There are several posts on the web reporting ground faults on this pump. With the pump I repaired the fault was produced by the enclosed heater in the impeller housing. Turning the pump upside down allows removal of the rubber feet to access the four screws to be removed exposing the circuit board and connections to the heater. The wiring from the heater is yellow and orange and attach to the board with Faston terminals. Remove those and check the resistance to safety ground. In my case measuring with a Fluke 87V the resistance started over 100k and would fall to about 30k over a few seconds. That was enough leakage to through the GFCI. The fix for this job was to disconnect the heater and the fault went away. I understand the heater is obsolete. In order to get at the heater, although I recommend just leaving it in, the pump housing and impeller need to be removed. The impeller is threded with a right hand thread. The armature can be held on the opposite in with a flat head screwdriver in the provided slot. The performance of the pump after the repair when installed in an 80 gallon whirlpool tub was a loss of about 7 degrees F of water starting at 110 degrees F after about 15 minutes.