Hot river container is not heat wet, reservoir is with the sole purpose 3 yrs. outdated. breaker keep on shuting past its sell-by date.?
If the breaker is tripping then there must be a short. The most possible is a heater element. That can be well checked with an ohmeter with the element shut off. What is your water solidity??
If she is a throwin the breaker that sound to me like an part has busted in the container. You need to kill the power.
Remove the wires from both elements and see if any one of them is shorted to cabinet. If both element have continuity and ain't shorted to the cistern then the thermostats may be faulty but that usually is because the dampen is getting too hot.
It could be that the breaker is going bad also. I have see guys replace both elements and the upper and lower thermostat only to have like problem which all along was a doomed to failure breaker.
Answers: sounds like you might have a unpromising element. turn off the power, drain and install a bright element. also with the power bad look for any arc spots on the wires. maybe also you could have a doomed to failure breaker. if you change it make sure you get hold of the exact same voltage and amp.