To adjust the temperature on a gas or electric water heater, set the thermostat or adjustment screw's temperature dial to 120 degrees Fahrenheit. Alternatively, check the temperature of the water using a thermometer once every three hours, and adjust the thermostat or adjustment screw until the temperature is set as desired.
If numbers are marked on the temperature dial of gas or electric water heaters, adjust the temperature to 120 degrees Fahrenheit.
If the gas water heater does not have numbers marked on this dial, collect hot water from the tap closest to the unit in a glass, and check its temperature with a thermometer for three minutes.
If the thermometer reading is below 120 degrees Fahrenheit, increase the water heater's temperature. After three hours, check the temperature of water again in the same way. Repeat the process until the desired temperature is attained, and mark the location of this temperature setting on the thermostat.
In electric water heaters without a numbered temperature dial, switch off power supply to the heater at the circuit breaker. Locate the two adjustment screws of the two thermostats under metal covers and behind some insulation inside the unit.
Turn each adjustment screw clockwise to increase and counter-clockwise to decrease the water temperature. Restore the insulation and covers of the heater, switch on the power supply, and test the temperature of water manually as before.