Most lower thermostats do not have a reset button. The red button is called the emergency cutout (ECO). Thermostats only cut one leg of power to the elements. A stuck thermostat or a broken element leaking to ground results in a run away WH. The ECO trips on high temperature and opens both legs of power. Placing the ECO on the top thermostat protects the whole WH; regardless of what fails electrically the ECO kills the power.