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Better storage combi than vaillant ecotec plus 938?

Discussion in 'Plumbing and Central Heating' started by otherparty, 28 Mar 2017.

  1. otherparty

    otherparty

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    I have a two-bathroom four-bed house (with hydro UFH on GF and rads upstairs) and have decided to go for a storage combi. Realise many prefer an unvented cylinder system, but i'm sure a storage combi will be fine for my needs. The Vaillant 938 has been suggested to me, but i was wondering if there are any alternatives i should consider, e.g. Worcester or Viessmann etc.
     
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  3. Agile

    Agile

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    I would suggest the Viessann 222 but every installer has their favourite.

    But my recommendation would be an unvented cylinder. They have the advantage of an immersion heater in case the boiler is faulting. Could be a little cheaper too.

    But whatever you get the water supply has to be adequate. Normally a minimum dynamic flow rate of 22 litres per minute @ 1.0 bar.

    Tony
     
  4. Don't bother with a 222
    Better to fit a 100 or 200 4 pipe system boiler and 90ltr unvented underneath. Will take up the same space be cheaper and better.

    If you are looking for wall hung,
    Viessmann do a 111 seems a descent kit. The 938(I've not seem but assuming its replacement for 937) is like a washing machine on the wall.
    The V111 is same depth as standard but wider.
    Both will require some solid fixings to hold them to the wall.

    Not a fan of the Worcester storage combis (or anything) myself. And again floor standing.

    Before you commit, make sure you fully understand the limitations of a storage combi.
    The flow rates given are generally for a short period until the store is depleted at which point the 938 becomes a 838 and a 111 becomes a 100 combi.
    If you run 2 showers at once the store will deplete quickly and you'll have a fairly disappointing 2 showers after that.

    As Tony suggests have you had your water supply tested.
     
  5. otherparty

    otherparty

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    Thanks, guys. When builders tested the outside tap, i had 6 bars of pressure. Nowhere near that inside, but have had a 'blue' pipe put in from the external stop valve. My issues are mainly cost, but also floor space. Also, i don't have a family (yet!), so running two showers at the same time will not happen very often.
     
  6. otherparty

    otherparty

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    PS, new plumber is going to start work soon. Is it just the pressure and flow rate i should get him to test?
     
  7. otherparty

    otherparty

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    Duplicate post - sorry!
     
  8. Agile

    Agile

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    He should test BOTH at the same time.

    Some don't know how to.

    Tony
     
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  9. otherparty

    otherparty

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    I may be missing something, but, if just one bath takes 200+ litres, wouldn't a 90-litre unvented run out of hot water before the bath is full?
     
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  11. Geronimoe

    Geronimoe

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    Must be a big bath for 200 litres.
    Average bath is 80 litres and don,t forget your mixing cold in with the hot from cylinder.
     
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  12. otherparty

    otherparty

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    OK. Thanks. I was looking at the capacity figure for my 1700x700 bath which is 228l. But what you say makes sense:
    "According to BS6700 a standard 1700mm x 700mm bath uses approximately 100 litres of water at 40’C. This is split into 60% hot and 40% cold water when hot water is stored at 60’C."
     
  13. Geronimoe

    Geronimoe

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    Don,t forget to take in your displacement and overflow height into your calcs
     
  14. Also don't forget to take into account a viessmann 100/200 4 pipe with hw priority and the correct hot water cylinder has endless hot water;)
     
  15. otherparty

    otherparty

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    How does that work? And what cylinder would you recommend if i go that route instead?
     
  16. Viessmann or gledhill.
    But ultimately any high recovery cylinder with a suitable sized coil.

    I mostly Use 150ltr cylinders but will easily fit cylinder and boiler in airing cupboard.

    It will provide you with endless hot water.

    Google viessmann 4 pipe.
     
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  17. Agile

    Agile

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    That "endless hot water" is ultimately the hot water flow that the boiler power can heat.

    So with a 24 kW boiler that is about 7-8 litres per minute!
     
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