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pls help, swapping honeywell cm927 to geo cosy

Discussion in 'Plumbing and Central Heating' started by jakk81, 7 Jun 2017.

  1. jakk81

    jakk81

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    Hi wonder if anyone on here may help?
    im looking to swap my current Honeywell cm900 series (bdr91) thermostat.
    for a geo cosy thermostat,
    on the bdr91 it has - N L L / A B C connections
    on the cosy it has - N L E / T1- 2 CONNECTIONS AND T2 2 CONNECTIONS,
    the main wonder I have is that the bdr91 has 2 live connections ? the cosy has 1 ?
    any advice would be very helpful,
    I have a combi boiler.
     
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  3. stem

    stem

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    The two 'L' terminals in the BDR relay box are linked together internally, so are electrically connected anyway.

    The first 'L' terminal is used to accept the Live supply and the second 'L' terminal is there to provide a Live to the switching contacts if your boiler has 230V switching. (There will be a link wire between one of the 'L' terminals and the 'A' terminal if this is the case) Otherwise the switching contacts can be left 'potential free' for boilers that use switching voltages other than 230V

    You will have a wiring diagram provided with the Cosy Thermostat which will provide you with the information you need. Unfortunately I have only seen one once, and cannot remember the wiring details from memory.

    Edit:
    Just remembered that the Cosy is a bit of an unusual beast, in that the instructions describe wiring it into the existing controls (ie not replacing or removing them) This can be done in parallel or serial wiring and there is a switch provided by Cosy to select the method used. The instructions will explain.
     
    Last edited: 7 Jun 2017
  4. jakk81

    jakk81

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    thanks for your help does this help to guide me ?
     

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  5. stem

    stem

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    Not really, I understand the BDR and your picture of the manual shows lots of different systems, but how do I know which one is applicable to yours? Unfortunately not all combi's are wired as shown in the drawing labelled 'Combi'. A photo of the existing wiring at the BDR would help a bit more.
     
  6. jakk81

    jakk81

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    is this what you mean?
     

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  7. jakk81

    jakk81

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    bdr top right combi boiler thanks
     
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  9. stem

    stem

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    So are you are saying then that your BDR is wired exactly like this?

    relayboxdiagram.jpg
     
  10. jakk81

    jakk81

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    I will double check when I get home as i thought this would be the way its wired being a combi boiler?
    thx
     
  11. stem

    stem

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    But you never know, it might be ;)
     
  12. jakk81

    jakk81

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    Well yes it virtually as diagram but even better I only have one live, but the only last thing I'm unsure about is the jumper settings I'm unsure if its a single zone setup or a no existing thermostat ? Any thoughts? Thanks again
     
  13. stem

    stem

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    I'm not sure what you mean by this. Which Live is missing? The boiler and the BRD will both need a live.

    It should look something like this (Edit. With Cosy shown connected).

    Drawing1 Model (1).jpg

    If your set up is different, or you are unsure about anything, please post back and don't proceed. Or better still
    How many heating zones does your home have? If there is just one room thermostat controlling the heating in the whole house, then it's a single zone (wired to T1) if there are two room thermostats, for example, one for upstairs and one for downstairs then it's a dual zone. (wired to T1 & T2)

    If you have an existing thermostat then for some reason it should be retained (this is why I think the Cosy is is bit odd) I found a manual on line that looks the same as the one you are using that states.

    "Cosy is a smart thermostat and therefore will work with any heating system that uses or is capable of using a home thermostat. It works with an existing thermostat (if fitted) which should not be removed."

    The BRD is a thermostat receiver so, yes, you have a thermostat. Make sure that you follow the Cosy operating instructions carefully, especially.

    1. Set up Cosy
    • Set the existing heating controls to ALWAYS ON
    • Set the existing central heating thermostat to MAX
    • Press the middle button on the Cosy switch so that it is green
     
    Last edited: 8 Jun 2017
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