I see there is a recent thread with a similar issue. I've had this unit for 3-4 years most likely. It hasn't been touched in close to 2 and that does include no cleaning. I soaked the entire magnet with optical sensor and float switch in vinegar and some calcium build up came off but nothing drastic. Occasionally I have minor issues like overfilling but now the unit doesn't work at all. I believe the optical senor is the issue since if I flip the float switch it will just beep too high like it's supposed to. Here is a breakdown of what happens : I turn the unit on and it will start up normal : green light for level on, approximately 1-2 seconds later the yellow light will come on for too low (for the purposes of this test the sensor is completely out of the water). The pump will come on for just a couple of seconds, water comes out like normal but then all lights will flash red, orange, green, red and beep for approximately 1/2 a second. The entire cycle will repeat with some variation. Sometimes the level won't come back it will just go to too low, start the pump for one second, all 4 lights come on beep repeat. The pump is only on when the too low yellow light is on. I think that is a pretty clear explanation but if need be I will take a video and post it. I notice the optical sensor is one part that is not sold as a replacement part. I have also red previous threads where its mentioned this rarely fails. I know the pump still works and the float switch also does appear to work. I am open to suggestions as to what to try next. Again this unit basically hasn't been touched in close to 2 years and was also in service for close to 2 years prior to this. No new equipment under the tank or anything. It's not pretty but the wires are not tangled up nor should there be anything new causing interference.