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Taco 007 circulator not working

razzor Member Posts: 20
I have a zone in my hot water baseboard system that doesn’t heat up. The circulator pump didn’t seem to be working so I replaced it. Still no heat to that zone. The Taco SR503 Switch Relay light for that zone comes on when thermostat is calling for heat but don’t hear the circulator pump running. Thoughts or ideas?



  • Zman
    Zman Member Posts: 7,574
    A multimeter to check that you have ~120 volts to the circ would be a good start. I found this app the other day but have not had a chance to use it. https://www.danfoss.com/en-us/service-and-support/downloads/dcs/magnetic-tool/#tab-overview
    It should verify rotation.
    If you have power and rotation, you must be air locked.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • razzor
    razzor Member Posts: 20
    Thanks Zman. So the thermostat is working since the zone light comes on. I thought maybe the circulator was bad so replaced it. Still not working. Worked fine up until it didn’t! Not sure what would cause power not to get to circulator.
  • mattmia2
    mattmia2 Member Posts: 9,738
    the relay could be bad or bad wiring or connections. have to trace it back with a meter
  • JohnNY
    JohnNY Member Posts: 3,231
    razzor said:

    So the thermostat is working since the zone light comes on.

    The zone light tells you the relay has power to the coil but nothing else. You'll still need to verify you've got power to the pump terminals.

    Contact John "JohnNY" Cataneo, NYC Master Plumber, Lic 1784
    Consulting & Troubleshooting
    Heating in NYC or NJ.
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,646
    If you find that you indeed do not have power (120 volts AC) to the pump, there is a fuse in the SR50#. If your old pump shorted out it may have blown the fuse.
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
    HVACNUT Member Posts: 5,861
    If you have the older style SR503 with the cube relays, you can try swapping it out with a cube from another zone. If not, put the thermostat and circulator wires on a different zone in the SR503 and see if that works. Remove the original wires for that zone first of course.