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Mgb 095k thermostat wiring

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tomf1035
tomf1035 Member Posts: 3
Trying to wire a utica mgb95 the diagram calls for c, tw, and tr thermostat wires i can find no reference to which wire is which. Also my thermostat only has two wires.  Any help?

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  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,746
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    If your thermostat has only 2 wires and doesn't need a "C"-Common' wire on the thermostat end you should have a wire on R or Rh and the other wire on W.

    On the boiler end one wire should go to TW & the other one to TR . But don't forget your limit controls and safety controls may need to be in that circuit.

    Follow the MFG wiring diagram & make sure all the limits and safety's work.

    Is this a new install??
  • Jamie Hall
    Jamie Hall Member Posts: 23,543
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    The manual for your boiler -- there are about 10 different variations -- will have the correct wiring diagram. Usually the only two wires you need are tw and tr, and if it is a two wire thermostat, it doesn't matter which is which. If it is a fancy three wire thermostat, you will have to locate a common for the c wire on the boiler somewhere.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • tomf1035
    tomf1035 Member Posts: 3
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    It is a new install. The boiler has a spot for a c wire so does the thermostat but your saying i probably don't need it?
  • tomf1035
    tomf1035 Member Posts: 3
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    Do you think i could just tie the tw and tr together and control the heat with the zone valve?
  • Zman
    Zman Member Posts: 7,588
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    Are you saying you only have 2 wires running from the t-stat and boiler but your thermostat has 3 terminals?
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Jamie Hall
    Jamie Hall Member Posts: 23,543
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    At a guess, if you tie TR and TW together the boiler will never shut off. You will have no control at all.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Ironman
    Ironman Member Posts: 7,385
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    What zone valve do you have? You make it sound as though there’s only one. Is that correct?
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,153
    edited November 2021
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    I believe that you are looking at this diagram @tomf1035



    I can see the C TR and TW indicated on the thermostat in the upper left of the diagram. (outlined in red)

    This is how you would connect a 2 wire thermostat


    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?