# Oil or Gas Central Heating for back boiler



## clicker (11 Apr 2010)

Hello all

I bought a house recently and it needs a whole new central heating system, i.e., boiler, radiators and pipes etc. I would like to get a multi-fuel stove that would heat the water (and some radiators) via a back boiler. I was told by a plumber that it is not possible to use a back boiler with gas central heating, it can only be done by using oil. I know little or nothing about central heating systems. Can anybody tell me if this is true?

I would appreciate any advice.


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## DGOBS (12 Apr 2010)

System waters from 2 heating sources should not be mixed, but as with many things people still do it.

Your plumber is correct, if you combine a back boiler and a modern condensing low water 
content gas boiler, you will quickly 'sludge' the heatexchanger leading to boiler failure 
(most heatexchangers in modern condensing boilers are cost prohibitive to replace) and
the manufacturer of the appliance will usually void the warranty because of the mixed 
heat sources.

While the practice is still not recommended for oil boilers, as the heatexchanger passageways in a oil boiler are large in comparison, and the boiler it'self acts as a heatsink it usually does not become an issue.


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## villa 1 (13 Apr 2010)

There is no problem interlinking an oil fired boiler to a solid fuel stove with an integrated boiler. The reason why many plumbers don't recommend this practice is because they simply cannot do the installation. System sealed installations are far easier to install with less stringent design requirements. An interlinked oil/solid fuel system will work perfectly if installed properly.


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## DavyJones (13 Apr 2010)

clicker said:


> Hello all
> 
> I bought a house recently and it needs a whole new central heating system, i.e., boiler, radiators and pipes etc. I would like to get a multi-fuel stove that would heat the water (and some radiators) via a back boiler. I was told by a plumber that it is not possible to use a back boiler with gas central heating, it can only be done by using oil. I know little or nothing about central heating systems. Can anybody tell me if this is true?
> 
> I would appreciate any advice.




This is a useful site. There are many ways of doing what you want.

http://www.boilerstoves.co.uk/linked-systems.html


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## DavyJones (13 Apr 2010)

DGOBS said:


> System waters from 2 heating sources should not be mixed, but as with many things people still do it.
> 
> Your plumber is correct, if you combine a back boiler and a modern condensing low water
> content gas boiler, you will quickly 'sludge' the heatexchanger leading to boiler failure
> ...



I am one of the many people who do.


If a system is designed correctly, I.E No pitching and the system water is treated, i don't see how sludging can occur. 

Heatsinking is not an issue on the heat exchanger in gas/oil boiler as hot water from the back boiler would never run through it. Again assuming it was designed and installed correctly.

I mainly follow manufacturer's instructions when fitting and i have yet to read that warrenty will be void if system water runs through another heat source, although it does commonly state, that warrenty will be void if system is not flushed and treated with inhibitor.


Dual systems are a very good idea and can be acheived in a number of ways. Either the conventional way or through system link, heat exchangers etc.

 The OP's installer did not advise correctly, you can even add a vented solid fuel back boiler/stove to you pressurised heating system, by way of a heat exchanger.


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## DGOBS (13 Apr 2010)

I can tell you 100% for sure, gas boiler manufacturers do not stand over boilers on mixed water systems, the fact the water does not pass though the boiler when not in operation is not in question (if plumbed correctly)

Go on any manufacturers gas boiler course, and they will tell you the same!
(I don't make the rules)

Also, as recommended by Oftec, even system waters between solid and oil 
should not be mixed.

Davy, do you mean as in using a dual coil heatexchanger? (as in system waters do not mix)


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## DavyJones (13 Apr 2010)

Interesting and news to me. Why would this not be stated in manufacturer's instructions? and how would sludge form?
Can you link me to OFTEC recommendations?

With regards to dual coil heatexchanger, we would fit these where a stove has been added to a non vented heating system. 


Ever since I became an installer I have fitted dual systems, Guys I trained under thought me so too did FAS when I was on block release.  I have been on many courses and it has never been mentioned, that is, having more than one heat source heating system water directly is bad. 

If what you say is true, I am sure it is an ass covering exercise by manufacturer's or they have seen a lot of badly designed/installed systems. I have seen a few.


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## DGOBS (13 Apr 2010)

In Ireland we have all seen more than a few, I am not disagreeing with you,
and maybe manufacturers are being over cautious, but again this is as I have
been instructed, that they should only meet through an indirect heat exchanger.

I assume the problem is related to the 'chance' under incorrectly installed conditions
that the gas boiler maybe subjected the temperature beyond what is deems 'in spec'
as in a lot of hi-eff gas boilers now use 'non metallic' materials in the outer shell, some
even embed thermal fuses that render the heat-exchanger void and has to be replaced

as for a link to this Oftec recommendation, as far as recall it is in book 4, and also in the oftec endorsed 'design heating guide'


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## gary71 (13 Apr 2010)

Gas boilers have never been designed (as far as i know) to work with a secondary heat source like a back boiler on the same circuit, they have never been tested or passed to work like this, in the UK which most instructions are taken from, installations of this type wouldn't be attempted, i never saw a back boiler on the same circuit as a boiler in the UK and as far as i am aware UK regs don't allow it, a twin coil cylinder would be the advised installation with UK regs, i have not seen any installations in Ireland with one of my boilers on the same circuit as a back boiler where it has not ended in tears and the back boiler being ripped out, that doesn't mean it can't be done, just boiler manufactures won't support it, if you fit a system link and it goes wrong then you would have to go back to system link as it's their installation instruction you are following and not the boiler manufactures, also with my boilers the warranty would be null and void which would have a impact on any insurance claims if there was a need to make any, Gary.


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## DavyJones (13 Apr 2010)

gary71 said:


> Gas boilers have never been designed (as far as i know) to work with a secondary heat source like a back boiler on the same circuit, they have never been tested or passed to work like this, in the UK which most instructions are taken from, installations of this type wouldn't be attempted, i never saw a back boiler on the same circuit as a boiler in the UK and as far as i am aware UK regs don't allow it, a twin coil cylinder would be the advised installation with UK regs, i have not seen any installations in Ireland with one of my boilers on the same circuit as a back boiler where it has not ended in tears and the back boiler being ripped out, that doesn't mean it can't be done, just boiler manufactures won't support it, if you fit a system link and it goes wrong then you would have to go back to system link as it's their installation instruction you are following and not the boiler manufactures, also with my boilers the warranty would be null and void which would have a impact on any insurance claims if there was a need to make any, Gary.



A twin coil cylinder is always used, Each heat source would have a direct and seperate primary circuit to cylinder, the secondary circuit is shared. One way valves ensure that any one applinace does not heat the other. 

Can you show me where it states this would invalidate warrenty on your boiler's installation instructions?


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## DGOBS (13 Apr 2010)

I think, the argument ensuing here is more about correctness of installation and best practice.

Most if not all manufacturers instructions would not state the 'how not to install their appliance' only the how to......and installation instructions only mentions the 'primary circuit' on the install, so the assumption as Gary (i think) was getting at, is the fact the
manufacturers does not give you install instruction for what you have done, it's a case 
of your on your own.

I suppose a good Irish gas boiler installation analogy would be the so called 'semi-sealed system', yes it works (not without pitfalls) but it is not as per installation instructions, so the manufacturer is within their rights to null and void the warranty,
all be it that the customer warranty would still lay with the installer at the installers cost.

Its all a case of can, could or should!


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## gary71 (13 Apr 2010)

The manufactures instruction give information on what the boiler is to be used for as far as the manufactures are concerned, they will also say that any relevant regs should be taken into account and list the regs.

If a heating system meets those regs or instructions then there is no problem, but if any installation is outside of the regs or instructions then it on the installer and his competence, if a boiler is fitted properly then there is less likely to be a problem because you won't see me, it's when the system doesn't work that problems occur, to date i have not seen one fitted in this manor that hasn't had issues, normally overheating or wiring faults. 

The manufactures instruction are a guideline and if the relevant information is not there then you would have to seek further advise, the advise for my boilers is that they have not been tested for this use, if you fitted a system link to their fitting instructions then you would be covered by them if any problems occurred.

Gas boilers(as far as i am aware) still have not been tested to work with a secondary heat source on the same circuit which can potentially generate more heat than the gas boiler leading to problems with latent heat or when the boiler trys to dump heat if it's running as well, if your installation is designed to prevent this and it works then the question of design isn't going to come up, but it still doesn't change that gas boilers have not been tested with this use in mind, Gary.


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## villa 1 (14 Apr 2010)

There are no definitive guidelines as to the installation of duel systems in this country. Most of the documentation is taken from manufacturers. A plumbing apprentice is or should be instructed on how to install a duel system during his apprenticeship. With the onset of high efficiency low water content system boilers this aspect of heating systems has declined but is starting to make a comeback due to the cost of oil/gas.
As Davy says the most common method is to use a duel coil heat exchanger with each heating appliance having a separate primary circuit. The solid fuel stove will have to have an open 1 inch(25mm) unrestricted gravity primary circuit. The space heating between the two appliances is then linked and check valves are fitted on both these circuits to stop those appliances heating each other.
I would not be looking to the UK for guidance on these matters as I have looked far and wide and cannot find very little information. 
Our apprenticeship system is far superior to that in the UK, once it is left in the hands of the people who are trained to deliver it properly. A person doing an OFTEC/GIS,GID course may not be qualified or capable of working on a wet heating system. 
I can see a resurgance in duel systems especially in rural areas that a not served by the gas network and I would advise the original poster to go for the dual system. There are many competant time served plumbing contractors well capable of installing an efficient safe dual heating system.


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## DavyJones (14 Apr 2010)

DGOBS said:


> I suppose a good Irish gas boiler installation analogy would be the so called 'semi-sealed system', yes it works (not without pitfalls) but it is not as per installation instructions, so the manufacturer is within their rights to null and void the warranty,
> all be it that the customer warranty would still lay with the installer at the installers cost.
> 
> Its all a case of can, could or should!



In the manufacturers instructions though, it does tell you how to connect boiler to mains, by way of filling loop or open vented by way of a F & E tank. (taking a baxi solo he as example). So as an installer I know that is how if should be done. If it is done any other way inc semi sealed way I would accept that 
the warrenty may well be null and void.

If however I design a dual system and am told it may void warrenty, I want to see where it says I can't do it. This country is full of these kind of systems, I doubt they are in breach of any regs or building codes (if done correctly).


Back when I was a kid these systems were all the rage, when I started plumbing we only ever pulled them out, now they are back with a bang (forgive the pun ), and as Villa has said, I was thought it as an apprentice, I and my lads teach our apprentices and so do FAS when they are away.


But I would love to get more information if anybody has it.


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## DGOBS (14 Apr 2010)

I would love to give you more, but all I can do is pass on what the manufacturers have told me! I don't design, test, or manufacture them so
all I can do is do as they say.

I am not disagreeing with you guy as to the correctness of what you are proposing (and Davy, was only using the filling loop as an analogy, albeit one
that causes me pain every day!) 

I also accept what Villa says about the quality of training of apprentices here,
alas most over the past 10 years or so seem to have forgotten it all, or so it
would seem when you go to any estate build of the last number of years!

Of course Oftec (101/105e/600a)/GIS/GID training would certainly not enable 
non-plumbers to install or work on the associated plumbing, how would it, as these are 'theory' based courses only (wondering why that has come into 
the conversation though!)

Love these conversations, every day is a learning day!


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## gary71 (15 Apr 2010)

DavyJones said:


> If it is done any other way inc semi sealed way I would accept that
> the warrenty may well be null and void.
> 
> If however I design a dual system and am told it may void warrenty, I want to see where it says I can't do it.


 
There is no difference in the two, the instructions are a guide on how the boilers should be used, if the boiler is fitted in any other way and it has a negative impact on the boiler either in performance, longevity or safety then that effects warranty, what the manufactures are saying is do it this way and you will have no problems because we have tested the boiler to do this, do it your own way then it down to your skill as a installer to fit the boiler correctly. There are lots of funky systems out there that are not covered by the fitting instruction that have no warranty issues because the systems has been designed properly.

I am not a boiler policeman and the issues of warranty only arise when the boiler is being effected by the system or controls, i am not going to say your design is the reason the fan went, but i am going to walk away if there is problems with over heating, circulation etc... 

The design of system you and Villa1 have mentioned wouldn't be a issue with me, unless there was a effect on the boiler(of course there wouldn't be), but the idea that Irish plumbers in general are the elite of the plumbing world is far from the truth of the installations i see on a daily basis, if i was to see a installation fitted to the standard you have mentioned i would be a happy chappy and appreciative of the installation. i see back boilers, stoves, washing machines... connected straight in to the same flow and return.

So long story short, warranty is only a issue when the boiler is being effected by the installation what ever the problem is, the instructions are only a guide and the buck has always stopped with the installer and fitting a stove is not the norm and would require a specialist installer with the skill set to do it safely and within local regs so as not to have warranty, insurance or explosive problems, Gary.


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## villa 1 (15 Apr 2010)

The irish (plumbing) apprenticeship training system is one the world's elite covering all aspects of industrial,commercial and domestic plumbing/heating installations. Have a look at the skill olympics and see how many medals and certificates of excellence are attained by our young crafts people.
The reason for all the shoddy domestic installatoins countrywide at the moment is the need for glutinous amounts of house/apartment builds. I have done research into apprentice on the job training and in many cases apprentices did get little, if any, on the job training from their qualified peers. This is the way apprenticeship is supposed to be geared. An apprentice learns his skills from a skilled craftsperson whilst on the job.

Many young apprentices were instructed to work on the own at too early a stage in their apprenticeship and in many cases were taught inaccurate skills from fellow slightly older apprentices. Even in the tiger days of construction sub contractors were put under enormous pressure to throw in systems because of low prices insisted on them by the builders/developers. Hence the employment of cheap labour - the apprentice.
There in no governing body/regulatory control of heating/plumbing installations (domestic) and this is the reason for the shoddy workmanship. A system of codes should be introduced like that in the US and this should be enforced strictly making sure that contractors are fully time served qualified craftspersons. This is unlikely to happen though as the house building industry here is rotten to the core.
It's time to straighten out the the industry!!
Thats my rant for today
By the way, getting back to the original poster, a stove is not difficult to fit into a heating system. Just make sure that it is open vented with the vent and cold feed brought into the system at it's neutral point.


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## gary71 (15 Apr 2010)

villa 1 said:


> getting back to the original poster, a stove is not difficult to fit into a heating system.


 
This is the bit i have a problem with when it comes to fitting a secondary heat source, it's easy for a competent installer because it's simple when you know how, but domestically in general the skills are not there, i can't comment on training for plumbers because i am not a plumber, i am a domestic gas heating specialist working for a manufacture covering the whole of Ireland, i fault find on a lot of gas boilers/installations, unvented cylinders and water heaters(and i am only as good as my last job). 

The domestic plumbers of Ireland have my heart broke, not wiring there own heating system and calling in electricians, no permanent live, auto fillers, not flushing, no inhibitor, not sizing gas supply, not sizing the boiler, not telling the customer what the filling loop is for or boiler controls, putting room stats over rads, near doors, over the toaster, plastic pipe that will melt fitted to unvented cylinders, capping the safety valves on cylinders, i could go on, with all these faults it me that gets the grief from the house holder and installer, so forgive me for my lack of faith when it comes to this type of work, i am more than happy to see installations fitted properly because i get shouted at less, Gary.


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## gary71 (15 Apr 2010)

To prove i was right all alongrolleyes i have found this: [broken link removed] 

but be aware that what i have written about boiler warranty's still stands and this is completely different from what i have seen, which is backboilers fitted straight on to the flow and return of a gas boiler blah blah blah... Gary


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## DavyJones (16 Apr 2010)

gary71 said:


> To prove i was right all along i have found this: [broken link removed]




That proves the opposite of what you were saying, you said it couldn't be done. There are loads of open vented condensing boilers. Handy leaflet though. Myself and Villa actually described that system exactly how it is shown. stick with the servicing 

Although I did learn an interesting thing yesterday, when a commercial job I was on was tested and turned on. A private contractor (Contracted by BGN) was on site to set and turn on meter. A very respected gas man with years of experiance. He informed me that it is indeed a very grey area and there are talks of including these systems in the regs. he basically said, you'll have to stand over it etc. very much like Gary and DGOBS have stated.


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## gary71 (16 Apr 2010)

DavyJones said:


> That proves the opposite of what you were saying.


I had a 10 hr round trip to Derry to put a analyzer in a boiler, so my sarcastic side came out




DavyJones said:


> you said it couldn't be done.


How could you doubt me



gary71 said:


> a twin coil cylinder would be the advised installation with UK regs.


 


gary71 said:


> that doesn't mean it can't be done, just boiler manufactures won't support it, .


 
To clarify i am talking about two types of installation, the correct way and the fruit loop way, i have only seen the correct way in books(i am not a plumber just a gas fitter), but i have seen the fruit loop way a few times and any posting about not being able to add the a back boiler/stove would be aimed at the fruit loops, you and Villa1 may not be aware of how many fruit loops are actually out there, i have seen thousands of installations and the fruit loops seem to out number competent installer 10/1, so i wouldn't be as confident as Villa in finding someone with the skill to install safely, Gary.


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## clicker (19 Apr 2010)

I have been offline for a few days and am surprised to see so many posts.  It will take me a while to read through them!  Thanks for all the comments/advice.

Clicker


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## magtape (20 Apr 2010)

Would'nt it be possible to use a stove that has temperature control and that can be pressurised. This would solve these problems.


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