Fill the kettle halfway with water
Add the juice of 1 to 2 lemons, or several lemon slices
Boil the mixture
Turn off the kettle and let it sit for 15 to 30 minutes
Pour out the solution
Scrub any remaining limescale with a soft sponge or cloth
Rinse the kettle thoroughly with clean water
Boil fresh water once and discard it to remove any lemon residue
Repeat if needed for heavy buildup