Got a used Cal spa 2100 electronic series. Hooked up correctly and ran fine, but discovered leak around one of the pipes. Drained tub and replaced bad gasket. Refilled tub and turned on tub. Ran for about 10 seconds and then GFCI breaker kicked off. Everytiime I try to turn it back on it trips right away. I was hearing a click sound from the control panel inside of tub, so I took off cover and seen that there seems to be a small contactor that was closing as soon as breaker was turned on. I am not sure where to go from here. Everytime time I turn on the breaker, I hear that contactor snapping together and immediately the breaker kicks off. I can't even get the tub to stay on long enough for it to do a self diagnostic check. Any suggestions as to what to do next would be most appreciative. This is a brand new spa gfci breaker box, so I am almost 100 % sure that it is not the breaker.

Try unplugging components one at a time. Heater may be hard wired, and may need to have BOTH heater leads disconnected to isolate.

Since it ran for 10 seconds before it tripped, it's probably wired correctly. It's likely tripping because a component is leaking electricity, or something got wet. Try disconecting the heater, air blower, ozone generator (if equiped), etc, etc, one at a time, and see if it stops tripping.

Good luck!