Nest 3rd generation wiring up - help please

Discussion in 'Electricians' Talk' started by bmrpl, Nov 14, 2018.

  1. bmrpl

    bmrpl New Member

    Hello.

    Sorry if this is going to be yet another post about wiring up a nest thermostat. I got a 3rd generation the other day and started to change my existing honeywell unit next to the boiler for heat link and Drayton thermostat in hallway for the nest itself when I got confused with amount of wires. So there are 3 neutral wires and 2 live connected to the honeywell bracket - do I need to connect all of these to the heat link? If so there's not a lot of space in the connector... If that's the case, the ones in corridor are 230V live / neutral wires which I will isolate prior to nest connection and only use the other 2 for 12v.

    I have Potterton Promax CombiHE Plus Combi boiler.

    Thank you, any help will be much appreciated.
     

    Attached Files:

  2. bmrpl

    bmrpl New Member

    Afternoon,


    I've done some more homework and understand much more about the installation now.


    The combi boiler I have is Potterton

    Promax Combi HE plus


    I have programmer - Drayton LP711 with lots and lots of cables :

    3x neutral (2x blue and 1x grey)

    2x live (dark brown and light brown)

    1 - common (light grey)

    3 - call for heat (brown)

    There also 2 earth cables at the back of the box and 2 black cables connected together in a block


    Thermostat in the hallway Drayton RTS1 with the below:

    Neutral (grey) which is not needed and will be insulated in terminal block

    Live - black

    Brown in number 3 which is switched live (call for heat)

    Earth which I will put in terminal block


    So of course the programmer will be replaced with heat link and the thermostat will be swapped for the nest itself.


    From what I understand I need to connect both live cables from the programmer box in a connector block and then feed one cable to live in the heat link

    Similarly, neutral - all 3 in connector block and then with a single cable to my heat link.

    Common cable - light grey - from 1 on programmer goes to number 2 on heat link. I also need to use a jumper cable between live and 2 on heat link.

    Call for heat goes from number 3 on programmer to number 3 in heat link.


    I will be using existing cables from thermostat to connect to my nest controller. I am not too sure about this connection though as I will be using the black and brown only but at the moment these are 230V I guess and I only need 12V for the nest.


    Which cables are going to T1 and T2 in heat link please? Do I need to connect earth to the heat link at all? Everything is plastic and the nest won't even have earth connected...


    Thank you very much for any help in advance!
     
  3. Mike83

    Mike83 Screwfix Select

    Black and brown at the current rts1 need to be identified at the current programmer.
    These 2 wires will be t1 and t2.
    Everything else you say sounds fine but no jumper required as power to nest 2 is supplied from boiler via common
     
  4. bmrpl

    bmrpl New Member

    Thanks a lot Mike83,

    Where do I look for the cables to plug in to T1 and T2? Would the black one be one of these in connector block at the back? There's no other black ones by the programmer...
     
  5. Mike83

    Mike83 Screwfix Select

    Yeah it will be.
    A multimeter would test for continuity identifying the cable or just a process of elimination.
     
  6. Mike83

    Mike83 Screwfix Select

    This is just a 20 minute job for a spark/heating engineer so if your unsure maybe call in help.
    You need to ensure you identify each wire
     
  7. bmrpl

    bmrpl New Member

    Thanks Mike83,

    I'm capable of that, I just guess it'll take me twice as long plus was hoping that someone would know just by looking at it! Going to get a multimeter right now before screwfix closes at 4
     
  8. Mike83

    Mike83 Screwfix Select

    Your set up just looks a little different from usual.
    Usually when there’s a terminal strip behind the programmer this is because the room stat is wired in to the programmer.

    1 on the old programmer should come from the boiler.
    3 on the old programmer usually goes to live on the room stat (colours don’t marry though).
    3 on room stat then goes to terminal strip behind programmer.
    Other end of terminal strip then to boiler as switched live.

    But with 3 on prog and live on stat not matching it’s been done a bit different.
     
  9. bmrpl

    bmrpl New Member

    Everything is unusual in this bloody house lol. Earlier on had to replace bathroom fan, from a simple one to one with timer and humidistat. Couldn't get it working ok (the extra functions that is) as whoever was installing appliances swapped cables in junction box.

    I'll have another look at what you just said and go from there. I'm determined to get it sorted so bear with me ;)
     
  10. bmrpl

    bmrpl New Member

    So if I follow correctly, one of the neutral cables from the bunch of 3 from the programmer would end up as the neutral in my stat box, right?

    If that's the grey one - and color would match then I can theoretically use this cable to connect to either t1 or t2 and to my round nest in the hallway together with the brown one and not to worry about the black one which I could then terminate and leave isolated. I know that this is not ideal and hopefully none of electricians would do it like that but should do the job?

    I'm not going to connect it and just see what happens of course, l but will check the continuity first
     
  11. Mike83

    Mike83 Screwfix Select

    Correct. The grey more than likely goes from the programmer to the stat.
    But there’s no reason to use the grey.
    You’ll need to split the blacks in the terminal strip and reuse the one going to the boiler. You may as well use the other one also.
     
  12. Mike83

    Mike83 Screwfix Select

    What you should end up with is,
    A LNE into boiler.
    A LNE into heat link.
    2 wires from heat link t1 and t2 to new stat.
    A live out from boiler to heatlink 2.
    A live return to boiler from heatlink 3.
     
  13. bmrpl

    bmrpl New Member


    So if I split the blacks and one will go from heat link to the nest, what do I do with the other half of the black cable?
    Sorry for asking daft questions
     
  14. Mike83

    Mike83 Screwfix Select

    Other half should got to 3 on the heatlink as it goes to the boiler.
     
  15. peter palmer

    peter palmer Screwfix Select

    I'd be very careful, it looks a little odd to me too, the 3 core at the stat is solid cable but the grey at the programmer looks stranded, maybe flex. You might want to make doubly sure where each wire goes as the Nest will protesteth strongly if it gets 240 volts down its 12V rail.
     
    Mike83 likes this.
  16. bmrpl

    bmrpl New Member


    You are right Peter,

    All the stats cable are solid and in the programmer I have a mixture. As far as I remember the grey on the very left in programmer is solid as well. I will do the continuity test and go from there, not planning to blow anything up
     
  17. Mike83

    Mike83 Screwfix Select

    This is what we need. Nothing else.
    Albeit there may be joins in some cables.
     
  18. bmrpl

    bmrpl New Member

    Hi Mike83,

    Sorry for not responding any earlier but I only have Sundays to do anything. I'm on it now as we speak and I guess these cables are my live in and out to the boiler ☺️

    image.jpg

    If I use these two which would be my original 1 on the timer and the split black to my heat link to connect to the heat link and then use the split black to t1 and I identified the brown solid 3 from programmer going to no 3 in the stat - that would be my t2 ☺️

    Is that it??
     

    Attached Files:

  19. Mike83

    Mike83 Screwfix Select

    Down solid 3 from programmer shouldn't go to 3 on the stat. It should go to 1.

    Live out from boiler (grey) should go to 1 on programmer. This seems correct.
    3 on programmer should go to L on room stat.
    3 on room stat should then go back to boiler (live in).
     
  20. bmrpl

    bmrpl New Member

    Thanks Mike83,

    What I thought it was -

    I identified the T1 and T2 cables from heat link which is the split black and the former number 3 on the programmer (solid brown)
    I terminated and isolated the neutral and earth cables on the nest.


    Now the light grey will go to to 2 on heat link (it used to be 1 on the old programmer)
    And the second half of split cable will go to 3 on heat link.

    All neutrals apart from the isolated one will go to a block and neutrals in heat link.

    All live cables in a block and then to live on nest.

    All earths in a block and then to earth in heat link?

    Is that correct please? I really appreciate all your help ☺️
     

    Attached Files:

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