Grundfos pump motor hums


After 30 years use, I replaced my water heater pump Grundfos model UP 15-18 with a new unit 3 years ago. I just noticed it no longer seems to be working: it just hums very quietly, no vibration whatsoever. The capacitor measures 10 uf as rated. I have 46 ohms resistance between the plug, zero to ground. Before I replace [fairly pricey], any other tests or ideas? Thank you.
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wrote:

Do you mean a circulating pump for hot water heating?????
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Thee is a screw on the back of the motor. Remove it and inside you can see the shaft. With a small screwdriver, you can turn the shaft a bit. This can be done with power on or off. If the power is on, it may start to turn slightly and then pick up speed. When mine were getting old, I had to do that at the start for heating season, they they were good for the year.
When one of the pumps finally did go I replaced it with a Taco. It was just not as quiet, but it did pump water just fine at half the price.
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This pumps water through solar panels. I tried turning the shaft. Frozen solid [after only 3 years]. Guess the bearing is gone. Not impressed with the price/quality. I'll look into a Taco. Thank you.

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I wish as these cost @ $200. You'd think there might even be kits available. But I tried replacing the bearing with the last one and I'd say Grundfos really didn't make these bearings "user serviceable."
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As to your original post, check the amp draw. That's totally valuable information.
Hope you can dissemble the pump, clean it up, and make it last for a few more years. Some electric water pumps (Bell and Gossett comes to mind) have oil holes to drip in some ND20 oil.
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Christopher A. Young
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wrote:

Sounds right , modern quality, old unit works 30 years, new unit works 3 years. I have old boiler pumps that never failed and a new recirculator lasted about 3,
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Cause it doesn't know the words.
We now return to your regularly scheduled posts.
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I've search but not found Grundfos parts and assumed I'd have to buy a new pump. I was pleasantly surprised that the local Grundfos dealer encouraged me to bring the pump in for a free disassembly. Pump had overheated [showing brown build up in interanls] but bearing was good. Dealer installed a new rotor/impeller assembly and unit seems good as new. $25. I was shocked by the high level of service.

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Always nice to hear a happy ending. Any idea what caused the buildup? Was it gunk in the system?
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No idea. The water here in Hawaii is soft - rain water filtered through lava dikes. My pipes are 30 year old copper but I never see crud in any of the faucets. The brown residue was very thin, just enough to upset the tolerances of the low hp motor.

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Inexpensive, good quality service? That's rather rare, and good to find.
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