DIAGNOSIS That's a 'Power Failure' code. It means the unit lost power while it was running and is now in a protective restart mode.
FIX It's designed to be simple. 1) First, press the Power button on the unit itself to turn it off. 2) Unplug the dehumidifier from the wall outlet for a full 60 seconds. 3) Plug it back in firmly. 4) Press the Power button again. The 'PF' code should clear and it should start up normally. You'll need to set your desired humidity level again, as the memory resets.
IF THAT DIDN'T WORK If the 'PF' code comes right back after you plug it in (before you even press Power), the issue might be with your wall outlet or power cord. Try plugging it into a different outlet that you know is working. Check the cord for any visible damage.
HEADS UP This is a common 'feature' on these units after a brief power flicker. If your home has unstable power, you might see this often. Using a surge protector can help, but don't use an extension cord.