Originally Posted by dhays
If it was me, and since I don't know anything, if the breaker has other 15 amp breakers next to it, I would just hook up the water heater to another 15 amp breaker and sea what happens. If it trips then the water heater or the installation is the problem. If not, then you could replace the breaker.
But again, that is only what I would do, not what somebody should do.
I did this with a spare 15 amp breaker with jumper wire. After 30 min no tripping of breaker. Tried the first breaker again and it last a minute before tripping. Going to replace with new breaker and that should take care of the problem.