New boiler, condensing or combi?

Home Forum Chat Forum New boiler, condensing or combi?

Viewing 40 posts - 1 through 40 (of 40 total)
  • New boiler, condensing or combi?
  • Premier Icon 2unfit2ride
    Subscriber

    Morning all, I need to think about a new boiler as my existing one is probably 20 years old, my question is should I get a combi or a condensing boiler?
    The kids use a lot of water, shower everyday for about 15minutes each so I would also need to up the capacity of the tank if I go for a condensing one.

    Any Idea which would be cheaper to run, or install?

    Cheers.

    trail_rat
    Member

    better the devil you know if its not giving you gyp.

    Premier Icon nickjb
    Subscriber

    combis are condensing these days. I presume you mean combi or conventional. It’s more of a personal choice, I prefer combis. As above is the old one still working? Modern boiler are more efficient but you’ll struggle to pay back the savings and old boilers tend to go on and on

    allthepies
    Member

    What type do you currently have ?

    I looked into getting a combi but the amount of aggro it was going to involve converting everything to handle the higher pressures, change the gas piping (existing was too narrow diam) etc etc made it a non-starter.

    Premier Icon grizedaleforest
    Subscriber

    It’s an expensive decision to get wrong, so guess you should take professional advice. But I agree with above, unless your current boiler isn’t actually working properly, why change?

    Premier Icon 2unfit2ride
    Subscriber

    My current boiler is an Ideal W2000 RS40, I don’t know how old it is but it was here when we moved in 17 years ago. What has brought this on is a conversation I had with a mate at the weekend who changed his boiler & his bills have halved.
    I do have a combi boiler installed in the extension, & it is probably man enough to use as the main boiler for the house, but I don’t know if that is a good idea as the girls often shower at the same time albeit in different bathrooms.

    I will talk to a plumber & see what he recommends.
    Cheers.

    Premier Icon nickjb
    Subscriber

    I will talk to a plumber & see what he recommends

    I’ll bet you a pint he recommends selling you a new boiler πŸ™‚

    Premier Icon 2unfit2ride
    Subscriber

    That’s what I was worried about, hence the question above πŸ™‚

    crofts2007
    Member

    Had one at my old house, that was installed circa 1990.
    As long as the cast heat exchanger doesn’t die that boiler will last a bit (lot) more yet.
    Spares are still available.
    No complex control pcb, only a gas valve and pilot light system.
    Quite inefficient due to the pilot being on all the time, but as others have said it will be a long payback time to offset a new boiler.
    (Which probably will not last more than 10 years)
    I personally would have a conventional boiler instead of a combi, at least you have a fallback with a hot water tank that can be heated with an immersion if the boiler fails.

    tomlevell
    Member

    You could leave the combi to do what it’s doing then also use the heating side as a conventional boiler and pipe it to feed a cylinder (existing depending upon control or a new mains fed unit).

    Main problem with Combis is if they go down you lose all your hot water. Doesn’t sound like this would be helpful in your situation.

    Also have you tried heating the house less?
    Your control on the hot water is likely to be crude due to the age. A cylinder stat and timeclock would be a major help but may be difficult depending upon how it’s piped.

    globalti
    Member

    Boilers have become so efficient nowadays that I bet you wouldn’t see much difference between a combi and a condensor in terms of the cost for the thermal energy required to heat all that water.

    We upgraded from an old-fashioned iron core boiler to a modern condensor about 5 years ago and our gas bills dropped by about 30%. The boiler has been reliable and trouble-free, in contrast to the problems some people seem to suffer with combis if these and other fora are anything to go by.

    I definitely prefer having a cylinder full of hot water – it can be supplemented by the immersion heater and is fed water that has been pre-heated in a supplementary cylinder by my simple solar panel. The airing cupboard is a nice warm place to store towels and sheets and ensure kids’ clothes are nice and warm and dry. As somebody else wrote above, I wouldn’t want to run my heating system at more than normal gravitational pressure anyway because some of the original work was a bit dodgy.

    Premier Icon footflaps
    Subscriber

    I had with a mate at the weekend who changed his boiler & his bills have halved.

    You might get a 30% reduction from a more modern unit, but 50% sounds a bit enthusiastic. You could probably save 10% by just turning the thermostat down a degree or two.

    NB A new install will set you back Β£1000s, so it will take quite a few years to get your money back in lower gas bills (if at all as you’ll be lucky to get 5-10 years from a modern boiler before it dies).

    eskay
    Member

    In the same boat myself. The cast iron heat exchanger in my 30+ year old glowworm cracked on Friday.

    Thankfully there is an immersion heater in our tank so we still have got water.

    Premier Icon footflaps
    Subscriber

    The cast iron heat exchanger in my 30+ year old glowworm cracked on Friday.

    Mine starting weeping a couple of years ago from a crack, but has self-sealed with rust and seems fine.

    tron
    Member

    Second what the other guys have said. If you’ve got a working boiler, you will be waiting a very long time to get any payback from a new boiler install.

    eskay
    Member

    footflaps – Member
    Mine starting weeping a couple of years ago from a crack, but has self-sealed with rust and seems fine.

    Same! I first noticed a small drip a couple of years ago and it has held up since then.

    Friday morning it finally gave way (luckily I was still there as ten mins later I would have been cycling to work).

    The model I have was superseded in 1984!! I have had a good hunt around but cannot find a replacement heat exchanger unfortunately.

    northernmatt
    Member

    As said before all boilers now and condensing.

    You’ve got a heat only boiler so the easiest thing to replace it with is another one and keep all your current pipework. A Combi boiler to do the same job will probably, as others have said, require you to upgrade your gas run from the meter. The other option would be a system boiler and an unvented cylinder which is probably the best way to go but may end up costing more.

    If your current install is working then just keep it going but that appliance is getting to the stage where a lot of the parts will start becoming obsolete so start saving for a new one.

    Premier Icon grizedaleforest
    Subscriber

    Same! I first noticed a small drip a couple of years ago and it has held up since then.

    Friday morning it finally gave way (luckily I was still there as ten mins later I would have been cycling to work).

    The model I have was superseded in 1984!! I have had a good hunt around but cannot find a replacement heat exchanger unfortunately.

    Six months ago noticed water pooling by the 10 year old boiler. Heating engineer came, looked and said the heat exchanger was cracked and I need a new boiler. He quoted and I think I blacked out at that point. Happens that my builder was fettling in the house at the time and he said why not weld it up. He came along with his welding mate and sorted it out for a 100. Has worked a treat since πŸ™‚

    Premier Icon 2unfit2ride
    Subscriber

    Thanks for the advice everyone.

    Cheers.

    globalti
    Member

    My retired plumber neighbour tells me that in his day you could disassemble those cast-iron boilers and rebuild them with new gaskets. Not much different from an engine rebuild, then.

    Premier Icon footflaps
    Subscriber

    Gas regs require all boilers to have less than 1mb pressure drop to them, so it makes no difference whether to have a combi or not re-upgrading pipe work to 22mm.

    allthepies
    Member

    footflaps wrote:

    Gas regs require all boilers to have less than 1mb pressure drop to them, so it makes no difference whether to have a combi or not re-upgrading pipe work to 22mm.

    That may prove annoying when/if my 21 year old Potterton boiler packs up then πŸ™ The gas piping runs through a concrete floor I believe.

    wobbliscott
    Member

    If you’ve a family or live in a family sized house then go conventional. Combis are more efficient for small households in smaller houses where hot water demand is lower. They heat up the water at the rate that it’s consumed so take more energy to heat up a litre of water. If its a big house or a family home where hot water demands are higher it’s far more efficient to heat up a cylinder of hot water slowly, but only if you’re going to consume that amount of water each day.

    johndoh
    Member

    We just moved house and went from a combi to a conventional but we upgraded the tank to a pressurised cylinder – the difference is amazing – mains pressure hot water even when multiple taps are on. With the combi we could actually be in the situation where water wouldn’t even come out of the shower head occasionally.

    We decided to do it as the new place has two bathrooms and we have two kids so the new set-up seemed to suit our growing needs.

    I’d recommend it to anyone.

    alanl
    Member

    Wobbliscott, have a think about your Physics classes at school, and the amount of energy required to heat up a set volume of liquid.

    To heat up a bath full of water takes X amount of energy to heat it from 15 degrees to 55 degrees.
    That amount of energy is the same whether you heat it up slowly over 2 hours, or in 2 minutes.
    It can be argued that the combi boiler will be more efficient as it will have fewer heat losses while heating and (not) storing the hot water .

    Premier Icon footflaps
    Subscriber

    That may prove annoying when/if my 21 year old Potterton boiler packs up then The gas piping runs through a concrete floor I believe.

    You see quite a few houses now with the new 22mm pipe run around the side of the house and back in the kitchen. Saves a load of effort digging up floors / running it behind cupboards etc.

    johndoh
    Member

    To heat up a bath full of water takes X amount of energy to heat it from 15 degrees to 55 degrees.
    That amount of energy is the same whether you heat it up slowly over 2 hours, or in 2 minutes.
    It can be argued that the combi boiler will be more efficient as it will have fewer heat losses while heating and (not) storing the hot water .

    But surely there is a variable whereby the method of heating up said water is inefficient…

    trail_rat
    Member

    Johndoh – a shit combi is always a shit combi

    Had crap ones in rentals. Bought my own place and matched my combi to water use and throttled back the heating heating side ( its designed for that)

    Lovely hot water everywhere an nice low bills.

    johndoh
    Member

    Agreed, but a combi will always struggle when more than one person is using the water feed. That’s what we found – ours particularly suffered because we were on a shared feed with 5 other houses so on a morning when everyone was using water it was sometimes almost impossible to shower.

    Now I can just shower for as long as I want – the water heats up almost as fast as the tank drains πŸ™‚

    trail_rat
    Member

    Fair enough. I will admit i bought a stupid gert combi grant boiler for a 3 bed house….but its great !

    ali69er
    Member

    Combi, ours is awesome, mains pressure turned our shower into a power shower, whats not to like.

    divenwob
    Member

    Combi boilers have there benefits up to a certain point and then it megaflo time, surely the days of open storage tanks sitting above your head with the capability of bursting and flooding until turned off are numbered?
    Combis are perfect in the right situation and crap if you ask them to go past there designed usage, so what are your needs?

    trail_rat
    Member

    Just found it we got the grant vortex pro 26e

    All we really needed for the heating was an 18kw or possibly 21 iirc but the 26 gives us the water we wanted at the expense of a little effiency on the heating circuit- which tbh is raely ever on bar an hour in the morning πŸ™‚

    My previous one to quote my heating engineer “if this was a gas boiler id have to condemn it – do not ever work in this garage with the door closed “

    Although as you say mega flo are the nuts – tempted to put one ( or similar) in on a solar circuit and then use the combisol kit to blend the systems πŸ™‚ – boiler would possibly end up an expensive paper weight πŸ˜‰

    wobbliscott
    Member

    Alanl in theory yes , but in reality you need to put more in. does it take the same amount of energy to accelerate a car from 0 to 60 in 3 second as 6 seconds? The speed at which you heat something up affects the energy required. If you want to raise the temp by 1 degree in half a second you’re going to need more energy as things are not 100% efficient in the real world. Combi boilers tend to be rated at higher BTUs than conventional boilers for this reason.

    Premier Icon mikewsmith
    Subscriber

    wobbliscott – Member
    Alanl in theory yes , but in reality you need to put more in. does it take the same amount of energy to accelerate a car from 0 to 60 in 3 second as 6 seconds? The speed at which you heat something up affects the energy required. If you want to raise the temp by 1 degree in half a second you’re going to need more energy as things are not 100% efficient in the real world. Combi boilers tend to be rated at higher BTUs than conventional boilers for this reason.

    Physics would like a word…

    It takes the same amount of energy to change the temperature/move something.

    Assuming no heat escapes (which in the case of a kettle is obviously not the case), in general, it makes no difference whether you heat something slowly or quickly. All substances have a certain heat capacity, so it takes a certain amount of heat energy to raise their temperature by a certain amount, regardless of the time taken to raise the temperature.

    EDIT http://en.wikipedia.org/wiki/Heat_capacity
    /Edit
    Inefficiencies and losses will be harder to track, ie will you waste more over a longer period of heating. How much heat loss are you accounting for your tank of water etc.

    and to the OP couple it with a solar hot water system πŸ™‚

    toys19
    Member

    Combi boilers tend to be rated at higher BTUs than conventional boilers for this reason.

    Aside from the obvious physics mistakes detailed above, I wonder how you are able to make this statement confidently? Do you know any combi designers, and are familiar with their thought process?

    trail_rat
    Member

    He is kind of right – but for the wrong reason

    The combi has a higher btu rating in most cases if the plumbers worth his salt and has done hismath.

    On demand Dhw usually higher btu than the heat loss in the house.

    Means the heating side is usually over specced to supply dhw to two showers.

    With an indirect tank you can heat it slowly so the dhw btus required isnt that important.

    Horses for courses but i wanted my boiler out side and my kitchen cupboard back !

    Premier Icon DaveRambo
    Subscriber

    I had the exact same thought process about 2 years ago.

    One plumber told me the problem was the old boiler being inefficient which is complete rubbish. Another agreed with me that as long as it was safe it was fine.

    The payback time meant it would have been cheaper to pay higher bills.
    What made my decision to have it replaced was a lack of some spare parts.
    A plumber who spoke sense said it was worth thinking about changing in the next few years as a failure of some parts that he was seeing would mean a new boiler.

    When I swapped I also like the idea of a hot water tank etc but decided for a Vaillant Combi – It means we have endless hot water a much simpler heating / hw system and much better hw pressure.

    So far we had a pump replaced under warranty and last week the pcb changed as it was playing up. Slightly annoying given Vaillant are supposed to be v reliable but overall happy I changed from a standard system boiler/hot water tank to just a combi.

    Premier Icon footflaps
    Subscriber

    What made my decision to have it replaced was a lack of some spare parts.

    You can just use generic parts in most cases, eg the pressure switch went in my 25+ year old Potterton, so I just replaced it with a generic part and cable tied it in place.

    divenwob
    Member

    Combi’s need to be higher rated to be able to heat the DHW as required,they are pretty much a system boiler combined with an instantaneous water heater,hence the name.A 12kw combi would be a tad slow at heating a bathful of water.The key thing with a combi is domestic hot water flow rate,some are capable of delivering around the same amount of litres per min as a decent cylinder, a wier guage will tell you if you have enough flow to make it a good choice.

Viewing 40 posts - 1 through 40 (of 40 total)

The topic ‘New boiler, condensing or combi?’ is closed to new replies.