Will flush but sometimes it won’t refill. How do I Check to see if water is coming into the valve?

Thank you for posting this review concerning your product issue. Here is a quick tip that may help; when the fill valve will not turn on, unless you tap it, this is an indication that debris may be trapped inside the valve. The number 1 solution in resolving this problem is to flush out the valve and rinse the master seal. This instructional video is for the 400 series fill valve new or old and should resolve the issue -https://www.fluidmaster.com/toilet-repair-videos/flushing debris. For additional help with your installation contact Fluidmaster’s Technical Service Department, we are available Monday through Friday from 5:30 AM through 5:00 PM Pacific Standard Time. Contact options include: Chat www.fluidmaster.com/support E-Mail techsupport@fluidmaster.com and Toll Free 800-631-2011.