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taco question

ableable Member Posts: 16
I have a question on wiring the sr 503. Boiler is weil mclain  3 section oil with tankless  coil 3 zones of heat domestic is still from the coil installed new relay sr 503 so circ wouldnt run  below low limit wired to  diagram in taco wiring diagram dated 2005 circs will still run below low limit if I remove wire from zr terminal it works right but then wont fire burner to limit called taco tech suport they told me it should work and that I had a wire wrong or a jumper left in went back and rechecked all wiring and it is per diagram and there is only one feed wire to boiler boiler had 2 sr 501 but werent wired through zc and zr originally any help would be greatly appreciated


  • Joe MattielloJoe Mattiello Member Posts: 589
    SR503 wiring using the alternative wiring diagram for tankless coil

    The instruction sheet attached will clear thing up for you.  It's a simplified diagram with ZR/X2 wired to ZR on the boiler aquastat, and ZC to ZC on the boiler.  This will prioritize the tankless coil which is the main reason to use this wiring method anyway.  As you may already know you can always fire the boiler using the low voltage thermostat terminals TT, but would not interrupt the 120 volts to the circulators when the boiler water temperature drops below the 140 degrees threshold.  Hopefully this clears up the ambiguity. 
    Joe Mattiello
    N. E. Regional Manger, Commercial Products
    Taco Comfort Solutions
  • ableable Member Posts: 16

    thanks for the help  thats how I have it wired and it does  not work circs still run below low limit setting and  aqua stat on boiler does not operate all jumpers are in where there suposed to be  and there is only one hot leg feeding boiler also L1 is the hot leg not the nuetral polarity is not reversed   if i remove wirefrom zr circs stop but boiler only operates when it gets below limit I called taco and have to call them from the job next week thanks again for the help also swaped 8124 a relay with one on the truck and no change so it not that
  • Paul48Paul48 Member Posts: 4,492

    allowing for the 10 degree differential below the low limit? It makes sense that disconnecting "zr" makes the boiler behave that way.It's the feed from the 503 to the burner, so without it the burner is controlled by the aquastat. Disconnecting it should have no affect on the circulator. "ZC" feeds the circulator by way of the low limit.
  • ableable Member Posts: 16
    still confused

    I  understand what zr and zc are suposed to do. Why with zr tied in does circ still run when boiler temp is below  low limit   I can turn low limit all the way up and it will have no effect  power is backfeeding from zr to terminal 4 and powering the circs
  • icesailoricesailor Member Posts: 7,265
    Missing proper control?

    I think you may have an improper or missing control in the loop.

    Or you don't understand how it is supposed to work.

    With a "triple acting control" with a Low Limit/Circulator control in the loop, the low limit is the operating control and maintains boiler temperature at all times at what ever you set the setting at. Say 150 degrees. The boiler will always maintain a temperature of somewhere around 150 degrees. When the thermostat calls, it over rides the operating control and flips the control up to the High Limit. Say, 180 degrees. The burner is now supposed to run until it explodes the boiler, the heat call ends, or the high limit is reached. And the circulator is also powered through the thermostat call. But, it is also wired through the low limit. If the boiler temperature drops below the set point (150 degrees), it stops the circulator. Until the boiler catches up with the temperature. Zone Control or Zone Relay ( I can never remember which) is broken when the circulator call to stop is supposed to stop the relay from allowing the circulators to run when the boiler is below the operating set point. The burner should NEVER stop. If the burner is stopping when you turn the operating control down, the wiring is incorrect.

    I recently found a control with the yellow wire that normally feeds the one circulator being used to power a SR 503. It had issues. It worked to the satisfaction of the person who wired it when they left, but is wasn't correct.

    The ZC/ZR connections are the most mis-understood  in heating control and wiring.
  • Paul48Paul48 Member Posts: 4,492

    correct polarity and function of the aquastat using the Honeywell schematic If that is correct, and you have everything wired correctly to the 503, there is a problem with the 503. Just to clarify, you are using L1 and L2 from the aquastat to power the 503, correct?
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