Sump pump continuously running, however the float doesn't appear to be stuck.?

My sump pump is running continuously, however when I checked the pit it doesn't appear anything is impeding the float. I unplug and replug in the unit and it sucks down the water, but then it just keeps on running. I just replaced this unit last summer. Any ideas? My guess is the switch has gone bad, that's the only thing it could be. Since the switch is integral to the pump (Simer 3984), I'll need to replace it.