Under no circumstances should anything other than citric acid or vinegar be used, as other substances may cause irreparable damage. You can either: 1. Mix one sachet of citric acid (0.35 oz/10 g) with 7 oz/200 ml of water. Ensure basket is in place and pour solution into warmer. Heat for 10 minutes on setting 3. After 10 minutes, switch off by unplugging from the wall and leave to stand for 30 minutes. Pour the solution away and rinse the warmer with water from the faucet. Citric acid is available from most pharmacies and through Philips AVENT Customer Service. OR 2. Pour 2 oz/50 ml of vinegar (white) mixed with 4 oz/100 ml of cold water into the warmer ensuring the basket is in place. Allow to stand in the unit until any lime scale has dissolved. Empty the unit and rinse thoroughly.