Apologies Nest 2nd Gen install on Y plan system

Discussion in 'Electricians' Talk' started by Zedtechs1, Dec 6, 2018.

  1. Zedtechs1

    Zedtechs1 New Member

    Hi All,

    My first post on this forum (although viewed for a few years) so please go easy on me.

    My mate today gave me his Nest Gen2 thermostat and Heat link as he has upgraded to Gen3.

    Initially I thought this would be a simple swap for the existing thermostat until I realised the heat link needs wiring into the system. After reading all day I am viewing so many mixed ways to install that I feel I may be over complicating/ thinking this. And after speaking to a local plumber 'apparently' this cant be installed on my system (although think he couldn't be bothered.

    I have an Alpha boiler that is sealed for central heating and hot water is provided by a cylinder. The system communicates via the 'Drayton' programmer and the 'Honeywell' thermostat (wired). All the wires lead to and from the junction box that is in the airing cupboard.

    Now I Believe the Heatlink has to sit next/ near to the junction box and requires wiring for Live & Neutral, 'Call for heat' (terminal 3 in 3rd photo) and the common wired to live (terminal 2 in photo).

    Now upon opening the junction box I am met with the below (quite tidy) and wondered if the above is correct and which cables I should use to connect to the heat link.

    If you believe I may be out of my depth than please say so, but it cant be that hard?

    Attached Files:

  2. peter palmer

    peter palmer Well-Known Member

    Its more complicated than you think I reckon, you will probably have to shuffle a few red links about inside. if it was me I'd disconnect everything from the wiring centre and start again. There seems a few nondescript cables in there with all black cores, no easy task for a DIYer.

    I would follow a 3 port wiring diagram like this


    and match it up with the Nest diagram


    Noting you need to remove the original programmer and the original room stat but leave the cylinder stat in circuit.

    Note as well, the numbers on the top diagram programmer don't correspond with the nest diagram numbers. On the programmer 1 is HW off/satisfied (nest 4), 3 is call for hot water (nest 6), 4 is call for heating (nest 3).
  3. Zedtechs1

    Zedtechs1 New Member

    Thank you for this, and yes seems a bit more complicated than first anticipated!!

    Does it make any difference that I have a Gen 2 Nest which doesn't have the hot water terminals in the heat link? and therefore the programmer would have to stay.

  4. Mike83

    Mike83 Well-Known Member

    If the current wiring centre is correct and nest is doing heating only then,
    Fit a live and neutral to the nest then disconnect 2 and 3 in the wiring centre.
    Then common from the nest to 3 in the wiring centre. Then heating on from nest to 2 in wiring centre.

    You will also need to leave the heating turned on at the current programmer or link it out.

    How do you plan on providing power to the nest stat?
    Last edited: Dec 6, 2018
  5. Zedtechs1

    Zedtechs1 New Member

    Thank you Mike83.

    I suppose there is two answers to this;
    1) use the USB power supply cable or
    2) can the current cables that run to the room stat (2 and 3 in wiring centre if correct) be placed into the T1 and T2 on the nest heatlink

  6. Mike83

    Mike83 Well-Known Member

    Correct. If going for option 2 though make sure the neutral is made safe in the current wiring centre.
  7. Zedtechs1

    Zedtechs1 New Member

    Sorry Mike83, please don't shoot me down but which neutral cable are you referring to (1 in wiring centre)?
  8. Mike83

    Mike83 Well-Known Member

    The neutral that would go from the room stat to the wiring centre. It may not have one though.
  9. peter palmer

    peter palmer Well-Known Member

    Thought it was just gen 1 that didn't do hot water, obviously not.
  10. MGW

    MGW Well-Known Member

    Heat-link gen2.jpg I think version 2 is just a thermostat, so looking at flameports diagram L goes to L and 2, N goes to N, and SL goes to 3.

    As to if it replaces thermostat or is connected to wiring centre depends on you as the installer.

    The main problem is identifying wires in wiring centre, if they were as flameport shows 1 to 8 it would be easy, however often they are not. So normally you need to use the wiring colours on the motorised valve to identify which wire is which.

    So step one is to find out which system, not sure if diagram shown is Y or W, but there is also S and C plans, so to identify wires in wiring centre you need to work out which.

    It seems likely the system is Y plan and likely the white wire N/O call for heat so number 3 on the Nest, however I can't work out your wiring from picture, if me I would look at wire going into terminal 2 on wiring centre, it seems likely that is one wire going to thermostat? That should help identify the cable so you can use old cable to get 12 volt to new thermostat.

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