Also possible that a terminal in a "quick box" like Trailers and RV's use, has given out from the prolonged high current draw that a water heater represents. With power off, check for continuity of Switch, Thermostat(s) and Element. Disconnect each for testing so you don't see continuity from something else. Then re-connect and power it ON. Do you have 120 VAC at Switch, Thermostat(s) and ONE side of the Element? Other side of the Element is Neutral, should be wired White, and NOT have 120 VAC. If it does, then what happened to me has happened to you. Failed Neutral connection. We have a junction box adjacent to the water heater and that's where the failure was. Easy to fix, but I'd spent a day focusing on elements, switches, thermostats... If you don't have 120 VAC at Switch, Thermostat(s) and (one side of) Element, you could have an open HOT in a splice box. Ours just happened to be Open Neutral.
