Original post by: Steven Theakstone ,
I have a WF-3520 that stopped sensing paper in the ADF. Open the top cover of the ADF. Near the top edge of the ADF there are some holes in the base plate where a plastic tab (that is in the cover) fits. This has a sensor that can collect dust. Clear the sensor by blowing or using a cotton tip - you will hear a beep when it has been cleared.