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45Doll

Grundfos Water Loop Pump Question

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If anyone on the forum has experience.

I just replaced a 28-year-old Grundfos UP26-99F 230V A/C water cooled pump that runs the ground loop in one of our geothermal systems and it's running fine now. I'll skip the whole troubleshooting experience and just ask my question.

The broken pump symptom was that the motor case got really hot, and the impeller wasn't turning. I pulled the external motor 'casing' off to reveal the internal 'cartridge' and its shaft that drives the impeller, and it wasn't mechanically jammed. That pump has a startup capacitor. If the startup capacitor was bad, would that cause the motor to overheat and not turn?

I don't have that much A/C motor experience. I previously replaced the startup capacitor for one of the compressors in our (previously replaced) geothermal heat pumps, but the only symptom there was the compressor simply wouldn't start. So, my thought was if the startup capacitor failed, this motor simply wouldn't turn. The fact that it got very hot very quickly made me conclude something in the motor internals had failed.

I shall attend any voice of experience that chimes in.

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11 minutes ago, 45Doll said:

That pump has a startup capacitor. If the startup capacitor was bad, would that cause the motor to overheat and not turn?

Yes, you could hear the motor hum, but not start.

Second thing I would check is bearings. Does the shaft turn easily? If it's binding, that could also cause it to overheat. A 28 year old pump, my first guess would be bearings.

Third, could be a dead spot in the windings. If the motor spins easy and fine, maybe it stopped at a dead spot. Spinning the impeller and trying to restart it would diagnosis it.

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Thanks @Sniper and @Scorpio64.

Bearings seemed OK, and the startup cap looked mechanically sound. It's about a 2" sealed type, not a wet electrolytic.

My curiosity is simply aimed at determining if I should have tried to replace the startup cap first (which would have been easy) before installing a new pump. Any other reason for the pump to fail would be (in my book after 28 years) cause to replace it. $335 for the new version that's three speeds, not fixed like the old one.

Curiously, so far, I seem to be getting about two degrees more heat out of the heat pump with the new Grundfos. I won't be sure about that for a while, but I'm going to monitor it. Since the new pump has three speeds I'll have to experiment to see if there's any significant difference in efficiency.

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13 minutes ago, 45Doll said:

Any other reason for the pump to fail would be (in my book after 28 years) cause to replace it. $335 for the new version that's three speeds, not fixed like the old one.

and that would of been my fourth suggestion. At 28 years, it's surprising it's still spinning. Replacing it would have been number one for me... being without heat isn't fun.

If the impeller spun OK, my guess would be dead spot on the windings.

13 minutes ago, 45Doll said:

My curiosity is simply aimed at determining if I should have tried to replace the startup cap first (which would have been easy) before installing a new pump.

Well, if the ratings on the old cap and the new cap on the new pump are close, you could do a quick swap of them and test the old one, to see if it starts the new motor.

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12 minutes ago, Sniper said:

At 28 years, it's surprising it's still spinning.

Not really. I have two other original models on our 2nd large geo HP that are still running fine. And back in the 80's I installed a couple Grundfos on a new boiler I put in our Randolph house. That's still going. They're a lot like Gould inground well pumps. Running for 30 years is not uncommon at all. But of course, nothing lasts forever.

The other thing I like about the Grundfos is that they use the water for internal lubrication. They don't depend on oil, grease etc.

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