valve is opened the flow switch detects flow, closes the 2-port if opened energises the pump. The pump pumps through the multipoint, directing all it power to the shower, and also around it supplying hot and cold water. No water goes through the cylinder. the cold side pipe may need a restrictor. or better still a flow regulator on each hot and cold leg of the mixer. - When the shower is off, the 2-port opens back up and it will then heat the cylinder.
Most multipoint have simple mechanical controls with no electrics and no electronic board. Even though with forced flues, which are more efficient, don't have electronic boards. This is a simple system that is very reliable and cheap to install, giving a decent shower and eliminating "water heater" cycling.
Multipoints are designed to be used with fresh potable water. A phosphor de-scaler should be on the system anyhow, as they should be on all systems where scale is a problem..
If multipoints are in the new raised efficiencies, then this setup looks even more appealing.

Of which it is.

They can be changed at every other service. A simple job. Using the multipoint with a thermal store and two cylinder stats reduces cycling, so the diaphragm would get little use compared to just being on the taps. Elimination of cycling prolongs the controls of any water heater/boiler.
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• posted on January 22, 2004, 5:28 am
Andy Hall wrote:

Hmmm, the sort of water heater which has basically a cylinder of water with the burner/heat exchanger running up the centre (so as to heat a large volume of water relatively slowly for storage, rather than a small volume instantaneously) is possibly more promising wrt being made condensing (or even used with flameless combustion).
John S
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• posted on January 21, 2004, 11:40 pm
wrote:

As is the conventional water heater in the USA.
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• posted on January 22, 2004, 12:46 am

Have you seen a typical American water heater?
Complete junk.

.andy
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• posted on January 22, 2004, 1:00 am
wrote:

lower
downward
store
quickly
small
Yes. As described above.

Depends on the maker. Some are well made and condensing.
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• posted on January 22, 2004, 1:28 am

I have never seen any in places like Home Depot, and unlike their clone, B&Q, they have a wide range and sell a lot of them. I've even looked around in the equivalent of plumber's merchants and have not seen condensing products at all.
THey all have energy labels, but when I looked at some specs. the efficiencies were not exciting.

.andy
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• posted on January 22, 2004, 9:46 am
wrote:

Seen any ECO-Hometecs at B&Q these days? Mmmm See any thermal stores or heat banks? Mmmmm
Condensing forced air units are available in the USA. Over here J&S make an adaptor to make the unit a condensing one.
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• posted on January 22, 2004, 11:24 am

No but they do sell condensing boilers as you well know. They are becoming more commonplace at the merchants. To that extent they are widely available.

No, because the general acceptance of them has not reached the same point as yet. Whether it will, who knows. A packaged DIYable one could be interesting for the sheds to sell at some point in the future.

I'm sure they are, but they are not in wide use or availability. I was speaking in relative terms, not absolutes.

.andy
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• posted on January 22, 2004, 11:51 am
wrote:

Few and far between. And only discontinued lines.

The sheds do sell anything that is advanced. they low market quick to sell kit. Anything advanced go elsewhere.

Don't judge the USA by Home Depot (B&Q). Trane and Lennox make top quality kit.
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• posted on January 23, 2004, 12:38 pm
wrote:

quality
US style water heater are available in the UK. Andrews have an add on plate heat exchanger that take hot water from the water heater fir CH purposes.
http://www.andrewswaterheaters.co.uk/index2.html
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• posted on January 21, 2004, 5:39 pm

Yeah I know. The concept is the same however.

.andy
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• posted on January 21, 2004, 5:45 pm

Does a multipoint have a secondary heat exchanger, or does the main heat exchanger directly heat the incoming DHW?
Christian.
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• posted on January 21, 2004, 7:40 pm

Directly heats the incoming DHW.
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Andrew Gabriel

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• posted on January 21, 2004, 11:41 pm

The main heat exchanger. Go to the Worcester Bosch site, they have a piccie of one showing the heat exchanger.
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• posted on January 21, 2004, 5:48 pm

It is not the same. A combi "combines" DHW and CH. The operational principles of some combi's is similar to a multipoint, but few are the same. A multipoint has one large gas to water heat exchanger and a water diaphragm operated gas valve (not 3-way). Most are modulating these days.
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• posted on January 21, 2004, 7:10 pm

I was being facetious. The problem is the concept of heating water directly from the cold mains considering the provisioning of a domestic gas supply.

.andy
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