Combi Boilers

Don't know about boilers for a house but I've got rented flats with combis and as is usual you get what you pay for. Have gone through Ariston, Saunier Duval, Ravenheat and some Italian one's I can't recall. None of them lasted more than 3 years and were a pain upto that point. Worcester Bosch or Vaillant appear to be the Naims of the central heating boiler world. Bloody expensive but very durable, generally no problems but great customer service when you need it. I think condensing boilers are the new thing and I vaguely recall the bloke trying to sell me on a combi for my house, whereby it keeps a small remote cistern always topped up and hot so that there's none of that combi time lag and 2 or 3 outlets can easily draw hot water simultaenously. Could be talking out of my bottom, but I think that the figures he was talking for the boiler and install for a house were in the region of £2k-£3k.

I got good advice here when I wrongly thought that I was getting hosed by my bloke.

http://www.plumbingpages.com/forums/ViewTopics.cfm?Forum=13

Hi John,
when our boiler went to it's maker a couple of years ago I also was impressed by the efficiency of the Combi Boilers and suggested to our Plummer/heating engineer that I would prefer that type fitted, but at the time his advice was to stick with the non pressurised system as due to the age of the house[ not as old as yours] he couldn't guarantee that the pipe work would stand mains pressure, and sure enough whilst fitting the new boiler he found one joint that had never been soldered and it was only the flux that had been holding it together for the past 30/40 years. So unless you can get your pipe work pressure tested first!! you can get a awful amount of water out of a 12mm pipe at mains pressure and Sod's law decrees "that it will only leak whilst your away from the house".
oldie.

We have a Vokera combi boiler, but our choice was limited if I recall correctly as we have to use LPG and this is not possible with all makes and models.

The advice we got from our plumber was that regular servicing by a reputable company (and a decent service contract for faults etc) was as important as any particular make. It did get a fault after 6 yrs use and was fixed smartly and cheaply by British Gas with minimum hassle so fair play to them.

Bruce

Call me mad, but despite dire warnings of excessive charging I was impressed by the surveyor from British Gas and had them install our condenser.
They were brilliant; a team of apparent experts in their own field turned up e.g. plumbers, electrician, roofer,etc. and did a fast clean efficient job. It was complex because we moved the boiler from the downstairs kitchen to an upstairs cupboard venting through the roof.
Don't forget you can't just poke a pipe through the wall and point steam at your neighbours if you want to stay on friendly terms.

Hi,
We pay out the £15 per month to british gas for their homecare thingy which protects the heating and boiler. No more than 3 months later sometning went wrong - they repaired it and the engineer showed me their cost proce for the item = £200!

This is one of those thing where we did as my mum told me LOL!

Also BG told us the thing had been installed incorrectly so the sub-contractors are back next week to rip it out and put it back again properly.

I don't think £15 PCM is alot to pay for covering something that I have no knowledge about.

andy c!

My experience is not bang up to date, but I see the issues as follows

Combi Boiler systems:

(1) Occupy less space
(2) Theoretically are more efficient as ONLY the water needed is heated

There are some potential drawbacks:

Since the water is being heated on demand (ie not stored)then

(1) Demand for a lot of hot water in quite a short time can be problematic

(2) As the system ages, and heat transfer rates may fall off due to , say , scaling, the impact on a combi system is dramatic....water flows more slowly, or outlet temperature is reduced


A "normal" gravity system uses a hot water cylinder as a capacitance to "iron out" sporadic mismatches between supply (ie boiler output) and demand. A falloff in efficiency is far less noticeable, since the only likely effect is that the tank takes slightly longer to heat up....you end up with the same volume of hot water


My own choice (given my natural conservatism (small "c")-) would be a gravity system...it is inherently more rugged and less "highly tuned" and in my experience, more reliable and easier to maintain. The "wasted" hot water is rarely wasted completely, and my viewpoint is that a little efficiency is worth scarificing for (in my experience) cheaper maintenance costs and better reliability

Amongst folk I`ve known who installed combis, all was fine for a few years...then....catastrophic breakdown requiring complete boiler replacement was not uncommon.

In my house, I inherited a system dating from the late 70`s....(a Baxi back boiler) I have the boiler serviced every 2 years...a few years ago I replaced a pump that was getting noisy ..cost..c £50...work done in 10 minutes.

The guy who services it thinks the system could carry on for very many more years

As for condensing boilers..I know little about them except the operating principle, and that in theory they should be cheaper to run. Do check the performance curves...some have an effeciency that deteriorates badly when operating outside a closely defined throughput.

Also compare the additional purchase price, likely repair bills over money saved in fuel.

It is often better to spend money on better house insulation and opt for a cheaper "less efficient" system....this could be the best solution overall in the long run

(I worked for a number of years on industrial hot water/boiler feed systems in power stations, so much of what I say above originates from my experience in this area)

laurie S

Hmmmm... some good advice.

One solution that was put to us by my father-in-law was a dual boiler system - a Combi for the 'open' system (i.e. taps, shower, etc.) and a regular boiler for the 'closed' system (i.e. radiators).

We're fortunate in that the current boiler is less than eight feet from all the taps, etc., in the 'open' system - so the runs are short. So a small Combi might work well there. Especially as it means that the disruption to update any pipework would be minimal.

However, looking at the link above (cheers for that, by the way) it looks like most plumbers don't rate combis, and as we don't really know how good our pipework is, perhaps a conventional boiler/tank for the central heating makes sense.

We've been having some work done installing a period conservatory/extension to the house, and in doing so discovered some crazy Victorian plumping madness. And somr more recent lunacy - such as the fact that to supply hot water to the kitchen, the pipes run outside of the house, under the ground, to come back in again. Basically 50 foot of pipe where 8 foot would have done. Madness. A real cowboy job!

John

We just had a Vaillant gravity boiler installed to replace our previous 25 year old boiler which finally packed in after requiring only the odd service and occasional replacement part. We initially considered a combi but all things considered didn't really fancy it. We're a family of 4 with a requirement for lots of hot water for bath, shower, lots of washing etc and the combi didn't really seem to handle that very well. Also the condenser system initially looked good although much more expensive but when I checked it out it seemed to me as though peak efficiency was only hit if the system's regularly running for long periods at a time and ours isn't.

In our case the best option was also the cheapest (if you can call £1900 cheap).

A point re: condensing vs. non-condensing: condednsing types are worth considering for total new installs, but I'd probaby not use one for a boiler replacement. The reason is radiator sizing, and pipework scale.

Condednsing boilers deliver more of the energy from the fuel burnt by getting the water vapour in the flue gases to condense. This requires quite cold return feed - which is best guaranteed by using oversize radiators and running the boiler near its design limit in terms of heating capacity. Otherwise you won't see a saving.

In my previous experience, combi boilers leave you washing your hands in cold water and just get warmish when you've finished.
I have just finished a new office building for my business with 2 storeys and underfloor heating. The plumbing contractor just went ahead and fitted a combi boiler, and to be honest, I haven't taken any interest in it at all, but it would seem that I do get instant hot water. I did wonder about this, so have just been downstairs to see about it. It is an Ariston Microgenius 47-116-14, whatever that is, but the notes tell me that there is a "comfort" setting that pre-heats water to get rid of the delay in getting hot water immediately. It works really well.
So now I know.
Seems OK to me. Beyond that I can't get excited about it.

I think you have most of the relevant info above. Take note of Martin's point - condensing boilers require a system specifically designed for them in order to get the benefits.

A couple of other point to note:

If your family have lots of baths, the heating is going to be off for 20-30 minutes as they run. This is noticable in older houses on cold evenings.

You can get showers that run directly from the boiler supply at mains pressure. Which is nice.

Regards
Steve

I have a Keston boiler with a presurised system, It is not gravity, and I dont think it is a normal combi as I have a tank.

What it does (i think) is heat a small amount of water to a very high temp, ie 75C, it then runs mains waqter through a heat exchanger in the hot water resovoir, this means that you get hot water straight away, without massive tanks.

They now do a system that integrates the boiler with this heat cylinder thingy, it looks like it would be simple to instal as it is an all in one unit.

So far my 4 year old kestom system in my new flat has worked without fault.

Hope this helps

http://www.keston.co.uk/products/duet.htm

Simon

http://www.keston.co.uk/products/duet.htm

Top Cat,

Choose a combi boiler.
Choose Vaillant.

I've no idea why some people have suggested the old fashion gravity fed method. If your radiators are that bad as to worry about 1 bar of pressure, you have problems waiting to happen and I would suggest you sort that out before you have a lake inside your house welcoming you.

A decent combi like Vaillant has no problem keeping up with my requirements. It has the option of keeping hot water stored, so you have it instant. If you think that's inefficient, think about the wasted energy of a storage heater.

Boilers are complex things and a decent one is worth buying in the long run. I've had mine for four years and no problems.

P.S. scale is non existent if you use X100 inhibitor.

Top Cat,
I'd suggest you get some proper professional advice as the appropriate solution depends so much on your own situation and requirements. From what you say (only two of you, not requiring constant hot water) it sounds like a combi is probably right for you where it certainly wasn't for my family. We would have had to pay much much more to get a combi sufficiently powerful to meet our requirements.

Frankly having seen a combi in operation I'm not impressed. One has just been installed in the toilets next to my office in work and it just doesn't do the job - if 2 or more people are trying to wash their hands at the same time (as is often the case) the pressure and temperature drop drastically. This would be totally unsuitable in my house.

We have a new house so the heating spec should be up to date.

A combi boiler in the garage feeds a large-ish storage cylinder in the house. As the hot water is drawn from the cylinder it is replaced by hotter water from the combi.

So far we have not run out at any time including having two kids and a dishwasher / washing machine on the go at the same time.

Just my 2p worth.

quote:

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I've no idea why some people have suggested the old fashion gravity fed method.

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Perhaps if you read my post you would

quote:

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... worth buying in the long run. I've had mine for four years and no problems.

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You think of four years as the long run?

Hmmmmm.......

Laurie S

Another point worth considering, you need to make sure that you have enough potential supply from your mains, if you have old pipe coming into your property they might be so furred up that as soon as you try and run a number of taps off the mains you are going to lose pressure, this could invlove getting a new mains supply fitted (your cost, most likely).

The mains pressure systems which invlove a hot water tank are the best of both worlds, mains pressure but lots of it. I've lived in two houses with Baxi boiler are they have been somewhat unreliable, suspect it was the installtion as much as anything else seeing the rest of the plumbing/building work that had been done by the same builders/plumbers. New lagging around your hot water tank and laggin around longer hot water run pipes (not central heating pipes) could reduce heat lose from the system (though this is simply heating your house so doesn't lead to much energy saving) but also mean less of the waiting for hot water.

Hope this is helpful.

Matthew

Couple of things:

We had a conventional CH/HW system installed in 1989 with a large, well-insulated storage tank, and one of the first condensing boilers on the market (Trisave Turbo 60). We went for a non-combi approach because we like powerfull showers, and as the water byelaws (ours -- Scotland may be different) prohibit "sucking" water out of the mains, a pumped shower has to be fed from a storage tank. Running costs have been extremely good, but (as mentioned above) the radiators were sized properly for a condenser -- they are most efficient when cycling on & off a lot around the t/stat set point.

Reliability of the Trisave has not been great, but the BG service plan has effectively given us about 1.5 new complete new boilers in parts alone since installation -- all at about 12 quid a month, so not bad overall.

If doing it again, I would do the same (ie; with a big storage tank with serious insulation, each shower pump fed with a separate outlet from the tank (Essex flange fitting -- sort of multiple spur equivalent), but I would definitely get a Vailant. Vailants are common enough to be non-intimidating to service personnel, yet overall quality and reliabity seems to be legend. I believe that they now produce a non-combi condenser to fit the bill.

If you like the shower experience you get in an American hotel, or (bizzare but true) on a French-run cross-channel ferry, you would be very lucky to get this from mains pressure alone.

Best;

Mark

come next april all boilers installed in england ( not sure about scotland ) will have to be condensing boilers with VERY few exceptions
the latest government drive !!!!!!!!!!!!!!!

neil

( someone who will have to fit the little bastards )