Furex Kettle Cleaner 12 x 250 mlKettle de scaler. A clean kettle boils more efficiently! Fast action. Furex contains Formic Acid 40% with Additives. 1. Half fill kettle metal or plastic with water and bring to the boil. 2. Unplug and stand the kettle in an empty sink. 3. Add approximately 80ml of Furex descaler one third of the bottle and leave for five minutes or until the effervescence stops. 4. Pour the contents away, rinse thoroughly and wipe clean. 5. Refill with fresh water,