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Taco sr503 relay question

Leon82Leon82 Member Posts: 632
I'm only using zone 1 and 2 and the tt contact goes to the first tt input on the boiler.

I want to move the 2nd zone to the priority zone 3 and use the priority tt to the second tt input on the boiler to run a separate odr/temp curve. But I want the priority function inactive

I read the directions a few times and am a little confused. Do both end switch close when the priority zone calls for heat? If so it is going to kill my plan



  • Dave H_2Dave H_2 Member Posts: 352
    It sounds like you have a SR503-EXP? Am i correct?

    The -EXP controllers have two separate end switches (XX). The "Main End Switch" only closes upon a heat call from any heating zone, in your case Zone 1 and Zone 2.

    The "Priority End Switch" only closes when Zone 3, the priority zone, is calling for heat as long as the priority switch is on.

    Dave H.
    Dave H
  • Leon82Leon82 Member Posts: 632
    Yes , exp.
  • Leon82Leon82 Member Posts: 632
    edited November 2017
    It looks like it won't work like I had hoped.

    I'm getting 7 volts across rw on a the zones NOT calling for heat. Is this normal?

    It is a battery thermostat with only 2 wires
  • HVACNUTHVACNUT Member Posts: 2,628
    When the thermostat is open, it should read 24v across TT for that zone because it's kind of a false reading as it's picking up voltage through the relay coil.
    When the thermostat is closed, it should read 0v across TT
  • Leon82Leon82 Member Posts: 632
    Ok, thanks. The one that's closed is at zero currently
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