This limescale filter adds a small amount of polyphosphate to the water. Polyphosphate prevents limescale from adhering to the boiler, preventing scale buildup and corrosion. This filter also contains an activated carbon filter, which improves the water's odor and taste. The filter has a capacity of 7,000 liters. The filter should be replaced at least once a year. In areas where the water hardness is above 10°C (10°F), a filter is recommended. A filter is not required for titanium boilers.