For the good long term performance of humidity measuring devices it is of highest importance that the sensing head is kept clean. In most of the applications the choice of appropriate filter cap is enough for achieving this.
In polluted applications the filter cap might get clogged. Long response time of the device indicates a dirty filter cap, which shall be replaced by an E+E original new one. Please see the choice of E+E filter caps in the “Accessories” data sheet at http://www.epluse.com/fileadmin/data/product/accessories/datasheet_accessories.pdf and contact your E+E sales representative for advice.