Part #100108683, Water Heater Thermostat, Upper / 7.25 x 2.25 x 0.75. This thermostat (part number 100108683) is for water heaters. Thermostat 100108683 monitors the water temperature and turns the heating element on and off. Disconnect electrical power to the water heater or shut off the gas supply before installing t... - Part #100108683, Water Heater Thermostat, Upper / 7.25 x 2.25 x 0.75.