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Honeywell t9 thermostat help

Ghynes440
Ghynes440 Member Posts: 53
in Gas Heating

I recently got a Weil McLain gv90+5 gas boiler installed. We converted from oil. I just ran a new cable and bought the Honeywell for it. But the wiring diagram is rather vague on Weil McLain. The old thermostat was wired to the T stat wiring harness.


With the new cable I connected the red and white to the t-stat harness and then connected c wire to the c harness. The thermostat does not turn on. Did I miss something?

IMG_3596.jpeg IMG_3601.jpeg

Comments

  • ratio
    ratio Member Posts: 4,149

    Do you have 24 VAC between R & C? Maybe a fuse was blown during installation.

  • pecmsg
    pecmsg Member Posts: 6,582

    blew the fuse or the transformer.

  • pecmsg
    pecmsg Member Posts: 6,582

    we also need pictures of the other end connections.

  • HVACNUT
    HVACNUT Member Posts: 7,081

    If all above is good, then switch the Red and White wires

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 18,830

    Connect R on the thermostat (using the red wire) to the red terminal on the boiler.

    Connect C on the thermostat (using the yellow wire) to the "C" Common terminal on the boiler

    Connect W on the thermostat (using the white wire) to one of the black thermostat wires at the boiler. Which one?? The one that does NOT have 24volts between it and common with the power on.

    Weil Mclain should identify those two black wires as R & W but apparently, they don't

  • Ghynes440
    Ghynes440 Member Posts: 53
    https://forum.heatinghelp.com/discussion/comment/1867086#Comment_1867086

    thank you! I will try that. There is also some relay box with a white/yellow and a white/blue.

    The old thermostat was wired using that box along with a c wire. It was an old thermostat.

    IMG_A98758B2-ED28-4AD3-8E80-00B183AE8207.jpeg

    any idea what box this is?

  • ratio
    ratio Member Posts: 4,149

    That is a RIBU1C, a "Relay In a Box". It's used as an interposing relay to isolate equipment electrically so the various transformers don't interact poorly; or to switch a line voltage load from a 24 volt source (thermostat).

    The white/yellow and white/blue are the control wires, applying 24 VAC to them will close the relay (yellow, orange, & blue wires) and activate the load it's connected to.

  • 109A_5
    109A_5 Member Posts: 3,048

    If the old thermostat controlled the relay box then the relay box controls the boiler. If that is the case the orientation of the two black wires from the boiler is irrelevant.

    The thermostat should get its power from an independent transformer, not the boiler's transformer.

    As @ratio stated, the white/yellow and white/blue are the control wires they should go to the independent transformer and the thermostat. The relay's Yellow and Orange should go to the boiler's two black wires.

    image.png
    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System

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