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Combi in series with unvented hot water cylinder

Discussion in 'Plumbing and Central Heating' started by Logidex, 20 Oct 2021.

  1. Logidex

    Logidex

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    Hi,
    I have a 2 bed flat which has an Ideal system boiler coupled with an unvented hot water cylinder. Due to it's location, the boiler has a twin flue setup. The boiler has packed up so I need to have it replaced with another twin-flue boiler. This limits the choice somewhat and I'm thinking of going for a Keston 30kW boiler.

    I noticed that the price difference between a system and combi versions is just £100. I'm happy to pay the extra if it can be of any advantage: I'm thinking I could in the future have the HW cylinder removed to free up storage space in the airing cupboard and simplify the plumbing. The Keston should be able to deliver a healthy flow rate for a flat.

    My question is: can the combi be installed without connecting the secondary HW pipes in the meantime?

    If the anwer is no, the secondary system has to be connected up, I have a secondary question:
    Can the output from the HW cylinder be fed into the boiler input so that the two circuits are connected in series?
     
  2. muggles

    muggles

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    Your first question should be "is the existing flue system compatible with, and approved for use with, the boiler I'm proposing to have installed?". Keston use a very different type of twin flue system to other manufacturers, and you're not allowed to mix and match. It's highly unlikely that the old Ideal system will be approved for use with a Keston.

    Having established that, and answer to your next question is that it depends on the boiler manufacturer. Whilst it will work, some will invalidate the warranty if it's not connected up.

    The answer to your second question is similar - it depends on the manufacturer and whether they have any limitations on inlet temperature. Either way you'd be better off having the cylinder removed as part of the boiler installation job if that's the way you want to go.
     
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  4. Logidex

    Logidex

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    Thanks Muggles. Already asked that first question and know that new flue system needs to be replaced even if new boiler is from Ideal.
    The property is a rented flat with tenants in situ. So wanted to keep work mess and duration to minimum.
     
  5. muggles

    muggles

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    If you're replacing the flue system anyway then there are much better options out there than the Keston. Have a look at the Intergas Xclusive, which has the advantages of being a combi which can be run as a system boiler with the hot water circuit empty whilst maintaining the 12 year warranty, a simpler overall design with only 4 moving parts, a more robust heat exchanger, has better modulation ratios which will make it cheaper & more reliable to run, has a twin flue option, and isn't a Keston.
     
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  7. ianmcd

    ianmcd

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    I wouldnt fit a Keston if I got it for free, and yes I know the new ones are ideal logics, a massive step forward :rolleyes:
     
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