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Nest E thermostat wiring

So I have a nest e but I’m getting an error for the red wire not being connected. My current thermostat has a white, red, and blue. After checking the wiring downstairs I found the problem but wanted to get confirmation here first. The blue and red are tied together see pictures. Please advise on how I can get this right. 


  • Zman
    Zman Member Posts: 7,446
    The Colors are irrelevant, the electricity does not know the difference. Can you draw out which wires go where? What type of t-stat is pictured?
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • scuzz21
    scuzz21 Member Posts: 5
    It’s a basic Honeywell as seen below. The white is just 2 tied together to extend it and the blue/red are tied together to extend it too? The brown sheathed covered wires are going to the furnace and the white/blue are coming from thermostat upstairs.
  • Zman
    Zman Member Posts: 7,446
    The nest will want the R and W which are connected to the TT in your picture. It will also want a common wire. I am guessing that the 3rd wire is a common. I would double check before connecting.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,132
    You’re going to need a common. Is this a furnace or a boiler?
  • Big Ed_4
    Big Ed_4 Member Posts: 2,239
    Nest , slowly I turn ....step by step . :)

    The nest needs to be powered all the time , normal problem you need a third wire to hard wire a common . You have an option to pull it off the wall and charge it with that tripod adapter ..
    I have enough experience to know , that I dont know it all
  • Jamie Hall
    Jamie Hall Member Posts: 21,110
    As I read the directions for the Nest -- which, in my not at all humble opinion, are even worse than the thermostat itself -- you can use that blue wire as a common power source. Question is, where to hook it up. That controller on your system does not have a handy dandy common terminal. What it expects is a switch which closes the circuit between the two T terminals.

    I think that that switched circuit would be Rc and W on the Nest; thing is, the Nest is going to expect 24 vac between the common and Rc, and you may have to wander around in the basement to find a power source.

    Incidentally, I hope whoever did that wiring in the basement for the thermostat never returns. That's just... horrible.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England