Pump(s) appear to be tripping breaker

I have a very old Tiger River Spa. It has a Watkins Jet pump and Watkins No-Fault heater. It has been running with no issues for years. The other night we went to use it and water was lukewarm. I realized the breaker had tripped. When I tried resetting the breaker it keeps tripping. Doing a search online yielded the most plausible theory was a bad heating element. So I disconnected the hot from the heating element and still trips breaker. Then I reconnected the heating element and disconnected the Water circulating pump and breaker stays on. Then confusion set in because I plugged that back in and disconnect my Jet pump and breaker also stays on. Is it possible BOTH are bad at once or does one rely on the other or something? How can I isolate which part I need to replace?
 
I disconnected the hot from the heating elemen
Both wires are "hot" as far as a gfci is concerned.

disconnected the Water circulating pump and breaker stays on.
The heater cannot run without the circ pump.

Not saying it's not a pump, just that it's harder to pinpoint than that.
Also, breakers go bad too, often along with another failure (heater, pump) which could be the case here. The fact that you have multiple culprits tripping it suggests so.
I'd do individual ground fault tests on each piece of equipment independently. This is done with a good quality ohm meter.