Grundfos Pump Teardown - What Caused It To Fail 

The first pump was destroyed by sucking up parts of the heating system. There was no gravel or dirt getting sucked into the system; pipes do not work that way. When there is pressure on the inside nothing can get in. The 'dirt' and debris is normal to see in older systems, sloppy builds, and any system with anything that is made of iron. We always install a strainer on the input to any boiler or heat pump system. The first pump could have got jammed and lost flow through the motor and it over heated. There was nothing wrong with the second pump and it looked fairly new. The rotor shaft end play is perfectly normal. The stator shaft is surrounded with water when in a system. This is why you have to 'burp' out the air after you put in a new pump. The water cushion cools the motor and acts like bearings made of water. The end play actually reduces wear and acts as the side of the bearing to keep the motor from rubbing against the case.

My dad found the chinese version of those pumps for $12 so we bough many just because we couldn't Believe how cheap they were, it actually blows my mind how they can do it so cheap, the bearings are actually ceramic bushings! Only issue we have found so far is, the power cord stinks, and the pump cover were the water inlet goes into the impeller is not well made so there is water recirculation within the pump making it lose some pressure but still not bad for $12, full metal construction and all.

I had one that wasn't pumping but on investigation the rotor was free spinning and the windings were fine. It turned out to be the motor run capacitor. Interestingly, Grundfos print the value of this on the label (usually 2or 2.5uF). They are easy to source and fit. You just need to make sure it fits in the space available in the connector housing and is of the right voltage rating (usually 450vac)

“What is that ?” Lol maybe gold😮😊

What size hex did you use?

the little plastic item you removed from the first pump should NOT be in the pump. It is a vacuum break that comes with the air vents, and should be installed with them. But it somehow got disengaged from the vent (or were improperly installed) and ended up in the pump. Not many hydronic experts in my area so I am having to become one! I have replaced my pump before but today I will remove it and open it up to see if I can fix it.

If I did that on my wife's kitchen counter top she would kill me..

I'm amazed that you got away with doing that tear down on the kitchen counter top. But instresting to see the disassembly. How old was each pump?

So where can you get a cartridge

chancer