My main 2 speed pump overheats on low speed with load applied. If you shut off the water so the pump just runs, it does fine. But once it is pumping water it sounds as if it is overloaded. It slows down to the point that it tries to restart, all the time getting hotter. Finally the internal thermal proctector trips and lets the motor rest until it cools down, then it starts the cycle again. I have rebuilt the wet end and replaced the bearings in the motor itself. It runs fine on the bench, but not when pumping water. Any ideas? Thanks. -Tim

It's possible that your control system is not turning off the low speed when it tried to engage the high speed, this causes the motor to be of two minds about what speed it should be running and causes some "interesting" noises and then the thermal protector cuts off. Try disconnecting the wire (either black or red) that controls the low speed and just run it on high to see if it runs like it should.

Double check your wiring to the motor. Is it running OK on "high speed"? Get an AMP meter and check amp draw to see if it is within perimeters on high. When testing on the bench, if it was totally assembled with the wetend did the shaft of the motor turn freely?