Turn off power to the water heater at the breaker
Remove the access panel covering the thermostat
Remove the insulation and plastic safety cover
Set a multimeter to the lowest ohms setting
Check for power at the thermostat terminals if needed
Test continuity across the thermostat terminals
Compare the reading to the manufacturer’s specifications
Test the upper thermostat first
Test the lower thermostat if the heater has two thermostats
Check the high-limit reset button for tripping
Press the reset button if it has tripped
Replace the thermostat if it shows no continuity when it should
Reinstall the safety cover, insulation, and access panel
Restore power and verify proper water heating