The catalyst filter may be replaced if it begins to collect odor. When it starts to collect odor, you can first take out the filter and put it under the direct sunlight to dry out the moisture. The evaporation process can help to remove the odor. If drying doesn't help to get rid of the odor, it's time to replace the filter. You can order it through our website. Make sure to select the collect model (X3, X5 or X8).