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Nest V3 and Vaillant EcoTec Pro24... a simple question.

Discussion in 'Plumbing and Central Heating' started by DIFM, 27 Jan 2019.

  1. DIFM

    DIFM

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    Hi all,

    Does the Nest V3's live and neutral HAVE to be connected to the bolier PCB's L/N as in this diagram...


    ...or can it be connected to an alternative L/N supply? (EG a 13 amp plug socket)

    Many thanks.
     
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  3. Crofton Gas

    Crofton Gas

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    Doesn't have to come from boiler supply, although it's easier to just run 4core from the boiler to stat.
     
  4. DIFM

    DIFM

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    Thanks for clearing that up.

    Out of interest, I can see why you would run 3-core (L, N & RT) but why 4-core... what would the other core be for?
     
  5. Crofton Gas

    Crofton Gas

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    Save trying to get a link wire across from live to 2 in nest,
    Live - L
    Neutral - N
    Live out - 2 (terminal on same plug a RT)
    RT- 3
     
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  7. DIFM

    DIFM

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    Gotcha, thanks for your help.
     
  8. DIFM

    DIFM

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    Nest installed and up and working.

    Although the thermostat is reading the current temp as 23 whilst the old Boss one says it is 19...very weird.
    It feels more like 19 than 23, that's for sure!
     
  9. stem

    stem

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    The Heat Link should really be connected to the same 3A fused supply as the boiler, but the wires don't physically have to come from the boiler PCB terminals, but can come from directly from the fused spur itself.

    From the ecoTECH Pro manual:

    instructions.JPG

    The Nest wiring diagrams also all show a common supply for the boiler and Heat Link

    Capture.JPG

    If there are two power sources connected to the Heat Link, someone may isolate the power to the Heat Link and open it up and receiver an electric shock because there are still wires from the boiler that are 'live' connected to it.

    In rare instances for certain items of equipment where it is unavoidable to have more than one supply, a label should be affixed to provide an alert to the danger.

    sign.JPG
     
  10. DIFM

    DIFM

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    Thanks for this point.

    When I actually came to install it I did indeed power it from the same fused spare as the boiler...I just replaced the Siemens heatlink with the nest, and ran a single wire from the nest to the boiler and removed the Siemens contro, wire from the boiler.
     
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