new boiler: open vent or system boiler

Appreciate some advice here.

Currently have a conventional gravity fed system with floor standing thorn emi conventional boiler (open vented). Looking to upgrade the system to a modern set up.

Its a large house and so a combi is out. Will be using a water cylinder (current one is big enough).

I don't really understand the system boiler vs open vented option.

As far as I can see the only advantage is the loss of an expansion tank in the loft. We have no intention of building in our loft.

Are there any other issues I should understand?

TIA
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Comments

  • Hi.

    On the plus side.

    Reduces the risk of freezing the f&e tank in the roof (but you still have the main tank).

    The system can be pumped harder as there will be no pumping over or air pulled into the system.Improved system circulation with higher pump speed.

    Less oxygen in the water so reduce corrosion risk.

    In the event of a leak on the system only the contents of the system will leak out, rather than the f&e tank constantly filling.

    Downside.

    Only one downside really. The system and it's pipework.
    The increase in pressure (the pressure relief valve will operate at 3 bar (42PSI ish) will find out any weakness that was quite happy to sit at gravity pressure.

    The system will run between 1 and 2 bar.

    GSR
    Ask to see CIPHE (Chartered Institute of Plumbing & Heating Engineering)
  • ormus
    ormus Posts: 42,714 Forumite
    with large houses (two bathrooms) it can make a lot of sense to split the house into two zones and install 2 x combi boilers.
    with the added benefit of one boiler always working in case of breakdown.
    Get some gorm.
  • ormus wrote: »
    with large houses (two bathrooms) it can make a lot of sense to split the house into two zones and install 2 x combi boilers.
    with the added benefit of one boiler always working in case of breakdown.

    Hmm
    I personally think that's just a tad overkill, as well as expensive.
  • ormus wrote: »
    with large houses (two bathrooms) it can make a lot of sense to split the house into two zones and install 2 x combi boilers.
    with the added benefit of one boiler always working in case of breakdown.

    This is the 2nd thread that I've seen where you have recommended someone fit two combi boilers, what is the matter with you, if a house has enough hot water demand to warrant two combis then a combi isn't the right option in the first place, I would never ever fit two boilers in a domestic property, I don't know what you do for a living but if you are in the plumbing & heating industry I bet your customers love you with all your incorrect advice.
    I'm only here while I wait for Corrie to start.

    You get no BS from me & if I think you are wrong I WILL tell you.
  • ormus
    ormus Posts: 42,714 Forumite
    compared to the total cost of a system,
    the added expense is fairly small, two small/er combis are not that much more than one large one.
    and the benefits are greater than the extra costs.
    Get some gorm.
  • The cost of getting 2 mains feeds in the house and siting 2 combi's seems like a lot of hastle to me.

    I can see your point of having a system if one fails but I am not at all convinced that combis are the right thing for large houses with multioccupancy.

    I will stick to 1 condensing boiler and am just trying to get a feel for the real world differences between a gravity fed open vented boiler or system boiler.

    My central heating system is low pressure radiator based and now 25y old. I would be a bit concerned about putting high pressure through that system.
  • ormus wrote: »
    compared to the total cost of a system,
    the added expense is fairly small, two small/er combis are not that much more than one large one.
    and the benefits are greater than the extra costs.

    NO, NO & NO what a b1oody stupid idea
    I'm only here while I wait for Corrie to start.

    You get no BS from me & if I think you are wrong I WILL tell you.
  • tired dad, some good advice & explaination from CH above, i'd just stick with open vented if you are at all worried about the rads or pipework, i've seen rads explode when coverted from open vented to sealed with the increased pressure.
    I'm only here while I wait for Corrie to start.

    You get no BS from me & if I think you are wrong I WILL tell you.
  • garethgas
    garethgas Posts: 2,477 Forumite
    ormus wrote: »
    with large houses (two bathrooms) it can make a lot of sense to split the house into two zones and install 2 x combi boilers.
    with the added benefit of one boiler always working in case of breakdown.

    I don't mean to join in any kind of ganging up, but in 35 yrs, I've only needed to do this twice.
    In one case, the meter needed to be replaced with a bigger one to cope with the gas demand.
    I think you should reconsider your view on this as its a very rare and unusual situation that would require 2 boilers in tandem.

    keithgillyon wrote:
    NO, NO & NO what a b1oody stupid idea

    Harsh but true I'm afraid.
    You have been reading.....another magnificent post by garethgas :beer:
  • cyclonebri1
    cyclonebri1 Posts: 12,827 Forumite
    Op, you say the house is too large for a combi boiler??. Just how big is it??

    Only last year we fitted a Glow worm combi to my daughters newly extended house. It has been massively extended having 5 double beds 20ft x15ft lounge, large kichen, large dining, 2 bathrooms, 2 kids playrooms, office and open reception.

    The combi, excuse the lack of detail as it escapes me at present, copes perfectly well, and would likely be much more efficient now condensing boilers have improved.;)
    I like the thanks button, but ,please, an I agree button.

    Will the grammar and spelling police respect I do make grammatical errors, and have carp spelling, no need to remind me.;)

    Always expect the unexpected:eek:and then you won't be dissapointed
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