Some Combi boiler questions

I'm thinking about replacing my back boiler with a combi boiler. The reasons are mainly about space.
The back boiler and associated gas fire take up a fair chunk of space in the lounge. The hot water tank takes up space which other people in the street have turned into a useful downstairs toilet. I do however have space in the utility room which I intend to site the new boiler.
I've read the combi-boiler section of the FAQ which was very helpful but I've still got a couple of questions.
1. How do I calculate the size of boiler I need? I've seen calculators for conventional boilers but they state that they are not for combis.
2. Can a new combi boiler be used with my existing radiators without too much trouble? I believe that my header tank will have to go but is it a relatively straight forward job apart from that? I don't intent to remove the back boiler straight away but just to disconnect the water and gas supply. As the job will involve ripping out a false chimney breast, I'll wait until the lounge is next due redecorating before taking it out.
3. I'm thinking of buying a boiler with a built in hot water storage tank. Any comments on this? Any recommendations on manufacturers or are there any makes to stay clear of?
4. I read somewhere on the net that from 2006, all new boilers in the UK will have to be condensing boilers. Is this true?
TIA,
--
Paul Giverin

British Jet Engine Website http://www.britjet.co.uk
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Paul Giverin wrote:

Unless you have massive heating requirements then you can usualy assume the heating side will be adequate, however you can go through exactly the same heat loss calcs as you would for a conventional boiler if you wish to work out the maximum energy input required for the heating.
In most cases you can simply select a model based on the hot water performance you require since that will dictate the overall power of the boiler far more directly than the heating load.

Usualy yes. You may have problems with leaks if the existing radiators are old, you may also find the need to replace some of the radiator valves if they begin to weep.
When I did ours, there were no dramas with the exiting rads or pipework inspite of it being reasonably old.

A google back on this group will get you plenty of recommendations.
The inbuilt tank versions vary from a very small tank used to preheat few litres of water to give an "instant" hot water output, to ones with a sizeable tank that are in some ways more like a conventional hot water cylinder system all built into a single box. What would be appropriate for you will depend on you usage and your expectations, also how good your cold water mains flow rate is.

No it's April 2005 IIRC. The actual requirement is that any boilers installed must be 86% efficient or better. This tends to preclude non condensers. There will be exceptions allowed to the rule in special circumstances, but unless you are looking for the cheapest boiler to install just before you move house then you may as well benefit from having the better efficiency offered by a condensing boiler.
--
Cheers,

John.

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Thanks John and Christian for addressing all my questions.
We don't intend moving house in the foreseeable future so I suppose I should look at condensing boilers. I did read somewhere that they had a shorter life than a combi boiler but I don't know how true that is.
Cheers,
--
Paul Giverin

British Jet Engine Website http://www.britjet.co.uk
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Paul Giverin wrote:

There is a fair amount of "urban myth" surrounding them. Some of the early UK designs were just adaptations of existing boilers and hence not well suited to the job. The materials used and the design tended to mean that they could suffer from bad corrosion. There is a secondary brush they got tarred with due to the extra complexity of their control systems intruducing more things to go wrong. So reliability compared to old simple bolers looked poor. To be fair however the ones of continetal origin (where the technology has been in use longer) did not suffer these problems as a result of already being on a later iteration of the design process.
If you step forward to today however, we are now on third and fourth generation designs, built with suitable materials (i.e. Ali, or SS heat exchangers). The contol systems of all boilers are now far more complex anyway so there is little difference to be found there between condensing and conventional. Again the reliability of the control systems have improved as well as a reult of ongoing refinement. The net result is a modern condenser should be no less reliable than a conventional boiler.
--
Cheers,

John.

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I'm not particularly enamoured of Aluminium heat exchangers in contact with corrosive condensate (even if some are claimed to have anticorrosion coatings - one scratch is all you need) but I have installed a number of condensing boilers with stainless steel heat exchangers and find no problem at all with them (yet<g>). Any problem may be initially viewed with abject horror by some but if you get your mind past the newfangled stuff mental block its all basic E&M engineering maintenance. The use of more and more LSI on the boards does result in less chance of fixing low electronic level faults and requires a throwaway renewal in many cases. Geoff at CET can help in a lot of cases (most?) but some of the more esoteric faults on new models may be things he has not met up to that point and so will not have an instant turnround. In these cases it is a case of buying a new board (manufacturers own supply EXPENSIVE!), I try to make sure Geoff gets the failed one to take a look at simply as an aid to him and as a possible future benefit. If you get a failure within twelve months Glow worm provide parts and labour free, twelve to twentyfour months you get parts free,pay for labour. After that you pay for all:-( Most things follow a bathtub curve on failures so unless you are very unlucky its not worth paying for breakdown insurance, no insurance company is in business for the public good)
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This is becoming increasingly true
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geoff

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Unless you live in a palace and don't like shutting the doors, any combi will provide enough heat for your radiators. They are sized by your hot water requirement. 28kW is fine for shower people, whilst those who like a daily bath would need as large as possible. Instantaneous combis are never going to be great for bath filling, but the shower performance can be excellent.

Almost certainly, unless you have an ancient "single pipe" layout. This would need replumbing to a "twin pipe" layout. Note that old radiators are not an efficient design. Modern radiators with fins give much greater heat output for the same size.

Yes. These can be better if you want more reasonable bath filling performance. However, they are a lot more expensive and can get quite large, which might be an issue if you are looking for a small wall hung model.

Basically, but it is irrelevent. You should fit a condensing boiler in any case, whether required to or not.
Christian.
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I'm sure that you've gone into all the pros and cons of switching to a combi boiler but I have to say that I wouldn't touch one with a barge-pole. I have a number of friends and relatives who have combis and not one of them would have one again if they could avoid it. Despite various different 'makes' they all seem to be unreliable, requiring frequent visits from c.h. plumbers to put right, and the flow of hot water is invariably abysmal - with frequent complaints of taking 30 minutes to fill a bath. By contrast my conventional wall mounted boiler feeding central heating and hot water has now been running reliably for almost 28 years with only the thermocouple requiring replacing once. I can also fill a bath in just a few minutes. It's up to you, but.................. !!!
Kev
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Well the existing back boiler is coming up to 20 years old so it may need replacing in the next 5 years or so. Having said that, its serviced annually and the bloke who services it says its in excellent nick.
I'm not a boiler expert (hence the questions) but from what I've been reading recently, it would seem that most problems occur with cheap boilers installed in new houses. I don't mind spending what it takes to get a good quality boiler which is large enough to give me a decent flow rate.
--
Paul Giverin

British Jet Engine Website http://www.britjet.co.uk
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"Paul Giverin" wrote | >> I'm thinking about replacing my back boiler with a combi boiler. | >> The reasons are mainly about space. | >I'm sure that you've gone into all the pros and cons of switching | >to a combi boiler but I have to say that I wouldn't touch one with | >a barge-pole.
One of their drawbacks is that you usually lose the back-up of an electric immersion heater.
| I don't mind spending what it takes to get a good quality boiler | which is large enough to give me a decent flow rate.
First thing is to check your cold water flow rate is adequate, usually measuring litres per minute with a bucket at the kitchen tap.
An alternative to a combi might be a wall-hung boiler and a mains pressure hot water cylinder (which does not need a tank) in the loft. Gets the cylinder out of the downstairs toilet space whilst giving you stored hot water. If the circumstances are right you might even get the boiler in the loft too.
Owain
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In an earlier contribution to this discussion,

A bit like automatic transmissions, perhaps?
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Cheers,
Set Square
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Set Square wrote:

Dunno. Can't say I've driven a combi boiler recently :-)
Brian
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In an earlier contribution to this discussion,

Don't worry, Kev will understand the significance!<g>
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Cheers,
Set Square
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Set Square wrote:

I sometimes seem to miss the hidden agendas on this NG!
Brian
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In an earlier contribution to this discussion,

OK, I suppose I'll have to spell it out!
In uk.rec.driving, Kev has been extolling the virtues of automatic transmissions - despite others saying that they are unreliable and lacking in performance.
And then - in uk.d-i-y (which I cross-posted here) - here he is warning people against combi boilers because they are unreliable and lacking in performance!
I just saw the funny side/irony of it all! OK, I'll get my coat.
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Cheers,
Set Square
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strung together this:

I think the back row are all with it now! Cheers for that. ;-)
--

SJW
Please reply to group or use 'usenet' in email subject
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Like boilers, not all autos are the same. And as regards performance whilst it's true a well driven manual will beat an auto, in give and take driving with the average driver, a *decent* auto wins every time.

Generalizations are always dodgy. See IMM's posts for proof.
However, I've yet to see a real world combi installation that matches the performance in terms of hot water flow of my storage system. Perhaps I need to get out more.
--
*If only you'd use your powers for good instead of evil.

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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BrianW wrote:

Don't panic, I'm sure you're not alone. A lot of people seem to miss the agendas that are in plain view.
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wrote:

Actually not a bit like automatic transmission. I would suggest that a modern auto is actually far more reliable than manual gearbox and clutch. Certainly in the car maintenance ng's you will find more postings about clutch problems than with auto box problems (possibly, I accept, because they out-number auto box by a considerable margin!). I have now owned four autos and never had any problems at all with the gearboxes.
Kev
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Uno Hoo! wrote:

And how do either of those compare to a Combi boiler in overall performance?
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