We occasionally remove the circular screen and wash it in detergent... accessed from under the fan. The screen, especially in the fan over the kitchen, will get some oil from cooking smoke and steam stuck on it. The screen will then catch and hold some dust. Also, the seal under the cap needs to be cleaned periodically because it too will catch some oil and dust, and cause the cap to stick down... such that the motor is unable to lift it off the seal. The seal must be accessed from the roof. While up there, I also clean the rain detector to make it operate better.