Why does the High Temp Shutoff keep tripping? The water heater has been installed for four years and no adjustments have been made to the temp settings. However, for the last week it has been tripping the High Temp Shutoff switch.

Assuming the water heater really is at the high temperature limit, then the thermostat is fusing it's contacts occaisionally and needs to be replaced. This is what the high temp cutoff is supposed to detect.

Either the switch or thermostat is bad. If the water is abnormally hot when the switch kicks off, the thermostat is bad. May take some work to catch it before the water cools off.

Hot water heater high temp button continues to trip. Changed both heating elements, both thermostats (upper one twice) continues to trip. Verified 120 volts on both incoming red and black wires and properly grounded.