Do you have a multimeter? well it is good to check those, there are tons instruction, which i think is very helpful to troubleshoot the water heater.
btw check that there are no water leaks and inspect the electrical cables.
my home is using rheem, and depending on the usage, the replacement i had done, is due to corrosion inside the heater which i need to replace the whole tank, so i guess the current one is about 7 years plus.
I was informed by my dad that the circuit breaker trips when turning on the switch of the heater, following the troubleshooting video on youtube, isolating, removing all power cables, eliminated the possible cause of issues one by one, until i notice there is actually a short on the power cable itself. open up the cable duct and to my horror, it melts. The contractor has used a wrong type of cable, which cannot handle high current, AWG ... replaced on a better and correct for the appliance and it works.