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Replacing Honeywell CM927 with Nest Heatlink

Discussion in 'Plumbing and Central Heating' started by dwag, 6 Jan 2016.

  1. dwag

    dwag

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    I'm interested in purchasing a 3rd Gen Nest (UK) though don't really have much knowledge about wiring the Nest Heat Link to the boiler.

    The Nest would be replacing a Honeywell CM927 Wireless Thermostat, the relay box BDR91.

    I have a Bosch Worchester Greenstar 28i Combi Boiler (if that helps?)

    The actual Nest wireless thermostat would be placed on the stand, or just connected via the USB plug. I would just need to replace the Honeywell relay box to the Heat Link, though again, have no knowledge of wiring these things.

    I've taken a photo of the existing wiring from the boiler to the Honeywell relay box, I was just wondering if it'll be a very simple switch over to the Heat Link, that I could perhaps do myself, rather than call someone out for £70 (if its a simple thing)

    If anyone could assist and let me know if it's do-able for a capable but novice person and what the Honeywell wiring on the relay box be to the Heat Link, I.E, Honeywell A is 1/2/3? on the Heat Link.

    Many thanks!

    Relay Box diagram (Borrowed from another thread :) ): http://s999.photobucket.com/user/zarch1972/media/CM900.jpg.html

    Dropbox link to relax box photo: Dropbox - IMG_20160106_130923.jpg

    Nest Installing Diagram: http://prntscr.com/9mrvc4
     
    Last edited: 6 Jan 2016
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  3. stem

    stem

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    Yours looks like of of the simplest nest wiring upgrades possible. The L & N wires at the BDR 91 would go to the L & N at the nest heatlink, and if the wires presently in A & B at the BDR 91 are connected to Ls and Lr at your boiler, then they would go to 2 and 3 at the heatlink.
     
    Last edited: 6 Jan 2016
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  4. dwag

    dwag

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    Thanks for your reply!
    Just to clear things up, what you're suggesting is that A = 2 and B = 3 on the heatlink?
     
  5. stem

    stem

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    It doesn't really matter with your installation. Because the C (BDR91) and 1 (heatlink) terminals are not used, it will work either way around.

    However, if you want to keep to the usual wiring norm, then it's how the heatlink connects to the boiler that is significant. So the wire at the BDR91 that is currently connected to the boiler Ls (Live Supply) would go to 2 on the heatlink, and the wire that goes to the boiler Lr (Live return) would go to 3 at the heatlink.
     
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  6. incrediblechunk

    incrediblechunk

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    I have read through this post with interest. I also have a Honeywell system (although the HC60NG relay / Y6630D wireless thermostat instead of the BDR91/CM927, but the wiring within the relay is labelled the same with the same connections as described above). Presuming I can simply swap the wires as noted, the question I have is my system has a programmer that it separate to the relay / thermostat, I've read somewhere that you simply keep this permanently switched on but wondered if anyone could confirm this please?
     
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  8. stem

    stem

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    Hi incrediblechunk.

    First of all, you should have really started a new thread. Asking your question in someone else's is known as Hijacking and against the forum rules. However, as I see that you are new to the forum, I will answer your question, and you will know for next time.

    The Y6630D is a wireless thermostat and as such only controls the room temperature, so you will need to use your separate programmer to provide the on and off times.

    You are getting confused with a wireless programmer which is a different beast. They incorporate the room temperature and also the on/off time functions. If you install a wireless programmer, then you would need to let that control the temperature and also the on/off times and leave the separate programmer switched permanently on.
     
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  9. incrediblechunk

    incrediblechunk

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    Stem

    Thanks for your answer. I had messaged the original poster and asked if he was OK me hijacking the thread and he encouraged me to in case he learned anything new, but point noted for future posts.

    I realise the difference between the wireless programmer and thermostat, but the wiring within the relay unit seems to be identical in both systems so I was interested in knowing if there was a way to add the 3rd generation nest (as you would if replacing the wireless programmer) and then over rule the existing programmer with the nest, leaving the programmer permanently on. I've kept on researching and realise I will have to do some amendments to the junction box so that the hot water is controlled also but I haven't quite got there yet with that so will take your advice and start a new thread to see if anyone can help with the rewiring of that.

    Thanks again
     
  10. Agile

    Agile

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    You don't say what kind of boiler you have.

    But if a combi like the OP then you hardly need to have a 3G Nest.

    There are some small improvements but the main advantage is that they can control hot water as well. But that is not used on a combi boiler.

    These kind of aspects are why a new poster should start his own new thread.

    Tony
     
  11. incrediblechunk

    incrediblechunk

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    Thanks Tony. I will start a new thread. I was trying to minimise people's input but have complicated things it seems. Lesson learned.
     
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