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applying 24v to Tekmar 274

trl14 Member Posts: 5
I'm twining 2 utica UB-95s together.I'm using a Tekmar 274 to control  the boilers and provide outdoor reset.Tekmar wants 20v min. to the "boiler demand" terminals.  I have 2 t-stats going to a control box that looks home made and 1 going to a honewell r87 single pump control the  2 tt's are conncted to the 274 but I do not have 24v there just dry contacts. how can i tie a 24v transformer to my "endswitchs going to the tekmar control?



  • Randy Baerg
    Randy Baerg Member Posts: 26
    tekmar 274 boiler demand wiring

    To provide a 24V powered demand to the tekmar 274 do the following: Run two wires from your end switch (let's call it X1-X2) to the 274 enclosure. Connect one of these wires, let's say X2, to the 274 boiler demand terminal 22.  

    Now run two wires from your 24V transformer R & C to the 274 enclosure. Connect the C wire to the 274 boiler demand terminal 21. Connect the R wire to your end switch X1 wire with a wire nut.

    Now power the system and transformer up. You had it turned off right?:)

    Now whenever the end switch closes the 274 boiler demand will be energized and the control will start targeting based on Outdoor Air temperature. The Application drawing A274-5 shows something similar.

    The boiler T-T connections are wired to the tekmar boiler dry contacts. This should fire the boiler(s) when it closes. I hope this helps and have a Merry Christmas!
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