Unplug the kettle and let it cool completely
Empty any water from the kettle
Fill the kettle with equal parts white vinegar and water
Bring the solution to a boil or let it sit for 30 to 60 minutes
Turn off the kettle and let the solution cool
Pour out the solution
Scrub any remaining scale with a soft sponge or brush
Rinse the kettle thoroughly with clean water
Boil fresh water once or twice and discard it
Repeat as needed for heavy buildup