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Another Nest 3rd Generation Thermostat wiring Help needed!

Discussion in 'Plumbing and Central Heating' started by Kamen, 12 Sep 2019.

  1. Kamen

    Kamen

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    Hi Guys, I need help installing Nest 3rd Gen Thermostat wiring using existing wiring.

    Currently on Danfoss thermostat and nest installation guide is confusing. I believe our boiler system is in S plan.

    Our Boiler is Worcester 28CDi RSF COMBI.

    Our current Drayton thermostat switches on water heating automatically when hot woter required. And central heating works same way; if we require heating we switch on central heating.

    So need help in wiring Nest 3rd Gen Heat link first & then thermostat ring on existing wired thermostat.

    I thing to do this:
    1. Ls is as you suspect a permanent live (Ls = Live Supply) This would go to the Heatlink L,
    and also be linked to the 'Heating Common' 2
    2. Ns is 'Neutral Supply' This would go to the Heatlink N
    3. Lr is 'Live Return' this goes to Heatlink 3, "Heating Call for Heat"
    4. Earth to earth as applicable
    Dont know what to do with wire from Timer and Thermostat
     

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  2. muggles

    muggles

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    You don't have an S-plan, they're on systems worth hot water cylinders. Your existing thermostat doesn't switch your hot water, the boiler does that automatically when you turn a tap on.

    Your pictures are taken a little too close in so it's difficult to see where your existing wiring goes, but you need to trace the wires which go to your existing thermostat, as these will go to T1 & T2 on the Heat Link.

    Once your thermostat wires have been identified and connected to T1 & T2, the remaining wires from your timer to the heat link are

    L=>L
    N=>N
    1=>3
    4=>2
     
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  3. Kamen

    Kamen

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    Yes you are right about hot water ,I get the full wiring diagram now
    This stay as you say?
    and T1 & T2 ?
    I stop to here "My NEST" pic
     

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    Last edited: 14 Sep 2019
  4. flameport

    flameport

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    No idea where you got those from, but it's totally wrong.

    The correct wiring:

    worcester_combi_boiler_nest.png
     
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  5. Me neither, but must be Irish coz it’s a termostat, not thermostat :LOL::LOL:
     
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  6. Kamen

    Kamen

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    Which one is wrong , DIAGRAM.jpg is my current wiring i just identified all connections , a pic My NEST.jpg is my

    And to Nest Thermostat is going only 24 V power ? No other wiring to control ?
    And last not Irish I am Bg :D
     
  7. ericmark

    ericmark

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    When I came to wire Nest the first thing I found was the terminals are too small to take two wires in them, so I put a wiring centre below the Nest heat link so only one wire in each terminal. Well I fitted the Nest heat link next to existing wiring centre.

    Nest-thermostat-backplate.jpg The British nest thermostat back plate has just two connections, not the 10 you show, that is the USA version and I don't think it uses a heat link?

    Those two wires from T1 and T2 go to T1 and T2 on the heat link and it does not matter which way around. The most important thing is those two wires don't go to anything else. The earth on the Nest heat link is next to the T1 and T2 terminals and it ensures the wires between the thermostat and heat link can't pick up induced voltage and is only required if the thermostat is hard wired. However it does not connect to the thermostat.

    So you have 13 terminals, 1, 4, 5, 6, OT1, OT2, are not used with your combi boiler, you have just N, L, 2, 3, E, T1, T2 used likely you need to link L and 2. So 3 to Lr and L + 2 to Ls and N to Ns E to earth and T1 and T2 to thermostat.

    When I came to fit mine I started by identifying cables, so I knew which cable went from wiring centre to thermostat for example, then I wired cables from scratch. I found originally wiring was all up the creak, so it was not safe to assume wire A was from thermostat to wiring centre, so I tested very carefully the pair of wires before connecting to T1 and T2 at heat link to ensure open circuit and not connected to 230 volt, then also before connecting to thermostat tested to ensure only 24 volt on cables before connecting.
     
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  8. Kamen

    Kamen

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    This explain mine confuse
    That will do the work , and I thing to use new wiring and old one to leave one side
    Thanks to every one ;)
     
    Last edited: 16 Sep 2019
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