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Replace Honeywell CM907 with a Nest Thermostat

Discussion in 'Plumbing and Central Heating' started by Nicholas Lea, 27 Oct 2019.

  1. Nicholas Lea

    Nicholas Lea

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    Hi,

    I'm looking to replace my Honeywell CM907 thermostat with a Nest Thermostat.

    I'm happy to get someone in to do it but if it's simple enough the I'll do it myself.

    So, I've read the guide online (it's not been delivered yet) and I'm a little confused. Do I just need to wire in the Heatlink where the current thermostat is? Using the two wires as in the linked image of my current thermostat. The wiring guide for the Heatlink show a lot more wires so I feel like I'm likely missing a step if I'm only seeing the two wires with my current set up.

    http://imgur.com/a/JepkcNB

    Thanks.
     
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  3. flameport

    flameport

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    How it's connected depends on what heating system you have.
    The Nest heatlink requires a 230V power supply and at least one extra wire for the switching, so it will not just fit where the existing thermostat is .
     
  4. Nicholas Lea

    Nicholas Lea

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    Thank you,

    We have an Ideal Standard Logic Code Combi 33 Boiler
     
  5. muggles

    muggles

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    Ah, in that case call someone in to do it, and ask them to connect the OpenTherm terminals. This will make your boiler more efficient, but requires the boiler casing to be removed, which is something that should only be done by a Gas Safe Registered Engineer
     
  6. ericmark

    ericmark

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    I think you are looking at Nest e to replace that thermostat, Nest e is battery powered, however as muggles says, if boiler has OpenTherm may as well use it, Nest e will also work with Opentherm.
     
  7. stem

    stem

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    If you have purchased the Nest with the mains powered Heat link and want to diy it can be done without opening up the boiler.

    The brown wire in the existing thermostat A, connects to the Nest Heat link terminal (2) Heating - Common

    The black wire with the brown sleeve in the existing thermostat B, connects to the Nest Heat link terminal (3) Heating - Call for Heat

    The Heat link also requires a 230V mains supply, which comes via the same 3A fused spur that isolates the boiler. So, if you wire the Heat link L, N & E directly to the 'load' side of the fused connection unit, you won't have to open the boiler casing.

    The Nest thermostat requires a 12v supply which it can get by being wired directly to Heat link terminals T1 & T2, or by using a separate plug in power supply.

    If you have purchased Nest E, which is battery operated, then you don't need the mains supply so it's a simple swap

    Connect the brown wire in the existing thermostat A to the Nest E terminal (C) 'Common'

    Connect the black wire with the brown sleeve in the existing thermostat B to the Nest E terminal (NO) 'Normally Open'

    If you want to use opentherm @muggles has advised you how to do this
     
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