If your Fleck 5600 Valve is not refilling the water to your brine tank,
then here is a list of things to check and information to review about Brine REFILL Failure.
see:
Brine Line Flow Control button clogged?

and
Brine Cam Gear Setting is what Opens the Brine Valve Piston for Refill to occur.

Watch the videos below the parts description.
Salt Setting Adjustment on Brine Cam Gear
and
Check Injector Set for Clogging of the Injector Set or Screen

And if you disconnect the Brine Tubing at the Valve and you have water flowing out during Brine Refill as it should, but not when connect to the salt tank,
then the problem is the Brine Pick Up Float Shut off and it should be replaced,
Brine Pick Up with Float Shut

For an instructional Video about manually advancing the front control knob through the Cycles of Regeneration,
See the video listed below this product ( 12 day power head ) for a better understanding of operation,
Fleck 5600 12 Day Cycles and Setting