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Grundfos 15-58 Help

I have a Grundfos UPS 15-58 FC running a secondary loop radiant system for a 2nd floor that is rarely used.  I went to fire it up and nothing but a slight hum.  I removed it, replaced the capacitor, and reassembled it but the wire broke inside the black housing pictured. I repaired the wire but the disk that looks for the world like a hearing aid battery that normally resides here took a fall and went missing.  I disassembled the pump, wired it up to 110v, and with a little push on the rotor it spun right up.  Without it, just the familiar hum so I do believe a bad capacitor was the initial issue but now I am without said disk.  Can anyone tell me what it disk does, how critical it may be, and if someone might  be interested in selling one you might have. Thank you.


  • hot_rod
    hot_rod Member Posts: 22,491
    I think it causes a tickle effect for to motor. Intended to prevent them from sticking after long periods of non use :D
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Alan (California Radiant) Forbes
  • HomerJSmith
    HomerJSmith Member Posts: 2,511
    That pill that you lost is a capacitor that probably levels out the DC that the diode rectifies. Capacitors store DC not AC voltage. If someone has an old pump pulled out of service that they are going to throw away that has that Grundfos connection on the capacitor, they might open that black thingy as you did and send you that brown pill.