Central heating boilers. What make?

[Doctor Drivel]

Matt, I have not had a water cut for countless years - oh one for 10 minutes.

[Andy Hall]

On Tue, 11 Jul 2006 00:45:00 +0100, Doctor Drivel wrote (in article ):

However, check the cost. I was quoted £3k for this and then it would have taken a further £2k to reinstate the drive.

"Once" could be expensive.

[Doctor Drivel]

3K to replace a mains pipe? Sounds too steep. Main replacemnet is nver this expesnive, unless you are up a 300 yard drive. You do all the work yourself (digging). and leave the pipe above ground and they come and connect.

[Andy Hall]

On Tue, 11 Jul 2006 13:09:31 +0100, Doctor Drivel wrote (in article ):

That was the price from several suppliers because of complex routing and reinstatement.

Main replacemnet is nver this

I am afraid it is.

You do all the work yourself

I don't do heavy digging.

However, even on a DIY basis, this would take a lot of time, as would the reinstatement.

Whichever way you look at it, the time, the inconvenience and the cost are considerable items and not something that can be disregarded.

[Ed Sirett]

It's probably time you had a look at the boiler choice FAQ and the heating section of the main FAQ.

[Doctor Drivel]

I would say give it a miss as it's 20 years out of date. Get it updated.

[Dave Plowman (News)]

Indeed. And the possibly uprated gas main for that 'high flow' combi. But of course dribble doesn't worry about spending money. Provided it isn't his...

I've a feeling even a new 22mm water main wouldn't provide enough flow in this part of London where the pressure is at the minimum.

[Doctor Drivel]

Oh my God. A domestic gas meter can supply 62kW

[Willi]

what the differences & pro's & cons are now of the different system types. In a nutshell " You have give me all the clues" Thanks all. Regards, Will

[Ed Sirett]

You have made this comment several times of late. I would be happy to update the FAQ if you could be more specific. To put it another way which aspects of domestic heating technology that have changed in the last 20 years are not covered in the BoilerChoice FAQ? Is there something which is so glaringly wrong it needs correcting?

If, however, as many might suspect, you are simply slating the FAQ for not over-whelmingly endorsing combis then the FAQ will stand as it is. Both the main FAQ and the Boiler Choice FAQ set out arguments for and against and explain the matter is not an open and shut case.

[Doctor Drivel]

Here is the post. The FAQ parts in quotes.

Or may not:

"Vented HW cylinder. This is still the norm for most houses. With a modern cylinder and correct controls there should be no problem with running a bath every 15-20 minutes. Cylinders are now required to have a good level of insulation (not the old jacket insulation). New replacement cylinders will be able to heat the whole cylinder from cold in around 20-25minute,"

20 to 25 minutes? Only a quick recovery cylinder can do this. The normal Part L is rated at 30 minutes warm up if all criteria is met in boiler temperatures, flow, etc. A quick recovery with a condensing boiler can reheat in 10 to 15 minutes depending on boiler size. They also enhance condesning efficiency. There is no mention of quick recovery cylinders in this FAQ.

"Unvented HW cylinder: Offers HW at mains pressure together with excellent flow. These are expensive and can only be installed by qualified people. To justify the expense you really need to have an excellent water main at least 25mm diameter plastic pipe. Results will be adequate but probably not worth the cost if used with an ordinary lead or 20mm plastic incomers. "

The all important annual service is omitted. It will cost £60-100 a year to have serviced. That is over £2,000 over 20 years. They also have the potential to explode:

"Thermal store: Offers most of the advantages of the Unvented cylinders, costs are similar but may be diy installed. The flowrate is still pretty good (around 20 litres/min). Can be used to integrate other sources of heat (solid fuel, solar) or facilitate underfloor heating."

No mention of the heat bank variant of the thermal store (Heat banks use plate heat exchangers, stores use coils), which can give flowrates of 40 litres/min or more.

"Normal combi boiler: Heats water only when it is needed. Instant availability (after the HW has drawn through and the boiler settled down - about 10-40 seconds). Never runs out. Simplified installation. Rather limited flow rate. "

Know as an "infinitely continuous" combi, not a normal combi. Some models have very high flowrates that fill baths very fast indeed, and can do 2 bathrooms (MAN made in Germany), although these are not available in the local plumbers shop being special order.

"Small storage combi: As above but holds a store of HW to give a prompter response and improved flow rates for a while until the stored HW has run out. "

The above are to eliminate the combi lag at the taps, giving faster hot water. This was not explained.

"Large storage combi: Washing machine sized floor standing combi boiler. Contains pretty much all of the benefits of a HW cylinder whilst still having a simplified installation. Saves the space that a HW cylinder would take. There are multiple decisions to be made based on trades-off between size, cost, flow rate, warm up times etc."

Some are larger than washing machines sizes. Some can supply three baths (Gledhill Gulfstream), ACV Heatmaster. All have no cold water tanks.

No mention of high flowrate wall mounted combis like the Alpha CD50, which is a mix of the infinitely continuous combi and a stored water combi. It is a two stage flowrate (high and low) and never runs out of hot water.

No mention of high flowrate multi-point water heaters like the Rinnai and Andrews (relatively new innovations in the UK), which can also be fitted outside saving much space inside a house, and do two bathrooms. A small CH boiler and an outside high flowrate Rinnai will be about the same price as a boiler and an unvented cylinder, probably less, and takes up no space in the house and never runs out of hot water. And if the boiler is down the DHW still runs. Also no troublesome CH zone valves on the CH system making a simpler and more reliable installation. Rinnais have interior models too. Rinnais are ideal for multi-jet showers (a newish innovation). An unvented cylinder would have to be "very" large, and expensive, to compete with the output of a Rinnai.

This FAQ is misleading and omitting information of modern equipment and ways gives a distorted ill-informed view. I would not recommend people take this FAQ seriously as it is only applicable to 1986.

[Ed Sirett]

The relevant standard mentions times around 20 minutes - for Part L compliant cylinders. Suggestion not upheld.

The potential to explode is eliminated by having the only possible method of heating which could cause a problem (electricity) to have two thermostats (one of which locks out) also there are two pressure relief valves, and one temperature relief valves.

There is no manadatory requirement to have the unit serviced and frankly the guarantees are either so limited or never likely to be needed.

It is possible to create a hazard by incorrect installation as indeed it is with a vented cylinder (I've seen one this year with a valve on the outlet vent pipe).

NO change.

Too much detail. Splitting semantic and linguistic hairs is not my style. I might add "at least 20 litres/minute or more".

"Normal combi boiler:

I think the explanation says 'prompter response' - how is that a failure to explain. Much of the lag is the pipe work and such a boiler will not make any difference to that aspect.

Covered by the term 'simplified installation'.

Covered by the comment about a 'spectrum of models'. I might add ...typically a large floor mounted unit although some are wall mounted ...

The FAQ is written to help a variety of people including those who might not even know about a combi or a condensing boiler (or might even believe those terms were opposites).

The FAQ does not contain the very precise and detailed descriptions of the slightly different shades of combi boiler (some of which are much more functional than many people may have experienced).

If in a thread it turns out the the discussion can usefully delve into these matters that's fine. The purpose of the FAQ is save time and effort by answering the _bulk_ of the questions so that the effort can be focused on specifics in a thread.

You are welcome to write you own comprehensive guide to combi boilers and host it yourself.

[Doctor Drivel]

NO. Maximum 30 minutes, most go slightly better to keep with Part L. Gledhill say: "British standard A cylinder/tank to this standard will have an approximate re-heat time of 25 minutes with a suitable boiler and a pumped primary circuit."

Quick recovery cylinders are a reality and popular and "enhance condensing efficiency" at the same time "downsizing an existing cylinder". In most cases the owner never runs out of hot water as the boiler is replenishing as fast as it can be drawn off.

These need mentioning as they are there and relevant. The two relevant points are in quotes.

The potential to explode is NOT "eliminated" It CAN explode. The potential is "reduced" by safety features. People need to be aware of the dangers and that unexploding versions are avialable giving identical performance, such as vented thermal stores and heat banks.

"Every" makers have them annually serviced. If not the insurance will not pay up in a claim. Gledhill say: "Unlike unvented cylinders BoilerMate A-Class does not require an annual service"

The regs recommend a service and the makers insist on one.

Also look at this:

must be made aware of the extra annual cost to maintain this potential bomb. "There is an extra cost".

The FAQ is not about incorrect installations at all. Focus on what it isn about. You are irresponsible and need to learn more about unvented cylinders. Your word "eliminated" is indicative.

That is irresponsible as the average heat bank can deliver 40 litres/min. TWICE what you say. A minimum of 20 litres is misleading. Thermal stores and heat banks are different, even if you think they are not. The DHW take offs is very different indeed. The only thing they have in common on the DHW front is stored hot water to transfer heat.

Too vague. Combi lag at the taps is more in keeping with what people understand. Know your audience and those reading will be novices.

You don't even mention that either.

Not covered at all. 'simplified installation' is too vague. You say washing machined sized, only two are, with most being larger, and many can deliver 3 baths and over, whch is very different to a single bathroom job. People need to know the range of flows which these combis can deliver. Yes one can do 3 baths, which is highly significant - you have no mention of such power, just open vague comments. It is a FAQ!!!!! Highlighting the types and sizes and what they can deliver is not that difficult.

Now that says a lot!!! Are you serious, or taking the piss? An FAQ is to explain.

The point is that some wall mounted models can give cylinder performance. Floor mounted models may give higher performance. The stored water models don't always run out of hot water with a few having two stage flowrates, so NEVER running out of hot water - all applicable to when choosing a model. No mention of it all, just some cover all vague term.

Best add what I suggested.

Yep.

It is so lacking and out of date it is misleading

The questions which you think is relevant, but your mind is in 1986.

You have totally dismissed the Rinnais. For Gods sake!!! They are superb for full body jet showers, which are catching on like widfire, replacing expensive large cylinders...and can be fitted "outside" too. Two recent innovations to the UK that can add value, and not mentioned and you don't think it relevant either. My God!

You asked me for input. I am giving it. Now develop an attitude resenting the significant and relevant suggestions.

If you do not incorporate my relevant suggestions. PLEASE DROP THE FAQ. It is misleading. It comes across a very amateurish.

If it is not changed I will continue to tell people to ignore it, as it is vague and lacks information of modern innovations. No one can make a reasoned choice from it only the choice you think is applicable, which revolves around 1986..

[Phil Addison]

[snip highly antagonistic critique of Ed's "Choosing a Boiler FAQ"]

Mr Drivel...

It takes a lot of time and thought to produce a comprehensive FAQ. Very few come out fully formed and almost all start off as few paragraphs aimed at answering some basic questions. Then they can be built upon.

Whilst I might agree that Ed's FAQ does not cover the whole range of options it IS a very good introduction. Bear in mind it is written voluntarily in his own time and he PAYS for the webspace. It is very easy to knock things, but not so easy to write coherent text that contains complete and error-free information. You of all people should know that.

Try giving your comments in a more friendly and less aggressive way, and you might find they are more readily accepted.

Phil The uk.d-i-y FAQ is at

Google uk.d-i-y archive is at NOSPAM from address to email me

[Doctor Drivel]

"Phil Addison" wrote in message news: [e-mail]...

That's me.

It is 20 years out of date, which I have told him. He asked for me input, I have given it. He has basically rejected the lot. The FAQ as it stands it pretty useless for a novice to grasp in parts as he is using catch all phrases which are meaningless to a novice.

Things have moved on in 20 years - the introduction of the plate heat exchanger to domestic appliances as led to great leaps in instant hot water in combis and heat banks. Most boilers sold now are combis - a FACT. About

1 million boiers are sold each year with combis being 60 to 70% of sales. The "traditional" boiler now is the combi. Mains pressure hot water is the prime way ahead, if the mains pressure and flow is good enough a mains pressure system is the first choice, whether combi (of various types), heat bank, thermal store or unvented cylinder. Combis (the floor mounted jobs) can even supply up to 3 baths. Instant hot water doesn't cover all as it is mains pressure and flow dependent, so the older methods of stored water have to be covered too. That is the way it is. That is way it is going. An up to date FAQ must cover the choices merely stating what is available. It doesn't it whitters on about yesterdays technology and methods and approaches.

I have highlighted some relevant innovations that are highly useful. Ed, no doubt has never seen an Rinnai or Andrews multi-point, so he dismisses them out of hand - not down the local merchants guv so can't be right. These high flow Japanese appliances are a God send to some homes being fitted outside if you want and doing two bathroom too - superb for increasingly popular multi-jet showers (even B&Q sell them). Stay in a multi-jet for not too long and you will run out of hot water on a normal cylinder, a Rinnai will supply the needs, and cheaper than massive space taking unvented cylinders with their £100 annual service charge - which Ed thinks is not relevant, yes. That is just two innovations that have come to the UK recently, which the FAQ does not even mention.

For dismissing the combi myths and giving the levels available look at below. I have periodically posted a comprehensive post on combis on the group, 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. The case could be small and wall mounted or large and floor mounted, but a "one-box" solution. 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.

Combis are rated by DHW "flowrate". The CH side is generally large enough to heat a 5 bedroomed house.

Types of combi:

1) The Infinitely Continuous Combi -

Generally gives low flowrates with exceptions giving high flows. The low flowrate models fill bath slowly but excellent for showers. 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. Typical flow rates are 11 to 12 litres per minute, with some 40kW versions giving around 15 litres per minute. The largest flow rate instant combi generally abailable in the UK is a two bathroom model, 22 litres/min ECO-Hometec. Being a condenser it is very economical too.

The largest flow rate model is the special order wall mounted MAN Micromat at 76kW which requires a commercial sized gas meter.

Some models may have a small 10 to 15 litres store of water to prevent the "combi lag" at the taps. Water is delivered to the taps at the same rate as an cyldiner system. Other models keep the internal plate heat exchanger hot to eliminate the "combi lag".

2) Unvented Cylinder Combi -

Gives High flowrates. 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 a 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, wall mounted: Ariston Genus 27 Plus, Glow Worm, Alpha CD50. Floor mounted: Powermax, Ideal Istor, ACV HeatMaster (unvented cylinder/thermal store hybrid), Geminox.

3) Infinitely Continuous/Unvented cylinder combi -

Gives High flowrates. A wall mounted example being the Alpha CD50, a combination of both having a two stage flowrate, of a high flowrate of 18 to

19 litres per minute when using the stored water with an automatic flow regulator switching in to reduce flow to an infinitely continuous flowrate of approx 13-14 litres/min when the stored hot water is exhausted. models on sale now tend to have this two stage function.

4) Heat Bank Combi -

Gives High flowrates. Incoming water is instantly heated running through a plate heat exchanger that takes its heat from a "domestic hot water only" store of water at approx 80C. This store of water is "primary" water, water that stays inside the system at all times - the water is used to store heat. A fast acting thermostat ensures the boiler pumps all of its heat into the heat 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. All floor standing models: Vokera & Worcester-Bosch (both standard washing machine sizes), Viessmann 333,

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 as the plates flex.

5) Combined Primary Storage Unit

Gives High flowrates. 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 3 bathroom models. Gledhill do an excellent condensing version, the Gulfstream 2000.

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. Most models have two stage flowrates so hot water never runs out. As hot water is being drawn off the high rated 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 a few combi models that give hot water and heating simultaneously as Combined Primary Storage Units do, using two pumps. Most don't as they are hot water priority.

[Dave Plowman (News)]

Because it's cheap and cheap to install - as well as possibly saving some space. But this certainly doesn't make it the ideal solution. As the poor performance of *the majority* of combi installations, hot water flow wise, bears out - no matter how you rant and rave about 'high flow' types. Because those who can only afford a standard combi installation just ain't going to find the money for a better one. And that's where the cost effectiveness of a storage system comes in, because it often already exists.

Oh sure. Where turning on any tap in the house - or flushing a loo - effects the hot water flow. *Very* high tech.

The FAQ gives the basics as apply to most. For expensive high tech alternatives you can always ask here - as no FAQ will ever be bang up to date.

Just how many want two boilers with the initial costs and servicing requirements that brings? Again, a specialist requirement and not really neccessary for a DIY FAQ.

You as usual neglect to give any guide cost as to your latest pet discovery while quoting 'firm' figures for those you don't approve of.

[snip the usual claptrap]

[Doctor Drivel]

He must be tired after walking around in his loafers. Sad isn't it.

That is what he said at the bottom. Sad isn't it.

[Phil Addison]

This is the salient point of my post - did you miss it?

"Try giving your comments in a more friendly and less aggressive way, and you might find they are more readily accepted."

[Remainder snipped unread. I stop reading your stuff once you start getting personal.]

Phil The uk.d-i-y FAQ is at

Google uk.d-i-y archive is at NOSPAM from address to email me

[Ed Sirett]

Thanks for all the replies. If/when I come to do an edit on this FAQ I may take a few of the suggestion on board.

On a certain point of fact. I do hold a G3 (unvented hot water storage) qualification, this may of course make me less inclined to see the down side of unvented cylinders relative to thermal stores and heat banks.

[Doctor Drivel]

Well piss off then.