Simply half fill the kettle with COLD water and pour HALF the sachet in. Switch on the kettle & boil the water so the process can begin. Wait for the water to completely stop bubbling carefully check to see if all scale has gone, if not boil again. Rinse kettle with fresh water & then boil again. Rinse again with fresh water. warnings Steam burns, keep clear Water may boil over if you overfill Make sure you rinse throughly Keep out of reach of children.