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Tekmar 351 to a Tekmar 356

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Signgirl
Signgirl Member Posts: 6
in Thermostats and Controls
My replacement control, the Tekmar 356 is wired like the old 351 except for one slot. It is labeled "T", the mix demand signal. .  The instructions say it must have an electrical closure with the terminal labeled c-. How do I arrange that?

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  • Ironman
    Ironman Member Posts: 7,376
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    Tekmar labels “R” and “C” backward from the way thermostats are labeled.

    Simply put, “R” takes  power directly from one side of your 24v transformer to the 356. “C” takes power from the other side of the transformer, through the thermostat or zone control, then to “T” on the 356.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
    STEVEusaPA
  • Signgirl
    Signgirl Member Posts: 6
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    So, it is wired properly leaving the t slot without a wire? The new control also came with a ground wire on the 120 side, and the older one did not. Does that ground have to be connected for the control to demand for heat? The control is on, but not demanding for heat.
  • Signgirl
    Signgirl Member Posts: 6
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    old and new

  • Zman
    Zman Member Posts: 7,569
    edited March 2021
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    The 356 will not work without a wire on the "T".
    You wire the transformer to 8 and 9. The thermostat "R" wire also wires to 7, the "W" wire coming back from the t-stat wires to 9.
    The ground coming out the back wires to the ground wire on the 120 volt circuit to the circulator.
    I would also suggest cleaning up the low voltage wiring and only stripping enough insulator to make contact on the terminal. The extra copper you have showing could easily short out and let the smoke out of the controller or transformer.

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    Signgirl
  • Signgirl
    Signgirl Member Posts: 6
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    Thank you very much for your reply. So then which wire was coming back to the thermostat on the old one as there wasn't a space for it?  
  • Signgirl
    Signgirl Member Posts: 6
    edited March 2021
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    I may not have asked that very well. On the old thermostat they were only four wires going to that side. There isn't a fifth  wire for the T terminal. On the other hand, there are two unused wire in the back of the box, a red and a white. But those were not connected to the old control.
  • Zman
    Zman Member Posts: 7,569
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    I don't have a wiring diagram for your old unit and wire colors don't mean a whole lot (electricity is color blind).
    If you can figure out where the wire go to and from, the wiring diagram for the 356 is pretty straight forward.
    If the black and blue go to the boiler they belong on 5 and 6. From there you need to figure out the transformer and the t-stat. Pictures might help...
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Mike_Breault
    Mike_Breault Member Posts: 35
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    @Signgirl the " Heat/ Heat" terminals on the 351 are a dry contactand likely went to the heat source / zone vlave.R and C are 24V power to the control..If you didnt have a heat demand controlled by a switch Jumper terminal 9-7 to create a demand.

    Call us if you need more help

    Mike B (tekmar)
    Zman

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