Turn off the power or gas supply to the unit
Shut off the cold water inlet and hot water outlet valves
Open a hot water faucet to relieve pressure
Remove the service port caps on the isolation valves
Attach hoses to the service ports
Place the hose ends into a bucket or drain
Close the hot and cold isolation valves
Pour white vinegar or approved descaling solution into a pump or bucket
Circulate the solution through the heater for 45 to 60 minutes
Turn off the pump and let the solution sit if needed
Drain the cleaning solution from the system
Flush the unit with clean water until clear
Clean or rinse the inlet water filter
Reinstall the service port caps
Open the cold and hot isolation valves
Restore power or gas supply
Run hot water at a faucet to purge air
Check for leaks and normal operation
Repeat descaling every 6 to 12 months or as recommended by the manufacturer