Have you replaced or tested the relay that is right near the heating element, that is what turns it on and off? According to the wiring Diagram I have for our water heater the white (neutral) wire goes directly to one side of the heating element, the hot wire (black) goes to the relay and a short jumper goes from the relay to the other terminal on the element.There is a yellow wire that comes from the control board that activates the relay when the 12volt switch on the control panel is activated. I would check to see if the relay is receiving power on the yellow wire when you have the 12volt switch on. If the relay is good you should have 120volts at the element. Good luck.
In our mh the breaker is the only way to turn off the 120 power.
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