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Thread: Connecting a Nest to a 3 wire thermostat

  1. #1
    Junior Member

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    Question Connecting a Nest to a 3 wire thermostat

    Having a real hard time trying to find anything related to a 3-wire thermostat wiring setup. I just removed my ANCIENT Honeywell mercury-laden thermostat to discover that I have 3 wires coming out of my wall I would have written down what they were connected to on the Honeywell, but much like everything else in my ancient house there was nothing that seemed to be able to discern a difference as to where they were screwed in. Anyway, I have:
    1 - Red sleeved wire
    1 - White-ish sleeved wire
    1 - Blue-ish sleeved wire

    I have a Nest that I just bought today that I wanted to install, but so far I'm not even going to attempt the hookup until someone can give me a little better idea of what to connect to where! My cooling system is entirely separate from my heating system, which is done via natural gas boiler. I have radiated heat throughout the house, one zone for upstairs and downstairs, thermostat is located downstairs.

    Any help would be MUCH appreciated! Trying to get this done before the wife gets home.
    -Ellis

  2. #2
    Junior Member

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    Is the Boiler in a place to look at and see what the wires are attached to at that end. That might give you an idea of where they need to go on the NEST.

  3. #3
    HVAC Thermostat Specialist

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    Quote Originally Posted by EllisB View Post
    1 - Red sleeved wire
    1 - White-ish sleeved wire
    1 - Blue-ish sleeved wire
    The wire colors alone will not help. Depending on who wired the thermostat you never know what colors they used. Can you provide a picture of your existing thermostat terminals and where the wires were landed?

  4. #4
    HVAC Thermostat Specialist

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    Does one thermostat control both systems?


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