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Big Refurb - Should I convert to sealed system

Discussion in 'Plumbing and Central Heating' started by letsddp, 15 Sep 2020.

  1. letsddp

    letsddp

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    Hi,

    About to embark on a refurb of the house including extension and wanted to get some views from you guys:-

    + Would you recommend moving to a sealed system (assuming budget is ok)?
    + If moving to a sealed system do i need to re-pipe the house? Is there a way to test the current pipes can handle the pressure? Does re-piping the house require all walls and floors to be teared down?
    + Is it true that i need an additional line in from the mains supply to the sealed system?

    Any help much appreciated, apologies in advance for the dumb questions (complete novice here)
     
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  3. sxturbo

    sxturbo

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    do you want to go combi boiler or stay with the hot water tank?
     
  4. letsddp

    letsddp

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    Hi, thanks for responding. Would be beneficial to remove the F & E + hot water tank so we can use the loft space and airing cupboard. Boiler we were going to change in any case so can go either way whatever works best.
     
  5. sxturbo

    sxturbo

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    if you go with combi your hands are tied and will have to swap over to a sealed system. When installing a combi you will have to run a new cold water feed to the boiler from the existing mains, but this isn't a massively expensive task, though is dependent on the location of the boiler, a lot of people like to relocate the boiler to the airing cupboard (its a lot smaller than the old hot water cylinder, and if its on an external wall its easier to run the gas pipe up on the outside, and the mains can be brought down off the old cold water tank feed.

    you wont need to replace all your pipework, although it is worth knowing that their may be a possibility that joints may leak, though this isnt that often, my house a friends and my parents house all swapped over to sealed systems and our houses were built in the early 70's and all were fine.
     
  6. sxturbo

    sxturbo

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    if keeping the hot water tank, you can still go for a sealed system boiler (this means the pump is built into the boiler) you will have to run a cold water feed into the central heating system, but this is easy and can be taken off the cold water tank feed and dropped down into the airing cupboard and connected via a filling loop into the central heating system.
     
  7. letsddp

    letsddp

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    Ah thats good to know, ours is late 70's build but the pipes (have looked inside) do see fairly loaded with junk. I guess worse case is to convert and then check for leaks and spot fix vs re-pipe the whole lot?

    Just wondering is it worth re-piping anyway but not sure what that involves and if the entire house need ripping down in order to do it
     
  8. sxturbo

    sxturbo

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    depends on where the pipes run,

    it will be a case of all the floors up, and usually at least 1 wall where the pipes run to the down stairs.

    you will require a power flush if the pipes are that blocked,

    i'm sure others with more knowledge than me will advise if the pipes can be pressure tested, i know of a way doing it, its just whether heating engineers do it
     
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  9. letsddp

    letsddp

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    Thanks sxturbo much appreciated.
     
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  11. oldbutnotdead

    oldbutnotdead

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    Few things to think about if you change your hot water system;
    Check your mains cold water dynamic pressure and delivery rate- if you go combi (no tanks, no cylinder) or unvented dhw (no tanks) you'll be relying on mains pressure to drive showers etc. If you're at or near minimum service obligation (10 litres/min at 1 bar) your shower experience will be disappointing compared with your current setup.
    If you have more than 1 shower room you'll need either a massive combi or a cylinder (vented or unvented).
     
  12. letsddp

    letsddp

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    Hi oldbutnotdead, thanks for responding. I was assuming we have to get an unvented tank (e.g. megaflow) and put that in garage. Would i still need min bar at the mains for that? Shower rooms would be three in the house.
     
  13. oldbutnotdead

    oldbutnotdead

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    Yes you do. At the moment (assuming you have thermostatic showers) hot and cold pressure are determined by how high the header tank is, flow rate is determined by pipe sizes & headloss in the pipes. If one or more showers were a bit weedy you could install shower pumps to your hearts content.
    Unvented cylinder- hot and cold water pressure and flow rate determined by mains water pressure and internal pipe headloss. Very limited pump options if shower(s) underperform.
    EDIT You can have whatever system you want as long as you have the space to house the bits. Combis and unvented cylinders are space savers designed to suit tiny houses and flats, the trad vented cylinder & header tank gives you more flexibility & makes you less dependent on the external water pressure
     
    Last edited: 17 Sep 2020
  14. letsddp

    letsddp

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    Thanks oldbutnotdead. My cold water tap closest to the mains seems to come out at some pace (appears high pressure) can i assume that showers would be similar or perhaps a little off that -10%. Also you may know this but is there a way to test if my existing pipes can even handle an unvented system?
     
  15. oldbutnotdead

    oldbutnotdead

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    The way to check pressure/flow needs a pressure gauge on the cold water supply & a large bucket. Run the tapfull bore for 30 seconds, see what pressure is reading & how many litres you get in the bucket. 2 bar and 15 litres will be OK, more or higher is better
     
  16. letsddp

    letsddp

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    Ok thanks, what about whether my pipes can handle a sealed system vs what it was installed to do which is vented?
     
  17. oldbutnotdead

    oldbutnotdead

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    99.99% of the time you'll be fine going to pressurised hot water. Might have to change any modern taps (lever types) that are more sensitive to high pressure. Any old school taps will work fine.
    You might get the odd compression fitting weeping a bit with the increased pressure but v unlikely to have anything go catastrophically wrong
     
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