Need water heater make and model.
But, just guessing…..does it work on just propane? If yes ok good.
Plug in or generator, trips breaker, good, breaker doing its job.
1. The electrical side element shorted…..
2. Need to check ohms on electrical side unit.
3. Loose wire on electrical side.
4. Burned out electrical side unit, replace with new
All good, yeah.
Rvworks on youtube might help you understand better than me blabbing around.
Hope this helps,
Terry and Geri
2017 Four Winds 35SD
2020 Grand Cherokee Toad