My degree is in Electronics and I have very little experience with hot tub repair. That said, can you run the tub for a couple of hours with the side panel off that gives you access to the electronics? My thought is that if its overheating and shutting (the electronics, not the water) then it running ok for a few hours maybe a sign that this is the case. If you can say that this is the case you might be able to further narrowing it down by hitting certain areas of the electronics with a hair dryer to see what shuts it down. FWIW