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Boilers: are heat exchanges only on central heating side?

Discussion in 'Plumbing and Central Heating' started by nickpowell77, 5 Feb 2013.

  1. nickpowell77

    nickpowell77

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    Hi - this may be a stupid question but are heat exchangers within boilers only used on the central heating side or also hot water?

    I have a Worcester Bosch boiler and has a water softner fitted 3 months ago. At my service I was advised that using water softners isn't allowed by Worcester Bosch because the aluminium will rot the heat exchangers - whether it does or not it invalidates the warranty!

    If the heat exchangers are only used on the central heating side then I will put in a t-junction to get hard water to top us the system.

    If they are used on both, I will rip it out and hit the installer over the head with it ! :evil:

    Thanks, Nick
     
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  3. mrgas

    mrgas

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    Your alright Nick. Run a hard water supply for topping up the heating system and use the softened water for your domestic (taps) use and all will be fine.
     
  4. D_Hailsham

    D_Hailsham

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    Is the water softener on the incoming cold mains?

    If so, and you have a combi (instant hot water) boiler you should not have a water softener as the softened cold water passes through the heat exchanger (that's how it get heated ;) ), which can get damaged.

    If you have a hot water cylinder, the cylinder itself is the heat exchanger as far as domestic hot water is concerned. The manufacturer of the cylinder should be contacted about whether a water softener is allowed.

    In either case the water permanently circulating through the boiler, radiators and the heating coil of a HW cylinder should not be softened.

    Do you also have a source of un-softened water?
     
  5. JohnD

    JohnD

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    you mean you were told the aluminium heat exchanger will rot due to the softened water?

    I remember seeing a link on here a while ago where scientific tests with softened water had actually been carried out (instead of relying on hearsay) and showed that corrosion inhibitors were effective with softened water.

    however I personally don't like aluminium in a boiler.

    An interesting article here http://www.sentinel-solutions.net/landingPage.aspx?id=13029&terms=softened
    about a quarter down the page.

    They also show (further down) that X100 protects against corrosion in softened water.

    see the summary at the bottom.

    This would not help, though, if you had a combi with an aluminium heat exchanger for the DHW. It would be interesting to know how many years it would take such an exchanger to block or perforate, and how that compares with the time taken to clog with limescale.

    Stainless steel is a far superior material.
     
  6. nickpowell77

    nickpowell77

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    Thanks for the response all

    I have a megaflow so I guess this is the heat exchange.

    I have a source of unsoftened water, so I will use this for the central heating system and use the softened water for my domestic hot and cold but I will check the megaflow first
     
  7. simond

    simond

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    Interestingly, a major UK water softener manufacturer told me that Worcester Bosch no longer had concerns about ion exchange softeners being used to fill up CH systems.

    Feeling they had a vested interest in that story, I rang WB up to check, and they reiterated their instructions not to expose the primary HE to artificially softened water.

    It'll be fine in the Megaflo. Won't stop it leaking though!
     
  8. nickpowell77

    nickpowell77

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    Do they leak ?
     
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  10. JohnD

    JohnD

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    the Megaflo is stainless steel, not Aluminium. Stainless is very resistant to corrosion, and softened water won't harm it. If you have a Megaflo I deduce you do not have a combi boiler.

    So I think the person who was trying to frighten you can only have meant the primary heat exchanger in your boiler (assuming it is aluminium). Sentinel say the their corrosion inhibitor X100 will protect it, even if it is made of Aluminium (my boiler has a stainless steel heat exchanger, which is why I bought it). I suppose you could also add X200 which will control the hard water limescale.

    The water in the boiler and radiators do not mix with the domestic hot water, so no worries there. If you want to connect the filling loop of your boiler to the hard water supply you can.

    mrgas got it first!


    I wish i knew if this was based on scientific evidence, or just a CYA. Do WB still use Aluminium?

    Edit:
    I suppose, even if they accept that the corrosion inhibitors work, they can't trust installers and householders to use them.
     
  11. simond

    simond

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    What is CYA? Do you have it?

    The excess salt dissolves the silicon/aluminium. Most WB boilers together with Buderus, some Vaillant, some Vokera, some Mains etcs have aluminium primary heat exchangers. The list is not exhaustive.

    Nearly every condensing boiler either has Stainless Steel or Aluminium guts to resist the ravages of condensate.
     
  12. JohnD

    JohnD

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    What excess salt?

    do you mean "dissolves" or do you mean "corrodes?"
     
  13. mehran

    mehran

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    Worcester Bosch heat exchangers pin hole all the time. the whole soften water/dirt/what ever excuse is just to try and get some cover for poor design.

    its a simply a weak heat exchanger design

    anyway it was put to the test:
    http://www.youtube.com/watch?v=5sDaExbPCWg

    guess what? no evidence of soft water corroding aluminium hx...
     
  14. JohnD

    JohnD

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  15. Agile

    Agile

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