Perhaps the magnet is reversed on the float sensor? It looks like mine and you can remove the c-clip holding the float(magnet) in place and then reverse the float and replace the clip. Doing this changes the polarity of the switch so that once was a high sensor is now low or vice-versa. Try it the other way to see if that is the issue. Maybe make a mark on the float with a sharpie first so you can go back to the way it was originally.
