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Heat intermittently not shutting off Nest 3 and Taco SR504
awoz
Member Posts: 4
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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Comments
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You need the hard common , Three 18 wires needed...To work
There was an error rendering this rich post.
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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?
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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?
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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?0
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This is current set up
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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/0 -
@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 401-942-80001 -
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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?
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Resistor always goes across the W-C ( com ) terminals.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?1 -
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