Turn the heater on with the power button. Close the gas supply valve and the hot and cold water valves. Close the drain valve lever handles. Depending on the model you have, these valves are likely on the bottom of the unit.
Take off the drain caps, located just underneath the drain valve lever handle. Attach a drain hose to the drain valve outlet of the hot water valve. Attach the pump outlet hose to the valve outlet for the cold water. Place the other ends of the hoses into a 6-gallon bucket.
Add 5 gallons of white vinegar to the bucket.
Turn both of the drain valve lever handles until they are fully open.
Turn on the pump and wait for the number “11” to appear on the display of the remote controller. Wait 45 minutes for the vinegar to circulate within the unit.
Turn off the pump. Close the cold water drain valve, remove the hose from that valve and place the cold water drain cap back on.
Empty the bucket of vinegar. Place the hose connected to the hot water valve back in the bucket. Open the main valve wing handle for the cold water. This valve is located opposite the cold water drain cap. Wait a minimum of five minutes for the cold water to flush the heater.
Turn off the cold water drain valve and remove the water inlet filter. Use a brush to clean the filter under running water before placing it back in the heater.
Turn off the hot water valve, take off the drain hose and put the hot water drain cap back on.
Turn the main valve handles for the hot and cold water until they are fully open. Check that the lever handles are closed.
Turn the gas supply valve until it is open. Press the power button of the heater twice to reset the unit.