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Big Combi or System Boiler & Unvented Cylinder

Discussion in 'Plumbing and Central Heating' started by Lexonic, 31 May 2019.

  1. Lexonic

    Lexonic

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    Hello People

    First time posting on here but reckon you have the expert knowledge I need :)

    We've just moved into a new house, 30s semi. It currently has a standard C/H and H/W system: a working, but ancient Potterton Suprima boiler, hot water cylinder and cold water feed in the loft.

    We're planning a loft conversion and looking at replacement options. When complete we'll have:

    10 x rads
    1 family bathroom (1st floor)
    1 ensuite shower room (loft)

    We were planning on a decent replacement system boiler & and unvented cylinder (which we'd stick in where we currently have the hot-water cylinder - as this seemed to be the best way to guarantee good pressure to the loft shower (we had a similar set up in our last house).

    Howeve, a gas installer today was quoting on this work and recommended we consider a big Combi (Worcester Bosch 550cdi High Flow) as an alternative - as it would save us the space taken by the cylinder.

    We have excellent water pressure, so this doesn't sound crazy - but my wife and I are concerned that it's not going to give us sufficient flow to serve 2 x showers at once.... and that we'll end up with disappointing pressure in the loft shower.

    We're very much hoping to future proof as our kids have their teenage years ahead and we can only expect the hot water demand to grow!

    So what do you reckon?

    * Stick with the System Boiler/Sealed Cylinder (currently looking at ATAG 32i and 210 litre OSO Cylinder) OR
    * Go with the washing-machine sized 550cdi combi (and make some space stripping out the cylinder).

    Any and all advice would be hugely appreciated!

    Cheers,

    Lex
     
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  3. bernardgreen

    bernardgreen

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    Keep the cylinder. If it also has an electric immersion heater then you still have hot water when the boiler packs up.

    If considering a combi boiler then before you finally decide make sure you and the installer know exactly what will be needed to ensure enough gas can get to the boiler. A larger gas pipe may be necessary and it might be that this has to be installed externally along the walls of the house from meter to boiler.
     
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  4. durhamplumber

    durhamplumber

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    Seems to be a growing obsession and must have feature..BIZARRE
     
  5. fixitflav

    fixitflav

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    I'd go with the unvented cylinder, but not necessarily a system boiler. A set-up with heat-only boiler has the advantage of having the pump and expansion vessel separate, easier to diagnose and fix if something goes wrong. And probably fewer mods to the pipework.
    Why replace the boiler, if it's working OK? If you want to get rid of the F/E tank to free up loft space you can add an expansion vessel. If there's any concern about increased pressure with an expansion vessel on existing pipework and rads, it's the same with a system boiler (inbuilt expansion vessel).
     
  6. durhamplumber

    durhamplumber

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    Or go with a combi and wait 5 minutes.
     
  7. Lexonic

    Lexonic

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    @durhamplumber
    Not sure running 2 showers at once is that bizarre? I don't know about your house, but the morning routine requires military planning at ours!

    @fixitflav
    Fair point re keeping the old one. I'm no new-boiler obsessive. I nursed a 25 yr old Worcester Bosch for a good few years before :) But we have to move the boiler when we do the kitchen, and it doesn't seem to kick out enough hot water at the moment. Noted that heat only might be a better option. That was what we had before and it worked well. Cheers!
     
  8. ianmcd

    ianmcd

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    There are some great combis on the market at the moment, you would be better getting a professional in and asking for quotes for different systems, not pretend googlers on here
     
  9. StephenStephen

    StephenStephen

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    In terms of future proofing - aren't gas boilers eventually going to be phased out, and get replaced with renewable electricity supply, air source heat pumps, solar pv powered immersion heaters and the like? I think I'd be wanting a system with a tank so that those kind of technologies can be added in when the time comes...
     
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  11. flameport

    flameport

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    Perhaps, but it will be somewhere between decades and never before that applies to existing properties.
     
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  12. Lexonic

    Lexonic

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    Thanks all for the advice.

    I’ve had another local plumber in today and he’s confirmed my suspicions - he doesn’t think the Combi is going to provide the equal service to multiple outlets at once that I’m looking for.

    I think I’m going to pass on the system boiler too and go with a standard heat only boiler and an unvented cylinder with separate expansion vessel.

    Might well go far dual coil too so I can add solar down the line...

    Cheers!
     
  13. fixitflav

    fixitflav

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    Good call. Heating is too important to be left to heating engineers, googlers or otherwise!
     
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  14. ianmcd

    ianmcd

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    I want a new car which one would you recommend ?
     
  15. JohnD

    JohnD

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    A blue one. I find them the best.
     
  16. bernardgreen

    bernardgreen

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    That is a rather conservative opinion
     
  17. muggles

    muggles

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    No point having two showers in the house and only being able to use one at once
     
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