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What to do before replacing circulating pump? FIXED!!! (just a bad connection or two)

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Steve27
Steve27 Member Posts: 12
edited December 2022 in Oil Heating
First a little background, my oil fired boiler appears to be working fine. The upstairs is warm due to a separate zone/circulating pump. However the downstairs is cold, and it appears to be due to the circulating pump not running. I played with the thermostat, but I don't believe that's the issue. Should I open the electrical connection at the pump and test for line voltage? I see electrical components attached to the pump, can these be changed-out separately as opposed to changing out the whole pump? It's an Armstrong Model S-15 Serial 7911 unit (see images).





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  • mattmia2
    mattmia2 Member Posts: 9,734
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    Check for 120v to the circulator when it is calling. If there is no power to it then you have to troubleshoot that. It looks like the circulator has a capacitor, it could be bad but bad bearings are more likely. You can also try turning the impeller, it could just be stuck. It is probably time to replace it with a modern ECM pump if it has power and nudging the rotor doesn't get it working.
  • Alan (California Radiant) Forbes
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    If your pump is getting voltage and not spinning, it usually gets very hot. But yes, see if the pump is getting power. If no power there, it might be a problem with the relay or signal sending power to the pump.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • Jamie Hall
    Jamie Hall Member Posts: 23,419
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    Do you have a non-contact voltage tester? Big box stores have them, and they're cheap. If you have one, simply check to see if you are getting power to the pump at all. Don't have to undo anything.

    If you are, there may be a problem with the pump -- but if not, trace back to see where the pump power comes from. Probably a relay box or control box.

    Then go to the thermostat and make sure it really is working -- if it uses batteries, are they fresh (I know it sounds stupid, but we've all done that at least once).

    Go back to the relay or control box you found, and find where the wires from that thermostat are attached (usually the red and white ones). Measure the voltage across the two terminals. If the thermostat is calling for heat, it should be zero volts, or very close (that's between the two terminals, not from a terminal to ground). If it isn't zero, there is a problem either in the thermostat or the wiring from the thermostat to the control.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Dave Carpentier
    Dave Carpentier Member Posts: 594
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    Long shot, and you may have tried it already, but how about turning that speed dial back and forth ? Could a speed adjustment contact be arc-dirtied ?

    30+ yrs in telecom outside plant.
    Currently in building maintenance.
  • Steve27
    Steve27 Member Posts: 12
    edited December 2022
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    So I went down to the local big box store, and I purchased a non-contact voltage tester. I tested for voltage at the motor (I actually removed one of the plates so I could get within .25 inch), but there was no voltage. I then followed the wires back to the Aquastat. Inside I found two sets of black and white wires. One of the black wires registered as having voltage while the other did not. Thus, my guess is one set is from the thermostat upstairs and the other is the downstairs one, and it is not working. Is it safe to assume that if I remove the wires going into the thermostat, and connect them together, that should send the signal to turn the circulating pump on (it's an old old thermostat, which operates at 110v, so yes I'll be careful)?

  • Dave Carpentier
    Dave Carpentier Member Posts: 594
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    Post a pic of the aquastat with the cover off ?
    30+ yrs in telecom outside plant.
    Currently in building maintenance.
    mattmia2
  • Steve27
    Steve27 Member Posts: 12
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    Well after taking the thermostat apart, and getting nowhere, I started looking at the aquastat. After cleaning up a couple of the connections, It appears I'M UP AND RUNNING!

    Thanks to everyone for your info and insights, and a big thanks to Jamie Hall, that non-contact voltage tester really helped.
    PC7060