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Heat intermittently not shutting off Nest 3 and Taco SR504

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awoz
awoz Member Posts: 4
in Thermostats and Controls
Went from a basic Honeywell 2 wire Tstat to a Nest 3 learning thermostat. Installed the resistor that came/ unit from the white on SR to the common. This radiant zone worked fine for the first 2 weeks. Last week it was hot in room, nest showed setting to 68, but the actual temp was 76. Tried shutting down power, turned back on- everything was fine. Then it happened again today: 68 on tstat ( not showing orange which it does when calling for heat at t stat, and no light on Zone indicating calling for heat, ),but room was 75 and taco pump was still circulating water. Net- although the tstat & SR indicating no light. Heat continues. Any ideas on what could be causing this?

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  • Big Ed_4
    Big Ed_4 Member Posts: 2,798
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    You need the hard common , Three 18 wires needed...To work

    There was an error rendering this rich post.

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,945
    edited February 6
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    If the light on the SR 504 for that zone shows there is no call for heat, then the circulator pump for that zone should no operate. Can you check to see if the pump that is wired to that zone is operating? Check the voltage at the H to N with a volt meter at the control. You should get 0 volts with no call for heat. If you are getting 120VAC there, then you have an issue with the TACO SR504.


    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,945
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    It can work with the resister in many cases, but on the Taco SR504 you may need a different value resister. @SteveSan would know that answer. If you can do what @Big Ed_4 suggests, then your problem will go away.


    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

    SteveSan
  • awoz
    awoz Member Posts: 4
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    Just tested and no power on the Zone (1). As i mentioned, I shut all power off earlier and 1st time it happened. Certainly if it happens again, before i shut power, will check voltage. See picture- but I only have Red/White on SR for zone - but I do have a 3rd wire running from tStat I could hook up and use, then go right to the shared common (where resisstor is currently going- that lines up with the diagram above). Your suggesting thats the better way vs. 100ohn 0.5watt resistor?
  • awoz
    awoz Member Posts: 4
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    This is current set up


  • HotRodder63
    HotRodder63 Member Posts: 1
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    definitely want to check voltage. common issue with the nest Mosfet failure. Get with Nest and warranty it out!
    https://www.reddit.com/r/Nest/comments/5l1c53/nest_failed_with_heat_on_for_the_third_time/
  • SteveSan
    SteveSan Member Posts: 235
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    @awoz How many Nest are you using on your SR504-4? Our resistor won't work with the Nest. They suggest a 220ohm and up to 5watt for a Nest.

    Also, appears the brown wire is going to the 24vac side. If that is part of the resistor, it would go across the W and Com side of the two terminal plug.

    If you have any questions, please give Taco Technical Services a call during normal business hours Mon-Fri 8am-5pm EST 401-942-8000
    Dave H_2
  • pecmsg
    pecmsg Member Posts: 4,875
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    Always the N E S T !
    GGrossEdTheHeaterMan
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,945
    edited February 6
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    Is the resistor connected from W to 24VAC? Should it not be connected from W to COM?
    I'm not sure, Just asking?

    And where is the RED jacketed wire connected to 24 VAC and COM heading to? I wonder if you are over taxing the SR 504's transformer?

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • SteveSan
    SteveSan Member Posts: 235
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    EdTheHeaterMan said:

    Is the resistor connected from W to 24VAC? Should it not be connected from W to COM?
    I'm not sure, Just asking?

    And where is the RED jacketed wire connected to 24 VAC and COM heading to? I wonder if you are over taxing the SR 504's transformer?

    Resistor always goes across the W-C ( com ) terminals.
    HVACNUT
  • HVACNUT
    HVACNUT Member Posts: 5,844
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    SteveSan said:
    Resistor always goes across the W-C ( com ) terminals.
    And yet the Nest was so smart it worked anyway... for a little while. 
  • awoz
    awoz Member Posts: 4
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    Changed resistor to 220ohm and changed out Nest base, switched resistor to com vs 24vac. So far so good. Thanks for the advice!!
    Dave H_2

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