The Caleffi XP polyphosphate dispenser, code 545950, is an effective solution to prevent limescale build-up in domestic hot water systems. Installed on the cold water supply pipe to the boiler, it proportionally releases polyphosphates that protect internal surfaces from scaling and corrosion. Fitted with 1/2" M x 1/2" F connections and supplied with a crystal refill, it ensures an average treatment time for 35-40 m³ of water, helping to maintain system efficiency over time.