There is a temperature control device (called a disc, or clicks-on) that opens the control circuit when it senses that it (above setpoint) is hot, and closes when it cools down some (maybe 10 degrees below setpoint). Just like a thermostat on your furnace. Yours is not opening the circuit, causing your manual reset high-limit to trip out. I had one that was loose and not making good thermal contact with the tank that caused the same problem you're describing. I cleaned the contact area and re-installed - problem solved.
You might want to actuate your Temperature and Pressure relief valve for a few seconds to be sure the tank is full of water. Be careful, as hot water will spray out as you raise the lever.
If you can read a schematic, use a multi-meter, and not electrocute yourself there is no need for "the man." Schematics are on the water heater, in the manuals, or on the internet.
If not, I suggest calling "the man" and getting your credit card out.