I'm at a campground, which we normally don't do, and went to turn on the electric element for the water heater, but it's stuck in the off position. (From lack of use, since we usually boondock.) Is ...
You are at the first stage of the switch failing. The little spring loaded button is melting. Soon it will switch but not make electrical contact. Take it off and go to Ace Hardware. They have ones that pop in the same rectangular hole. AND you can mount it so top in is on, as it is not labeled like the upside down OEM switch!!!!!
Just ask me how many times we did not have hot water last year to figure this out!