From Honeywell wireless ST9100C to 3 wire thermostat

Discussion in 'Engineers' Talk' started by Botyo, Nov 21, 2018.

  1. Botyo

    Botyo New Member

    Hello :) I need help on wiring 3 wire thermostat currently i am with Honeywell ST9100C programmable thermostat and it works when it wants... Sometimes starting the boiler sometimes not so i decided to back on the old fashion one that i had long time ago an never got any problems and another plus will be less wi fi radiation at home :D Here are the pictures on my current wiring on the relay box and the new thermostat. My guess on the new wiring is: N Blue wire - Neutral, 1 Live - Brown, the question is what will be on 2 Grey or Black wire.. . that is my confusion please help if you know, thank you :) There is no info that comes with that new oldie.
    DSCF3555e.JPG DSCF3565e.JPG DSCF3560e.JPG DSCF3555e.JPG DSCF3560e.JPG DSCF3565e.JPG
  2. I'm attaching a diagram that might help you.

    I agree you put the blue into the innermost (N) and the brown in the (1).

    Looking at the attached diagram your grey wire is your boiler live and the black is the boiler neutral (assuming it was wired up correctly in the first place).

    I would then put the grey (live) into (2) and the black (neutral) into the outermost (N).

    I'm not an electrician but now you have the diagram I reckon you'll draw the same conclusion.

    Attached Files:

  3. Mike83

    Mike83 Well-Known Member

    The black and grey are live in and live out.
    Not neutral.
  4. That's like saying the blue wire in a plug is live out.

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