The F code means your unit needs to be FILLED with water.
If your unit is full with water and the F code still engages, this means the float rod is not positioned correctly. To install the float rod, turn the cabinet upright and place the wide end of the float in the circular area in the bottom of the cabinet. Make sure the float retainer is between the first and second bumps on the float. Squeeze the float retainer’s prongs together, position them halfway down the long vent slat, then release the prongs to lock in place.