The recirculation filter unit ULBF must be replaced every 1.5 years (300 operating hours), recirculation unit UUE1 once a year and recirculation unit ULB3X every three years or every 600 operating hours. The integrated filter (PUAKF) on the BORA X Pure and BORA Pure cooktop extractor systems and on the BORA Basic (BAKFS) and BORA GP4 (BAKFS) should also be replaced on a yearly basis or every 150 operating hours. The integrated filter indicator notifies you when this period has passed. This link will take you to mybora shop, where you can easily order your replacement filter. You can find more information on changing the filter at https://www.bora.com/int/en/service/filter-replacement/