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Switching relay

materas
materas Member Posts: 2
edited March 22 in Gas Heating

I have an Greenstar combi 100 p / 151p zwb28-3a. … zwb42-3a. I have 2 circular zones.. Can I use the Taco SR502-4. And if so do use a jumper to the ZC ZR

KEITH

Comments

  • 109A_5
    109A_5 Member Posts: 2,285

    Not enough information, the Taco SR502-4 may not be 100 % compatible with an existing system.

    If nothing (jumper or other equipment) is connected to the ZC ZR terminals the circulators the SR502-4 is controlling will never run.

    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
    materas
  • HVACNUT
    HVACNUT Member Posts: 6,670

    The jumper should be factory installed, and you would leave it. XX dry contacts to the thermostat connection on the boiler.

  • hot_rod
    hot_rod Member Posts: 24,800

    Here is a wiring example with a Caleffi ZSR

    120V power, lower left

    thermostats on top

    XX to boiler contacts, usually a TT connection

    The newest version has a snap in removable 40Va transformer, circuit breaker protected

    Screenshot 2025-03-22 at 3.39.10 PM.png
    Screenshot 2025-03-22 at 3.38.55 PM.png
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • 109A_5
    109A_5 Member Posts: 2,285

    What if the proprietary OEM control equipment was used, just replacing the CZM100 with a switching relay may not be enough to restore proper operation. And the third party controls don't seem to control zoned circulators AND zone valves if both were used. Again not enough information was presented.

    image.png
    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 10,329

    I have an Greenstar combi 100 p / 151p zwb28-3a. … zwb42-3a.

    This is actually two different boilers. The manual has both models on the cover because it is for both boilers. Do you know which one you have? it will be on the rating plate with the serial number. It is a good thing to know for future reference.

    Edward Young Retired

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

  • materas
    materas Member Posts: 2

    thank you for your time on this. I’ll find out

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 10,329
    edited March 23

    @109A_5 has a good point about the third party control compared to the recommended control. This boiler has DHW priority built into the onboard computer software. The means the Domestic Hot Water for taking a shower will use the full capacity of the burners in order to make sure you have enough hot water while you are in the shower. The space heating (or central heating CH) will stop operating for the short time that you are using the hot water. The Taco Control may not communicate with the GreenStar and keep the circulators operating for the zones without regards to the DHW operation.

    I would look into the CZM100 control and see if that is reasonable priced compared to the Taco SR 502.

    Screenshot 2025-03-22 at 8.27.18 PM.png

    Here is the circulator 2 Zone option from the IO manual for your heater

    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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