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Strange relay behavior

Are you trying to say the action seems backwards? That's how your description sounds to me? Red light should mean that the heat's on, is that what you're saying? Could the relay actually be a normally-closed?


  • Dave_4
    Dave_4 Member Posts: 1,405
    Strange relay behavior...

    I have a Taco SR501. I want to use the call for heat from the thermostat to close the normally open connection to trigger the boiler. I have connected 120VAC to the line input, removed the jumper, and connected the thermostat RH and W to the R and W inputs on the SR501.

    When I apply power to the relay and there is NO call for heat, the red light is on and the relay is closed. When there is a call for heat, the red light goes off and the relay opens. Anybody know why?

    Sign me,

  • Dave_4
    Dave_4 Member Posts: 1,405

    It seems backwards. Although, if the thermostat wires are not at all connected, I just get the green light.

    Not connected: Green
    Connected, no call for heat: Green and Red
    Connected, call for heat: Green
  • Dave_4
    Dave_4 Member Posts: 1,405
    Measured the thermostat leads...

    Instead of an open cicuit, I get about 75ohms when there's no call for heat. If I measure voltage, I get some millivoltage. Does it sound like the thermostat might be bad?
  • Dave_4
    Dave_4 Member Posts: 1,405
    My bad...

    thermostat that is. I happened to have an identical Lux500 that was not in use, and I swapped the "faces". Looks like the thermostat was bad. Now it seems to be working.

    Nothing like a second set of eyes to help me find the problem. ;-)

  • Dave_4
    Dave_4 Member Posts: 1,405
    Here's what I don't understand...

    Can the SR501 relay be used with a 24V input to trigger the relay? Or will it only work with an essentially dry contact?
  • Joe Mattiello_2
    Joe Mattiello_2 Member Posts: 94
    Transformers do hold black smoke

    The SR board or any Taco control only works with a dry contact or continuity, closure of a switch. There is 15 VA transformer to pull in the relays, and power thermostats, should you need to. Putting a 24v signal to TT on the board will cause the transformer to let out some of that black smoke we tried so hard to contain.
    Joe Mattiello
    Technical Support Technician
    Tel. 401-942-8000 X 484
    Fax. 401-942-2360
    1160 Cranston St
    Cranston, RI 02920
    [email protected]
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