1. Visiting from the US? Why not try DIYnot.US instead? Click here to continue to DIYnot.US.
    Dismiss Notice

Oil combi with electric unvented

Discussion in 'Plumbing and Central Heating' started by Jakeh83, 23 Jan 2021.

  1. Jakeh83

    Jakeh83

    Joined:
    14 Jan 2016
    Messages:
    23
    Thanks Received:
    0
    Country:
    United Kingdom
    I have an oil combi 12/18 which doesn't really cut it for hot water having 2 bathrooms. Can i tee in an electric element only unvented to the hot supply? Or do i have to disconnect hot supply and leave one tap on boiler then pipe in unvented separately. Thanks
     
  2. oldbuffer

    oldbuffer

    Joined:
    6 May 2010
    Messages:
    1,273
    Thanks Received:
    463
    Location:
    London
    Country:
    United Kingdom
    1. If you add the output from an unvented cylinder to (effectively) the hot water output of a combi you would run the risk of pushing water backwards through either the combi or the unvented cylinder. So you can't do that. I don't believe non-return valves would help and could well be dangerous.
    2. You would have to separate the two hot supplies.
    3. Why not use the combi to heat an unvented cylinder? Say run kitchen taps directly off the combi, install zone valve(s) on the heating side, and run an unvented cylinder off that.
    4. Be aware of the pressure / flow requirements to run an unvented cylinder (2 bar, 20 lpm minima, properly measured) and the probable need to have a 22 mm cold feed to the cylinder.
     
  3. Sponsored Links
  4. oilhead

    oilhead

    Joined:
    29 Nov 2009
    Messages:
    2,052
    Thanks Received:
    489
    Location:
    Shropshire
    Country:
    United Kingdom
    Convert the heating circuit into a Y or S plan and install a cylinder to feed your bathrooms, keeping kitchen etc on the combi hot water. Whether you go unvented or conventional depends on cold supply factors but an experienced G3 registered plumber can advise.
     
  5. Jakeh83

    Jakeh83

    Joined:
    14 Jan 2016
    Messages:
    23
    Thanks Received:
    0
    Country:
    United Kingdom
    I have an unvented cylinder already from a job, it only has 2 elements and no coil. I was thinking of leaving the kitchen on the combi and putting the unvented on the bathrooms?
     
  6. Sponsored Links
  7. flameport

    flameport

    Joined:
    10 Mar 2007
    Messages:
    9,380
    Thanks Received:
    1,833
    Location:
    Poole, Dorset
    Country:
    United Kingdom
    Possible, but heating with electricity will be far more expensive than using the oil boiler.
     
Loading...

Share This Page