I've found that when I unplug my Tunze osmolator it starts up and then will start pumping water, even if the optical sensor is submerged. If I lift the float switch it will beep and turn off but then return to on once I let go of the float. I've been able to fix it by taking the optical sensor out of the water and then putting it back in the water will make it return to normal function. What could be happening?