Turn off the water heater power or set it to standby
Shut off the cold water supply to the unit
Close the hot water isolation valve
Connect hoses to the service valves
Place the other ends of the hoses into a bucket or drain
Open the service valves
Pour white vinegar or descaling solution into the bucket
Turn on the circulation pump and let it run for 45 to 60 minutes
Turn off the pump
Close the service valves
Remove the hoses
Open the cold water supply valve
Open a hot water tap to flush out the unit
Let water run until it is clear
Close the hot water tap
Restore power or set the heater back to normal operation
Check for leaks and confirm proper operation