Ok, this one is driving me crazy. I have a marquis sports series 500 spa. 6 years old.
We have had NO problems till now. I popped the breaker (*hit the test button), drained it, filled it, went to click it back on, and it won't. Click the breaker and it immediately trips and the breaker flips back off. I had my electrician check the breaker and he said its fine.

So, the question is, how do I figure out what's gone bad in the hot tub? My guess is it's the heater, but really.. its odd how something broke between empty/fill.