The red reset button or ECO or energy cut off turns off power to electric water heater.
The ECO responds to temperatures in excess of 150 degrees F.
You can use thermometer to check water temperature immediately after ECO trips.
Compare water temperature against the thermostat setting.
There are 4 things that can cause ECO to trip:
1) Bad thermostat is sticking and letting element continue heating water, or ECO is reading incorrect temperature.
2) Factory installed insulation and cover missing from tank, and thermostat is exposed to cooler air and misreads tank temperature.
3) Element shorted to ground in center of element. This completes 120V circuit to ground which will cause element to continuously heat the water.
4) Loose wire near ECO causing high-heat electrical event.Solution:
Check for missing insulation.
Check screw terminals for signs of high heat and burning >> tighten screws.
Replace both thermostats using detailed instructions given on link below.http://waterheatertimer.org/How-to-replace-thermostat-on-electric-water-heater.html
If the problem continues after replacing thermostats, more troubleshooting is needed:http://waterheatertimer.org/How-to-troubleshoot-electric-problems-with-water-heater.html
For more self-help information about your electric water heater:http://waterheatertimer.org/Do-it-yourself-water-heater-timer.html
For more help, add a comment and I will respond