which combi?

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present combi just gone south and need to replace. It will run 8 rads and a decent shower if poss. Any suggestions from experience as to the most reliable/best performance/economical etc greatly appreciated.
Thanks
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willsniffer wrote:

Our 2 year old 28Kw Vaillant has been problem free and the DHW performance IMO is good - but then we have very high mains pressure here and I don't like the DHW set above 55C anyway...
It's easily more economical than the museum piece it replaced :-)
Only downside is that it's noisy, in that it's "clunky" with the relays and stuff, not just ours either, the neighbours' one is the same.
Lee
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On Wed, 30 Jul 2003 21:28:14 +0000 (UTC), "Simon Stroud"

This is actually the MAN Micromat, made by MAN Heiztechnik in Bremen. I have the non-combi version of this product. Eco Hometec are one of the UK distributors, MHS Boilers being the other. Each stick on their own label (sometimes) and the products are sold directly and not through the trade merchants. Most are sold to self builders and others looking for high quality energy saving products.
MAN is not that obscure, although are better known for trucks, buses and diesel engines. The boiler manufacturing division is a fairly well known player in Germany although not at the same volume as Vaillant.
The Micromat is a well engineered and solid product with sophisticated controls (all microprocessor based so no hardware reliability impact). From an energy perspective it is saving between 25 and 30% as compared to an old Glow Worm.
Not an inexpensive product, but I think very good value for money.
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wrote:

it
can
have
Andy,
Thanks for the more comprehensive summary and a reminder about the Micromat's true manufacturer. By "obscure" I was really referring to the "nobody has heard of it" and more worryingly most plumbers/heating installers that I spoke to when trying to get mine installed had the approach of "haven't heard of that - wouldn't want to touch it". What they probably mean is that they can't get it for 400 down at the local PM and then charge 2500 for putting supplying one - most entertaining.
Regards, Simon.
PS Hope your London meet goes well tomorrow. I would have been there but unfortunately I'll be travelling half way across the country to pick up my new car - that's the slight problem with these deals arranged by a broker. Oh well, it was a good saving.
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On Thu, 31 Jul 2003 06:38:07 +0000 (UTC), "Simon Stroud"

There is a lot of conservatism in that industry. One only has to spend a short time in a heating merchant early morning or late afternoon to hear some of the misinformed claptrap about condensing boilers or anything else other than what they have fitted for the last 15 years.
AIUI, Eco-Hometec mainly sell to self builders, who tend, quite often, to hand pick components for the house and/or are sensitive to eco-issues and to people looking for something better than the run of the mill. MHS mainly has the larger capacity models and I believe sells to projects requiring more capacity or small commercial requirements needing multiple boilers. There is a mechanism to group together multiple Micromats and have the modulating control across all of them. A tip here. The manual on the MHS site for the Micromat is far better produced than Eco-Hometec's translation and especially with application notes and the operating modes described.

Quite. Then there are the loyalty incentives from the large manufacturers like the holidays in Eye-bye-za and monogrammed overalls.
I've always found it curious in the construction industry how everybody has the same name. Mate. In the various merchants they always seem to be on first name terms, which is friendly, I suppose. I was wondering whether it's a derivation from Matthew or something, and whether change of name by deed poll is required before becoming a brickie or heating engineer.....

Thanks for that. Hopefully next time.

.andy
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Andrew Gabriel wrote:

Which probably explains why people have no faith in British plumbers! Did they give any reasoning behind this bizarre behaviour?
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Yes. Some of it was bullshit, but I wanted to hear it so I didn't try and correct anything.
The main reason was lack of reliability and expensive repairs. I can't argue with that -- I don't have the necessary data. Bloke behind the counter said one of the manufacturers was on fourth redesign of condensate drain in a year and third redesign of something else and someone else's heat exchangers usually failed just after warantee and cost over half the cost of the boiler, and the tale of woe went on. Basically, after fitting, they have to keep going back to sort the boiler, which gives the fitter a bad name, so they don't fit them. I asked specifically about the Keston (which I chose) and Ariston (which I looked at because it was the smallest one made). There was some agreement that Keston was probably as good as you'd get now, but ones which are 3 years old are badly suffering failed heat exchangers. Then a comment that whilst it used less gas, it had a 1kW fan in it <bullshit alert> so it just used more electric instead. They were very scathing of Ariston's, but I can't remember why. Also, I presumed from this conversation most gas fitters don't have a flue gas analyser (and when I spoke to Keston, they also assumed the gas fitter wouldn't have one). Reading between the lines, this is why they can't commission or service them.
So, what are the issues? I can believe that boilers based on conventional technology which has matured over very many decades are probably more reliable than boilers based on new technology. There seems to be a problem (or at least a believed problem) in condensing boilers not lasting out or very far past their warantee period without expensive repairs required. I suspect gas fitters have been using the same traditional brands for condensing boilers which they use for conventional boilers, and it seems to me those brands probably aren't the best -- they certainly entered the game late. Gas fitters are conservative (which is not unreasonable when your salary depends on it) and/or gas fitters don't understand condensing technology.
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Some early Ariston combi's were not that hot. The Microgenus is great little boiler and they give a 2 year guarantee with it.
If these fools had the intelligence to look around, they would see that some companies give 3 to 5 years guarantees on all boilers and those with stainless steel heat exchangers invariably give 5 years on the heat exchanger. Glow Worm boilers are now predominantly stainless steel heat exchangers.
You will find that the reason for many heat exchanger failures is that the boiler was not installed or commissioned correctly. In many cases the flowrate through the heat exchanger is far too low when TVRs close down.

Ed will clarify. There are many CORGI certificates. Some for gas installation and some for boiler servicing. If plumber does a CORGI installation course, he may not be licensed to touch the boiler innards.
Some gas cooker delivery drivers are CORGI registered, but only to connect up a cooker with a flexible hose and do a soundness test. Ditto with kitchen fitters who do gas hobs and ovens.

Condensers have been around since the 1950s.
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On 31 Jul 2003 12:25:19 GMT, snipped-for-privacy@cucumber.demon.co.uk (Andrew Gabriel) wrote:

Certainly the heat exchangers are an expensive item, but perhaps this is an issue of manufacturers building to a cost and price point. When I was selecting, I eliminated all but stainless steel exchangers for that reason. I also asked each manufacturer for an extract from his spares pricelist of the 10 most expensive items. That was quite revealing and weeded a few vendors out.

I wonder how on earth they worked that one out.

I think that's exactly it. IIRC from reading Keston's manual, they supply the boiler preset and suggest that the fitter works out the gas rate by timing the meter. They then go on to suggest that the CO2 level is measured to be sure, and of course that needs a flue gas analyser. They then suggest that the fitter calls them if there are problems.
On the MAN boilers the procedure requires a flue gas analyser since the pressure test point that would normally be used on the burner side of the gas valve is actually at negative pressure and not meaningful. There is a procedure with a special test button that is used to allow the CO2 level to be checked at minimum and maximum burn rates, there being an adjuster for each. It is iterative, and takes a couple of goes at each end to get right. The the CO level is checked at each point.
I bought a flue gas analyser in a special introductory offer that BES had last year. Even if I only use it once a year when servicing and cleaning the boiler it pays for itself in two years.
I would have thought that any decent fitter should have an analyser as well - there's really no excuse. Since one of their roles is to look out for excessive CO emissions in an appliance, this is important anyway for servicing. Looking at the flames is one thing, but AIUI only shows relatively serious problems.

Exactly. About 15 years late. The loyalty incentive programs are pretty inviting as well.

This is a shame.
.andy
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Andy Hall wrote:

Especially since the boiler is (should be) fused at 3A !

Owner of a Kane 400 combustion analyser, and loads of 4xAA batteries ;-)
I am installing a Keston C25 in my own home right now.
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wrote:

I'm not sure why heating engineers haven't got flue gas analysers as according to the Screwfix book they're not that expensive. But the guy who serviced our church boiler before we switched to a pair of Kestons two years back hasn't and so far we've followed the (unwritten) advice of a Keston engineer who said that if the boiler was working leave well alone: the design is such that all soot etc gets washed down the condensate drain.
We did have a minor problem with one, traced to a igniter that was arcing down the ceramic insulator. The replacement cost 25, but more to the point took a week. Not a problem in our case with twin boilers but a plumber who had recommended one to a householder (rather than them requesting it) would be getting a lot of stick for doing so, this IMHO, the preference for the common names and models with off the shelf parts.
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Andrew Gabriel

A point here was that the common makes were not the best at condensing technology, although changing fast. Ideal are good.
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His name wouldn't have been Ned Ludd would it?
Do you suspect a conspiracy?
.andy
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wrote:

place
History paints the wrong picture of Ned. The Luddites were not anti-advancement. What they were after was a system that would compensate the 100,000s whose living would be wiped out by the new technology. This was fair demand and the greedy factory owners, who were making millions, and were to make even more, would not pay into this pot. The press obviously sided with the establishment and painted the wrong picture of the Luddites (nothing new there, and echos of the trade unionists jailed by Thatcher to save 1,000s of jobs).
Ned Ludd was hanged. A sad and shameful era in our history.

A commie plot?
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On 31 Jul 2003 08:26:09 GMT, snipped-for-privacy@cucumber.demon.co.uk (Andrew Gabriel) wrote:

That's pretty pathetic, isn't it.
The only reasons I can see for that is if they are still hanging on the old wives tales of the unreliability of early UK manufactured products, or they don't know how to properly fit a condensate drain, or if the set up procedure requires a flue gas analyser.
If it's the last of these, there is really no excuse, they ought to have one anyway since they are only a couple of hundred quid.
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Andrew Gabriel wrote:

At the merchant I use (Peter's Plumbing N11) we have had conversations about which boilers have worked, gone wrong, were good value etc.
The opinion is that only the Keston boiler produces condensate. [I would imaging the MAN would also].
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On Thu, 31 Jul 2003 21:11:35 +0100, Ed Sirett

Yes it does, by the bucketful. Not that it empties into a bucket I should add, but through 22mm plastic and a trap to the waste.
I wonder whether modulating the pump as well as the burner has an impact. The Keston, AIUI, does it by switching a Grundfos pump to one of its three settings.
The MAN has a means of analogue or perhaps quasi-analogue control of the pump (also Grundfos) from 35% minimum up to 100%. From the display on the PC screen when the diagnostic software is run, the pump rate adjusts to the firing rate, but they are not directly linked. I've seen dT between flow and return on occasions of around 25 degrees, so even if the flow is approaching 80 degrees when it's really cold or in HW mode, condensate is produced. There is realtively little visible pluming, even on a cold day. I wonder whether this has something to do with the cylindrical heat exchanger and burner design.....
As I figure it, provided that the change from gaseous to liquid state of the water happens either in the boiler or the part of the flue within the building, the efficiency improvement should be achieved since it is from the heat released by the latent heat of condensation due to the change of phase. The visible "steam" is of course water vapour and already in liquid phase from the latent heat perspective.
Having it condense as water inside the boiler would appear to be more of a convenience in that sense. Most installation guides that I have seen talk about installing the flue such that it is at a slight angle, sloping towards the boiler. I am told that this is mainly to avoid acidic concentrate dripping down walls etc.
Perhaps this explains the "nuisance plume" aspect. If the heat exchanger is rather too warm but nevertheless reasonably efficient and the flue is cool enough, I would expect pluming to occur until the water vapour re-evaporates. This would imply the best efficiencies not being achieved, I think.
.andy
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Andy Hall wrote:

This is only a little less saving than a 'careful' [1] customer who I installed a Keston25 for earlier in the year. In his case the upgrade was from a conventional flued Ideal Concord and very simple timer + plain copper cylinder with (ragged jacket). Finished with Grade 3 Part L cylinder (same size but with a fast coil). All TRV (except bathroom as bypass). Programmable Thermostat.
I think this finally put to rest the speculation about the maximum savings acheivable by installing a condensing boiler.
[1] Notes and files gas bills etc.
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There's no point in a 25% energy saving, if you have to replace it every 5-10 years. The replacement cost for a non diyer is probably >> 1000. There seems to be a total lack of 10 year warranties!! Where are the projected reliability figures? We know that Ideal Concords have a working life span of

Regards Capitol
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Where do you get this notion that boilers have to be replaced every 5-10 years?

Lots of 3 and 5 though.

Don't you know as you are so confident on the lifespan of boilers.

The same for any boiler. Look at a Concord. There is sweet nothing inside. All the kit is outside the case and that is what fails. So this inefficient cast-iron lump just sit there, while the rest does the work.
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