Condensing boiler

[Ed_Dinning]

Hi Folks, following on from my earlier thread on insulation of a free standing boiler.

I've seen a lot of articles about gas saving, carbon footprint etc as well as a lot of negative comments and people who have "lost " money on the deal due to very extended payback periods; together with the "if its working OK don't change it" advice.

Some thoughts please on the following situation:

I have a 30 year old Gloworm 65-80 floorstanding gas boiler with comventional flue. It does emit some kettling noises but it will be flushed/ de-scaled in the summer.
It is connected to a well insulated cylinder and is a fully pumped, but open vent system with 4 zone valves that close the whole system down when all zones are satisfied.
In the summer months an immersion heater is used for hot water with the boiler turned off (say 8 to 12 weeks max), running about 1 hour/ day or less.
I intend to add a solar coil at the bottom of the cylinder, run from a 1M sq solar panel of home design.
I have a 5 bed detached house; 600ft ASL, well insulated and generally protected from the worst of the prevailing winds by the other houses in the row.
Typicial gas cost are £1200 pa.


I had thought of replacing the boiler with a modern condensing unit (not combi) and retaining the rest of the system.
I believe the new boiler would be a balanced flue type that would be fitted into the existing vertical chimney of about 9m length, with no bends. The utility/boiler room should not then need full air ventilation and I have access to an internal condensate drain.
I intend doing the work myself, with flue and gas connections by a friend who is a registered installer.

Can anyone recommend suitable boilers makers/ models[/size][/font] and an indication of cost, plus some ideas on reliability?

Thanks, Ed

[Radio Fixer]

I used to have a 30 year old boiler similar to yours Ed and went along with it... well it worked fine and it was all good old solid cast iron. But one night the gas valve jammed and didnt shut off when the power from the time clock went off!! So the gas just went roaring thru and eventually we were woken by the heat and sound of boiling water etc. So the boiler got turned off for ever as no valves were available and it was time for it to go anyway. Just imagine what would have happened if we had been away.

According to the plumber, who put in the new one (not condensing), the bottom melts out of the header tank and then the ball cock drops and cold water pours continously through the house.

This story may inspire you to get on with the replacement...

Condensing boilers had a lot of bad press for reliabilty but hopefull they are better now. We just squezzed in before the current regs and were able to have another floor standing job, with conventional flue, in the original boiler cupboard. This suited me as we have no where to hang a balanced flue job on an outside wall. I think its pretty efficient... no pilot light etc.

cheers Gary

[Coherers]

Worcester Bosch have a pretty good name for reliability - which given the cost of repair is a critical factor.
IIRC, I have also heard people say Vaillant were pretty reliable too - although I can't swear that was in the specific context of gas condensing applicances. Viessmann is another name that comes up.

This is a common topic on the DIY / trade forums - there is a fairly recent discussion by others here

However, bear in mind that installation engineers favour boilers that are easy to install (=profitable) rather than "good" in the sense we might understand it !!

[Yorkie]

A few points that might help Ed:

At best, your Glow Worm boiler will be 55-65% efficient, made worse by the fact that it has a permanent pilot, which is rather like having a 24/7 gas leak, except that the gas is alight in the boiler! It is so innefficient that it would have instantly qualified for the £400 government grant when it was in being.

Your boiler being a '65-80' means that it was 'range rated' which - by varying the gas burner pressure - could have the heat output varied from 65,000 BTUs to 80,000 BTUs. Nowadays, boiler heat outputs are quoted in KW/H. A KW/H is equal to 3,412 BTUs, so for example, a 25KW/H boiler will equate to 25 x 3,412 = 85,300 BTUs.

A condensing boiler will have a rated efficiency of 90%+, in Band A of the SEDBUK rating. You can check the effeciency ratings of a whole range of current production boilers at the SEDBUK site. (SEDBUK is th national standard for all domestic heating boilers in the UK, whatever the fuel source, and is an acronym for 'Seasonal Efficency Of Domestic Boilers in the UK'. (Current boilers are all very similar in efficiency).

You ask about fuel savings. The SEDBUK site has an annual fuel saving cost calculator where you can input your present gas consumption figures and see what savings you would make with a condensing boiler.

There's lots more information at the SEBUK site, which is here:

http://www.sedbuk.com/

It's almost impossible to make meaningful assessments of fuel savings from one year to the next - you can only compare an inefficent boiler with the consumption of a fuel-effecient boiler to genenrate the same amount of heat. The amount that your boiler actually consumes over a heating season from one year to the next is highly sensitive to outside temperatures, which is calculated historically on what's known as 'degree days'.

The temperature at which you set your room thermostat, and the number of hours per day your programmer is set to also has an enormous bearing on consumption. My house has double glazing, cavity wall insulation, and 300mm of roof insulation. Let's assume that with the heating off, my house has an indoor temerature of 10 C. If I set the room thermostat to 20C, that's a temperature rise of 10C. But 20C far to chilly for my old bones, so I have it set at 23C - nice and toasty! But that increases the consumption by 15%, so if saving money was a high priority, I'd put a pullover on and turn the room thermostat down, but comfort ranks higher than cost with me, so 23C it is!

As to how you go about replacing your boiler with a condensing one, assuming that you wish to comply with non-statutory and statutory guidance and requirements, there is a 'Guide to Condensing Boiler Assesment Procedure' which sets out the criteria for the siting of boilers, flues, and so on.

Though there are non-condensing boilers on the market, they're not simply a matter of personal choice, (whether down to financial or practial considerations). To comply with codes of practice - as any reputable installer would do - a non-condensing 'high efficiency' boiler (deemed to have an efficeincy of >72%) should only be installed where it impracticable to fit a condensing boiler, which is only going to be in exceptional circumstances. The Guide sets out the critieria in which a non-condensing boiler will satisfy the requirments of a Building Control Officer. (Not relevant in your case Ed as you've decided on a condensing boiler anyway).

You mention that you believe that the boiler will be a balanced flue one, and that's correct. All boilers nowadays must be balanced flue (except fire/back boilers, which are frowned upon except as replacements). From what you say, your present boiler is a conventional open flued boiler which takes its combustion air from within the room in which it is sited, and discharges the products of combustion up a flue (lined chimney?).

Older balanced flue boilers had to be sited on an outside wall as the flue box bolted onto the back of the boiler. A modern balanced flue condensing boiler flue is fan-assisted, and has two concentric flue pies - the outer one drawing in the combustion air - the inner one discharging the products of combustion ('fumes') which consist of water vapour and carbon dioxide. Condesing boilers have a lot of flexibilty in their flueing arrangments, in that you can have quite long horizontal and vertical runs, and 90 degree bends (a 90 degree bend being equivalent to 1.3M length of flue when calculating the flue length).

I haven't looked at individual makers' technical data, but to my mind, a vertical concentric fan assited flue length of 9M sounds a bit bizarre. All that your existing flue has to do is to work as a chimney, but a condensing boiler fan would have to draw the combustion air down 9 metres of concentric flue pipe, and shove the products of combustion back up another 9 Metres into the atmosphere. Are you quite sure that there's no other way of running a horizontal flue from the top of the boiler to an outside wall, provided that the flue terminal positions complies with the criteria set out is the assesment guide? (A 'horizontal' flue should actually have a slight slope towads the boiler for any condensate that forms in the flue to drain back into the boiler).

As to reliabilty, in the early days of condensing boilers (which have been around for 20 years or so), some got a bad reputation for heat exchanger failure, but modern ones have stainless steel heat exchangers, which in part, helps bump up the cost.

Most problems these days - particualrly last winter - have been down to poor installation of condensate drains, often with blatant disregard for makers' instructions, with long runs of exposed condensate drains prone to freezing. You've said that the condensate drain isn't an issue in your case Ed. An indication of reliaiblty can be assumed from Worcester Bosch who give a two-year warranty and Baxi, five years. Worcester Bosch have a good record of relibilty, and excellent service back-up and installer training facilities. Our Worcester Bosch 'Greenstar Ri' (25kW) has been in for two years now, and has never skipped a beat.

Finally, on the 'solar coil' you intend to fit in the cylinder, presumably there is some thermostatic arrangement whereby if the water temerature in the cylinder is higher than that from the solar panel, a thermostatic valve closes the circulation off from the panel, otherwise it would send lukewarm water down to the cylinder, and hot water out of the cylinder back to the panel to heat up the atmosphere - a sort of 'district heating scheme'!

Hope these lengthy notes are of use for reference Ed. (Safety Warning: May induce drowsiness - don't read whilst operating machinery!).


David

[pwdrive]

Hello Ed, I would echo Davids thoughts on a 9 meter vertical flu, it seems like a lot of push and pull for exhuast fumes and combustion air, not to mention any poss down draught down the exhaust pipe (inner) that can be caused by the wind. I put in an oil boiler in the old place about five years ago, that was balanced flue, it came up from the top of the boiler for about 800mm then straight out through the wall to the outside air, the wall was 2ft thick granite which was a pain to drill out but the end result was that I could check the balanced flue terminal without having to climb any ladders, if the flue terminal ever gets blocked it can be very dangerous. Good luck whichever way.

Lawrence.

[Ed_Dinning]

Hi Folks, trhanks for the replies so far, keep the ideas coming. I won't be replying for a few weeks as I will be away but managing to read the mails.
Present boiler is on an interior wall uner a lined flue from original oil boiler. Looking at literature it appears that vertical flues up to 10M are allowable (at cost) for some boilers. Horizontal flue in cieling space to outside wall (3M) would be a pain and would discharge into a narrow alleyway between houses, but probably clear of opening windows.

Gary, not so far had any gas valve problems, but replaced a few thermocouples. Gas valves are usually bought in by boiler makewrs (Honeywell?) and are meant to fail to safety. (the faulty ones I've heard about have all done this).
My gas valve is electric with an boiler waterjacket stat that removes the LV power to the coil.

Present flue terminal on chimney has never presented any problems and it is convection, not blown. If a blown flue is blocked it is presumably fail safe?

Solar system will be a coil in the very base of the cylinder. Heat collector will be on porch roof at first floor level and same level as cylinder. System will be pumped and contain a glycol mixture with a small header tank in the loft. Control will be via several "LM" type sensors at various points in the system. I may also need to look at a "dump" sytem in case of overheating in summer.

The Gloworm sounds promising if they give a 5 year warranty, but I need to do a lot more work before deciding.

A further question, what is you opinion on boiler and system flushing equipment and methods?
Bear in mind that whatever happens the system will be opened up this summer. Cylinder will be removed (and opened) to fit solar coil.
Pipework will be open as I will be tidying up and re-positioning the manifold and motorised valves. It would even be quite easy to take the boiler right outside to flush it.
System has been run with inhibitor since new, some trace of black gunge when a radiator has been removed and some kettling in boiler now, but no real gas/air in system problems (one particular red will need bleeding every 4 months)

Thanks, Ed
Ed

[Yorkie]

A further question, what is you opinion on boiler and system flushing equipment and methods?
Bear in mind that whatever happens the system will be opened up this summer. Cylinder will be removed (and opened) to fit solar coil.
Pipework will be open as I will be tidying up and re-positioning the manifold and motorised valves. It would even be quite easy to take the boiler right outside to flush it.
System has been run with inhibitor since new, some trace of black gunge when a radiator has been removed and some kettling in boiler now, but no real gas/air in system problems (one particular red will need bleeding every 4 months)

Thanks, Ed
Ed

When a new boiler is fitted, ordinarily, it's a requirement to 'powerflush' the system. The equipment consists of a powerful pump which pumps clean water through the system and drains off the sludge that may have collected in the radiators over the years. Obviously it's not good practice to fit a new boiler onto a sludged up system.

That said, 'powerflushing' has gained a bad name, and not without some justification, as it's often used as a 'make-work' moneyspinner (not least by certain large outfits who will remain nameless), with gullible customers who are told, and believe, that they should have their system powerflushed to make it more efficient, even though there are no signs of problems, such as some or all radiators not getting hot when the circulating pipework is.

In your case Ed, since the system will be drained down anyway, if you want to do a thorough job, although it would be a bit of a pain, you'd be just as well to remove each radaitor, take it outside and flush it through with a hose. Turn the radiator upside down, fill it with water, then turn it upright to let all the gunge drain out. If you do that a couple of times with each radiator, they should come nice and clean.

On the face of things, pressed steel radiators mght see the worst material for containing water - they'll rust won't they? No they won't, and no they don't! When a system is filled with fresh water it contains oxygen, but this is soon dissipated and in so doing, will leave a film of oxide (rust on the inside of the radiator, and that's it. Once the oxygen has done its worst, there will be no more in the system unless and until it is drained off again. That said, it makes sense to apply rust inhibitor to the system each time it's filled. Most systems do have minute leaks which go unnoticed - at radiator valve glands for example. Ths is why on presurised systems (which only operate at about 1.5 Bar - 21PSI) often lose pressure over time, and need re-pressurising by opening a valve on a neaer the boiler, observing the pressure gauge on the boiler util its is the correct pressure - a simple taks for householders to perform, and another lucrative money-spinner for those who have a combi boier and find that it's shut down. Along comes the 'service engineer' and does what the customer could have done. £35 for five minutes work - easy life!

If people are in the habit of removing radiators to decorate behind them or have alterations to the system which call for it to be drained down, that introduces fresh oxgenated water, so they system should be treated once more with inhibitor.

When you've done the work Ed, fill up the system without inhibitor, and bleed the radiators. Check for leaks, then open all the radiator vents and drain the statem down to flush it. It you're conscientious, allow the system to come up to temperature, and after running it for an hour or so, drain it down again to rid it of any flux or grease which the hot water will have melted. Then fill up and put inhibitor in as directed in the instructions. (You want it in the system itself - not in the expansion tank, so it needs to go into the tank before the system is full).

As to saying that 'one radaitor will need bleeding from time to time' often it isn't air in ther system, but hydorgen from hydrolysis of the water. You can easily check that by holding a cigarette lighter to the 'air' to see if it ignites. If so, it's hydrogen of course. You can get automatic bleed valves which are very cheap simple devices. Basically, they have a little plug inside which - if it dries out will shrink and allows air to bleed from the system, then as soon as water comes into contact with the plug, it swells and stays swollen till more air/hydrogen makes it shrink again. Neat eh? You might find that when you've fully drained and flushed the system and filled up including inhibitor, that the problem goes away.

Hope these additional pointers are of interest and help Ed.

Best of luck in your endeavours!

[Mark Hennessy]

Hi Ed,

Having just re-read the previous thread, a lot of good advice has already been given there. In summary, I'd say the following:

I've just fitted a Viessmann. A very easy DIY job (apart from the gas, obviously). I went for the Vitodens 200 System Boiler - unless you're very short for space, I wouldn't recommend the 100 as that is a "dumbed down" model for the UK market - it had some reliability issues initially as well (long since solved, but you'll find no shortage of people complaining in the forums - just check the dates of the posts, and don't let them put you off the brand).

The system boiler contains the pump and diverter valve, so has 4 pipes; 2 for heating flow/return and 2 for water flow/return. You can keep your existing diverter valves and use the boiler in 2-pipe mode if you wish, but you would be mad to do so (explained later).

Most condensing boilers on the market still use aluminium heat exchangers. This is bad! See my previous posts.

You might have trouble with the flue. There are new regulations that state the flue has to be accessible for inspection at all points where there are joins. This will mean adding hatches or similar in the chimney stack. Not good. Have a look at Jeff Howell's column on the Telegraph website, where this has been discussed previously. I'd find a way to run it horizontally if humanly possible. Don't forget that actually it needs to slope down slightly back to the boiler...

I've also read somewhere that boiler cupboards do need ventilation, even when the boiler is room-sealed. I haven't had a chance to investigate this fully yet - apparently it's a new regulation - but if true, it's a real pain. Ventilating to the outside will surely bring in enough cold air to undermine the overall efficiency of the installation. Certainly, manufactures state that ventilation is not required, but regs override manufacturers guidelines here... I would welcome clarification on this if anyone knows any more...

While on the subject of efficiency, I wouldn't worry about the published figures on the SEBUK site. What's the difference between 90 and 91% when you're coming from 55-60%? Instead, it's far better to focus on the TCO, which means avoiding boilers that will break down and wipe away any savings on your gas bill. Also, these figures don't include the potential savings from Weather Compensation.

Weather Compensation: I have it, and I am still really, really impressed by it. IMHO, you would be mad to ignore it. Not only does it improve the comfort, it also saves on the bills. I couldn't work out how it would even begin to work, and really, I went out on a limb, based on advice from a trusted friend. But, to say I'm very pleased would be a massive understatement.

There is no room thermostat. The boiler adjusts the flow temperature based on the outside temperature. It does all it can to maintain a constant indoor temperature in the face of varying outside temperatures, while avoiding cycling. It's very smart. If the boiler has just spend 10 minutes heating the water (DHW priority), it uses an increased flow temperature for the heating for a short period, just to compensate for that short period of cooling. There is definitely an element of "fuzzy logic" or similar, but whatever it is, it works well.

Weather Compensation is mandatory in some parts of Europe. Viessmann have been doing this for years, and know what they are doing. Worcester-Bosch have only just started, and they are playing catch-up. And they still use aluminium for the heat exchangers. Although I have a lot of Bosch tools and white goods, I wouldn't choose one of their boilers.

WC maintains comfort by running the boiler continuously, but at a very low flow temperature. This alone saves a lot of fuel, and is frequently advocated by Jeff Howell (his correspondents either tell him he's mad, or tell him that it makes an amazing difference to the bills - clearly the former group haven't tried it!). Because the boiler can modulate down to a quarter of its rated output, it means that in temperate weather, it runs at low power rather than cycling on and off. The radiators aren't dangerously hot, and the fabric of the house is kept drier - especially important for old houses.

DHW priority is essential - the boiler can't run at two temperatures. When heating water, it ramps up to 70C or so. When heating, the WC decided the best flow temperature. That's why you'd be mad to use it in 2-pipe mode. If so, you'd have to choose a flow temperature hot enough to heat the water, which would be too hot for heating - causing cycling.

The Vitodens 200 supports zoning and solar. I haven't needed to investigate these options, but I'd recommend you downloaded the guide and had a good look. The control system is very advanced (yet very user-friendly) and will almost certainly do a better job of zoning than any 3rd party or (with the greatest of respect) DIY solution. Our house is too small to zone, plus as it's a Victorian terrace with solid walls I'd prefer to keep it warm and dry throughout anyway - but I am interested in solar for the hot water. I'd buy a new cylinder with the extra coil - how do you propose adding another coil to yours? Can you cut them open and solder them back together? These things have a finite life anyway - in fact I was fearing the worst when attempting to replace the pipes going to the coil, but so-far so good!

You should consider changing to a sealed system - I think that many manufacturers expect/mandate that these days. The trouble with a header tank is that it lets in oxygen. The expansion vessel is normally built into the boiler - normally behind everything else so that when the diaphragm fails, most people simply fit an external one!

In terms of warranty, the Viessmann comes with 3 years if you (or a regular contractor) fits it, and 5 years if it's fitted by someone who has attended the training - which I believe is free, or very cheap. The stainless steel heat exchanger is guaranteed for 10 years. Looking very, very critically at mine, I couldn't see a single component that would be difficult to replace it the need arises. The expansion vessel is at the side, and comes out after undoing 2 screws.

The boiler wasn't even expensive. Obviously a bit more than a Worcester-Bosch, but well worth it. Investigate PTS, who have branches in many towns and cities. You can download their prices, and you'll find that they give you around 50% off without even asking.

One day I'll start a thread detailing my installation with some pictures, etc, but I hope this gives you something to think about in the meantime...

Mark

[Coherers]

Horizontal flue ... to outside wall (3M) would be a pain and would discharge into a narrow alleyway between houses, but probably clear of opening windows.

My neighbour had a boiler installed a few years ago, with the flue discharging into the quite wide side passage between houses. Although the flue was installed according to the relevant British Standard (BS 5440?) / manufacturer recommendations etc, we frequently get the fragrance of "combustion products" in the second-floor bathroom coming in via the window. This has been a sore point ever since. What we wanted the neighbour / installer to do was to extend the flue up the wall to discharge the vapour plume above the windows. However, to no avail. Litigation has been considered!
Pity I don't have you as a neighbour, Ed !

Jeremy

[Yorkie]

My neighbour had a boiler installed a few years ago, with the flue discharging into the quite wide side passage between houses. Although the flue was installed according to the relevant British Standard (BS 5440?) / manufacturer recommendations etc, we frequently get the fragrance of "combustion products" in the second-floor bathroom coming in via the window. This has been a sore point ever since. What we wanted the neighbour / installer to do was to extend the flue up the wall to discharge the vapour plume above the windows. However, to no avail. Litigation has been considered!
Pity I don't have you as a neighbour, Ed !

Jeremy

In post #4 above I banged on about the official government guide to the Assessment of Boiler positions, which came into being in 2005. It's very detailed and is what planning control officers rely upon, but I forgot to give the link to the guide, which is here: http://www.idhee.org.uk/ExceptionsGuide.pdf

It covers such matters as flue terminal siting, with sketches of what is and what isn’t permissible. (See page 10). Basically, the terminal must be at least 2.5M from the boundary of the premises, must not be under a carport, must not be lower than 2.1 Metres where there is a walkway, and must not be closer than 2.5M from a car parking space. It’s quite a helpful guide and cover mandatory and not mandatory aspects. Well worth a browse. It gives a couple of examples of typical dwellings - a Victorian house, and a modern detatched house.

David