Inside the exterior access door there probably is a switch that needs to be turned on, providing it was turned off in the first place.
It may be an Atwood or Suburban, a 6 or 12 gallon heater. The element is easy to replace and many can be found on Amazon at a good price.
However, with the statement that says the water is warm for a second sounds as if the water heater winterization bypass valve is still open.
Retrace what you did when you winterized and reverse the order. An element won't go bad from sitting over the winter. It will burn out but a 2012 should still be good UNLESS you happen to have drained it while the electricity was still on. A dry element will die very quickly without water to keep it from running away with itself.
One of those two would be my guess, a dry tank or the bypass valve being open may be the problem.
It's anyone's guess what the manufacture had that day for heater installs.
2013 Voltage 3800, 2012 Chevy 3500 HD
2010 Yamaha V Star 950
2009 Yamaha Raider
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