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Nest and Baxi boiler with two-wire thermostat

Discussion in 'Plumbing and Central Heating' started by nestrequest, 18 Jul 2018.

  1. nestrequest

    nestrequest

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    Hello - I'm a newbie on the site, and I've seen that folk are pretty helpful so thought I'd make my first post.

    I bought a Nest 3G thermostat and am looking to have it installed. I'm getting quotes for £100 locally and want to see if I can do it myself first. I have already taken a look at this post - https://www.diynot.com/diy/threads/nest-thermostat-and-baxi-combi-105e.416527/, but I still have questions.

    Attached are images of the images from the boiler (Baxi Duo-tec 40 GA) terminal block, the terminal block label and the existing thermostat with the cover off. The boiler instructions are here - https://www.baxi.co.uk/-/media/webs...hash=A633BF08B8BBF0129244373B3549B53390BA83F7

    I can see inside the boiler that I have both the L+N cables (for power) and the 1+2 cables (for switching), however when looking at my existing thermostat, there are only two wires inside it (brown and black which I assume to be L+N, or possibly L+SL? - this i not helped by the codes in the thermostat IMG_20180718_154434.jpg IMG_20180718_154539.jpg IMG_20180718_154434.jpg IMG_20180718_154539.jpg IMG_20180718_162156.jpg IMG_20180718_154434.jpg IMG_20180718_154539.jpg IMG_20180718_162156.jpg ).

    What I'm really puzzled at is why there is no call for heat cable at the existing thermostat that can go in the Nest terminal 3 (with a jumper from the live to 2). Is this a switched system? And if I wired accordingly to the Switched Live diagram in the Nest book, will the Heat Link/boiler blow if I am wrong?

    If this is a standard 230V combi wiring I have ready that I should wire up and connect the Heat Link inside the boiler (using additional wires from the L, N, 1 + 2) but surely this shouldn't be inside the boiler and I can't see how the wires would come out of the terminal block. Equally the condensing combi boiler is fully sealed so I don't see how I can get wires out of the boiler unit.

    So does anyone have experience of this set-up (and what set up is it) and how do I go about resolving this? Any thoughts gratefully received.
     
  2. muggles

    muggles

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    You shouldn't be removing the front casing of your boiler unless you're Gas Safe Registered, as it forms the safety room seal of your boiler, and the regulatory 26.9 checks need to be carried out before the boiler is used again once the casing has been removed.
     
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  4. Hazeldp

    Hazeldp

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    Following as I have exactly the same boiler wiring set up ... hopefully someone will respond with a solution !
     
  5. muggles

    muggles

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    The solution is to call someone who is qualified to remove the case to the boiler, and carry out the 26.9 checks on completion, IE a Gas Safe Registered Engineer. You won't get advice on how to DIY things which are the provision of GSRs on this forum I'm afraid - it's a safety issue
     
  6. DIYnot Local

    DIYnot Local

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