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Grundfos relay not working

REKBDR
REKBDR Member Posts: 41
in Thermostats and Controls

I have a Grundfos UPZCP-1 that is not energizing the AC power to the circulating pumps in my radiant heat floor. It is getting power (its red lights go on and off when I toggle the switch that is upstream on the power line). The thermostat is working because the zone valve which the relay controls is properly operating when there is a call for heat. The fuses inside look okay.

I suspect that the AC relay isn’t operating, whereas the relay for low voltage is. But I’m not sure I fully understand how the innards really work. Does the AC transformer inside provide power to the thermostat and to the red lights in the box and also to activate the relay to let AC power flow to the pumps? That would tell me the transformer is okay, no? Could this be a case of bad contacts in the high voltage circuitry? Fixable? Am I correct that the transformer at the boiler, powering the zone valve, has nothing to do with the relay control?

Sellers say this product was discontinued about a year ago. Does anyone know why?

Comments

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 10,068

    "The fuses inside look okay." My 1923 Model T Ford "LOOKS OK" but it has not run in over a year. You need to test those fuses to KNOW they are OK.

    "Sellers say this product was discontinued about a year ago. Does anyone know why?" Not enough people purchasing them would be my guess. The Taco SR501 and the Honeywell (Resideo) R845A were around for a lot longer and do the job just fine.

    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: 10,068
    edited February 13

    Try this control Taco SR501-4. This most matches the Grundfos.

    here is what the diagram looks like:

    Screenshot 2025-02-13 at 12.13.48 PM.png

    the Honeywell has been around a lot longer and this is what it looks like inside

    Screenshot 2025-02-13 at 12.16.04 PM.png

    And I cant be 100% sure but this is what I believe is happening inside your Grundfos control

    Screenshot 2025-02-13 at 12.18.29 PM.png

    Hope this helps.

    Edward Young Retired

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

  • hot_rod
    hot_rod Member Posts: 24,319

    A zone valve control?

    the yellow disc next to the transformer is a self reset fuse, if you have 24 v it is okay

    Do you have 120v at the pump connection?

    You need a volt meter to test it

    https://s3.amazonaws.com/s3.supplyhouse.com/product_files/Caleffi-ZVR104-User%20Guide.pdf

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • mattmia2
    mattmia2 Member Posts: 11,601

    where did you get this from? maybe it was sitting around because someone fried the contacts in the relay.

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 10,068
    edited February 14

    it is a single zone pump control like the SR 501

    Grundfos Discontinued Control

    Screenshot 2025-02-13 at 9.48.19 PM.png

    Edward Young Retired

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

  • 109A_5
    109A_5 Member Posts: 2,094
    image.png
    image.png
    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
  • REKBDR
    REKBDR Member Posts: 41

    Thanks. To get the heat back on, I just replaced it with with a sr501.

    EdTheHeaterMan

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