Condensing boiler

[Mark Hennessy]

Thanks, David!

Interesting document, and clarifies a point that I found was surprisingly hard to be sure about: the 2.5 metre distance is when facing the boundary.

My flue is quite close to the party wall - it's in an upstairs bedroom at the rear of the house, and the flue points down the garden. See position C in the document - only it's upstairs. Relative to opening windows, it's more than far enough away from openings...

If I'd put it on a side wall at the rear, then we would be in trouble because the passageway down the side of the rear extension is only 2 metres wide. Here, the flue would have been pointing sideways. That said, the neighbours house is a mirror image, so there would have been 4 metres between the structures, so technically there would have been no risk of condensation forming on the neighbouring property.

When we first moved in, our neighbour complained (amongst other things) about the flue position - despite the fact it was decided some 8 years previously by a previous but one owner. In the intervening years, she's been completely unreasonable with us about absolutely everything, so I felt under no compunction to move the flue to the roof or similar - and as the current position meets the regs, I've left it where it is. Had she been nicer, I would have moved it as a courtesy. Of course, there's no point trying to explain this to her...

Meanwhile, at the front of the house, the other neighbours have a boiler flue even closer to us as their boiler is installed on the party wall in the upstairs front bedroom (which is actually a kitchen because the house has been divided into flats). The flue is within inches of the boundary, but faces forwards again, so no problem...

Actually, our new boiler hardly "plumes" compared to the old one because it's running with a much lower return temperature, meaning that much more water vapour is being extracted by the condensation process. Another reason to consider Weather Compensation! Another neighbour, with a smaller house, has a boiler that looks like a steam locomotive - I dread to think how that system is working!

Cheers,

Mark

[Coherers]

Interesting document, and clarifies a point that I found was surprisingly hard to be sure about: the 2.5 metre distance is when facing the boundary.

I believe the 2.5 metre measurement is relevant to the assessment, not to the installation that comes later. This is one of the additional requirements described as being "for the purposes of the Condensing Boiler Installation Assessment Procedure ONLY, more stringent requirements apply ... to reduce the possibility of nuisance to neighbouring buildings. "

However, the actual siting is allowed to have "regard for householder preference"

The legal requirement is 600mm - see p 50 of the Approved Document J. (http://www.planningportal.gov.uk/uploads/br/AD_J_wm.pdf) - I think this comes from BS 5440

No doubt, the BCO might try to insist on the "more stringent" requirements, but as far as I can see they wouldn't have a legal leg to stand on. ( Not that that would stop them!)

Jeremy

[Mark Hennessy]

I've seen that before elsewhere, but hadn't made any effort to commit it to memory because it doesn't cover my situation. I have a flue pointing away from the house, down the garden, on the rear wall of the house, but it is quite near to the boundary. As far as I can tell, there is no obvious recommendation or regulation to say how close to the boundary my flue would be allowed. Of course, if it was pointing at the neighbours, that would be different. Everyone I spoke to at the same concurred; and agreed that as it wasn't specifically mentioned, it's not a concern. That was OK with me - given that (a) on the front of the house the other neighbours have an outward-pointing flue that is even closer to the boundary than mine, and (b) if it came to it I wouldn't be too upset about retrofitting a plume management kit, I decided to stop worrying about it

All the best,

Mark

[Coherers]

Technically, I think that would be covered by the location H restrictions:
"From an internal or external corner, or to a boundary alongside the terminal (2) " (my emphasis; see diagram on page 49)

For a balanced fanned flue, that minimum distance is 300 mm. However, for both this diistance, and for the opposing boundary measurement, the distance can be less if the applicance has been "shown to operate safely" at that distance.

All in all, you are right not to worry - if you watch how most professional Gas Safe-registered engineers ignore their **legal** obligations with respect to working on open gas ways, a possible, theoretical non- compliance with an obscure clause buried in the approved documents is not even worth giving a second thought to.

Jeremy

[Radio Fixer]

Very interesting Mark. I knew nothing about the Weather Compensation technique. On sealed systems a thing that happens to some is that it wont hold pressure after the new installation. This happened to my neighbour with his 70's house and was put down to the downstairs pipes being in the concrete floor screed. Back then the pipes were not covered and apparently the lime etc causes micro leaks, not enough to allow water to escape, but they wont hold pressure. So he had to have all new pipe work, done as a drop system from the upstairs floor. Certainly something to be taken into account if having such a system... ups the cost considerably.

On power flushing I didnt do this when I upgraded the system last year. I fitted all new rads and flushed the pipe work with suitable couplings and a hose, plenty of mains pressure here. At this time I replaced the HW cylinder and put in new primary pipework to it. This is gravity feed and I know its old fashioned but its so beautifully simple and I dont have a motorised valve anywhere (they fail eventually). I do have of course a wireless tank (boiler) thermo and a room one (pump). The cylinder is vertically above the boiler and it works very well now. I was amazed how coked up the old pipe work was, just a small hole down the centre of it. No wonder gravity wouldnt circulate thru it.

I wonder if the header tank and drawing in oxygen is a bit of sales pitch? Since the upgrade with a good refill of anti-corrosion mix the system is completely quite, never seems to need bleeding and everthing works fantastci. Did put the best (expensive!) rad valves on all the upstairs ones and one giant rad in the hall. These as far as I can tell just work... in the summer screw them closed and now set as required.

cheers Gary

[Yorkie]

I don't wish to sound like a 'jobsworth' but in commisioning or servicing a condensing boiler (or any other boiler for that matter, the Gas Safe Register (formerly 'CORGI') announced in 2010 that all registered gas engineers who have modules CEN1 now require the combustion analyser ( different name for a flue gas analyser) qualification 'CPA1'. Those central heating engineers who do not hold the CPA1 qualification after 1st April 2012 will have their CEN1 suspended. In other words, if not CPA1 qualified within the next two months, (having had two years to come up to speed), they can still retain their Gas Safe registration, but will no longer be permitted to work on central heating boilers. (ACS stands for Accredited Certification Scheme and CEN1 is the specific diploma required for boiler engineers).

British Standards such as BS 6798, BS 7967 and BS 5871 Part 1 state the requirement to use a flue gas analyser when maintaining and servicing particular heating appliances. The CPA1 Combustion Performance Analysis of Domestic Appliances assessment is intended to provide 'gas engineers' with the essential knowledge of correctly using a flue gas analyser for boiler repairs. Monitoring the products of combustion is intended to ensure that a heating professional has the ability to precisely control levels of carbon monoxide (CO), oxygen (O2), the ratio of carbon monoxide and carbon dioxide (CO/CO2), excess air and flue gas temperature.

At the risk of sounding cynical, I dare say that there are so-called 'heating professionals' who can't even spell 'combustion analyser' let alone know how to use one. Whether the traning module will add to their fund of knowledge, only time will tell.

At the rate things are going, in the not too distant future it will be mandatory to hold qualifications in colonic irrigation!

Given that older balanced flue boilers don't have a flue gas analysis point, and can only be checked by access to the flue terminal, I'm not sure to what extent the new requirement will be complied with, when some boilers are in lofts or in other locations high above ground level, with no access to the terminal other than via ladders or scaffolding.

Modern condensing boilers have a sampling point at the boiler which obviates the need to sample at the flue terminal. A jolly handy feature in Ed's case, given his intention to have a 9 M high concentric flue!

Wittered David.

[Mark Hennessy]

That's very interesting, and I admit that I didn't know about any of that. Thanks as usual, David

Interestingly, my boiler controls the fuel-air mixture by measuring the ionisation current. I wonder why this isn't more widespread - after all, all boilers have the electrode in place to sense the basic presence or otherwise of the flame, and it isn't that complicated to extend that binary function into an analogue value back to the flame controller...

Also, this boiler has an NTC thermistor to measure the flue gas temperature. I wonder why? I guess it's a safety feature at the very least - after all the flue is all plastic - but I wonder if it plays a part in determining some operating parameter of the boiler? I guess the flue temperature gives the boiler some indication of the heat transfer into the heat exchanger? I know that there is another NTC measuring the flow temperature at the exit of the heat exchanger, and a bi-metallic switch in the same location which I presume acts as a safety device in the event of the controller getting confused. As far as I can see, it doesn't appear to measure the return temperature.

So, is the flue gas temperature sensor common in modern boilers?

Needless to say, I have a carbon monoxide alarm in the same room. Given their low cost, I wonder why they aren't an integral part of the boiler? Perhaps they will be before much longer - things are always changing...

Talking of which (and forgive me if I said this before), the friendly chap at Viessmann tech-support told me that variable-speed water pumps will become mandatory in a couple of years time. I don't know if he knew this as a fact, or was speculating, but interesting none-the-less. I considered the option because I liked the idea (one more variable that can be controlled to avoid cycling and increase efficiency), but he talked me out of it in the end. It added ~£300 to the list price, and while it saved around 40 watts IIRC, he didn't think it would pay in the long run. I think they use DC brushless motors, which are becoming commonplace in washing machines and other white goods, it seems.

Mark

[Mark Hennessy]

Hi Jeremy,

Technically, I think that would be covered by the location H restrictions:
"From an internal or external corner, or to a boundary alongside the terminal (2) " (my emphasis; see diagram on page 49)

Again, this doesn't quite cover it as far as I can see; there is no corner because this flue is in an upstairs bedroom, nearly 20 feet from the ground. It's at the back, and it's a Victorian terrace where each neighbour is the mirror image of the other - so imagine a 20 foot wide structure protruding from the rear of the "main" terrace; we have one half, and the neighbour has the other. If the boiler was downstairs in the kitchen, then there would be a wall and fence forming a corner on our boundary. Here, up in the air, the boundary is "virtual"

All in all, you are right not to worry - if you watch how most professional Gas Safe-registered engineers ignore their **legal** obligations with respect to working on open gas ways, a possible, theoretical non- compliance with an obscure clause buried in the approved documents is not even worth giving a second thought to.

Yes, completely agree on every count

Thanks,

Mark

[Mark Hennessy]

Hi Gary,

I was amazed how coked up the old pipe work was, just a small hole down the centre of it. No wonder gravity wouldnt circulate thru it.

Wow!

I wonder if the header tank and drawing in oxygen is a bit of sales pitch?

Admittedly, it was a British Gas engineer that last tried to convince me of this. I arrived at my mothers house to find him replacing a pump and insisting she get a £700 powerflush, and a Magnaclean filter. I asked how come sludge was able to form if BG service the system annually, and was met with a lot of bluster about how it's impossible to maintain inhibitor in a non-sealed system... Of course, in general, BG don't seem to actually service anything; they appear to perform the most perfunctory of safety tests with a flue gas analyser, and nothing else if this is OK. But had they checked the strength of the inhibitor, they wouldn't be able to force the power-flushes on unsuspecting customers. I'm with Jeff Howell on this one* - I simply can't understand why people continue to give this company their money.

* I seem to agree with a lot of what he says. I promise I'm not on commission

All the best,

Mark

[Coherers]

At the risk of sounding cynical, I dare say that there are so-called 'heating professionals' who can't even spell 'combustion analyser' let alone know how to use one. Whether the traning module will add to their fund of knowledge, only time will tell.

At the rate things are going, in the not too distant future it will be mandatory to hold qualifications in colonic irrigation!

Agreed. Unfortunately, left to themselves, regulators have a strong vested interest to keep increasing both the remit and the depth of their regulations in order to justify their existence. And in this space they can always use the trump card of "safety". In this respect, CORGI wasn't too bad as it had the interests of its members to think about (which was actually the reason it lost the regulatory-type function). Now the Gas Safe Register is standalone and has a "Chief Executive" and the full panoply of corporate infrastructure, they have to keep adding requirements if they are to grow their little "empire" and further their careers.

The problem is, increased regulation doesn't automatically result in increased safety - what tends to happen is that as the rules get more complex, and harder to comply with, more tradesmen start to ignore them. And not just the silly regs, too much regulation makes it more likely that people will start to ignore the lot. Furthermore, more cowboys move in to undercut those who do work to code as householders regard the legitimate tradesmen as extortionately expensive.

The secret of good regulation is making sure it is pragmatic and appropriate to those who have to comply. And a lot of what we see now isn't either.

Jeremy