Icecap ato wont stop filling

My ato will not stop filling until it hits the white sensor. Even when the black lower sensor is submerged. I have 2 of these, I swapped the main controller and it did the same thing. Fills till it hits the white high level sensor, then stops and beeps. I think the low level sensor is bad. As mentioned I ha e tried another controller, cleaned the sensors, reset, unplugged and checked everything.