[rvitko]

I would start with the self diagnostic test of the optic sensor.

1) With the sensor completely wiped dry plug in the controller.
2) All 4 lights will flash and it will beep, a single light will show for 1 seconds and then the normal 15-20 second pump run at startup will begin.
3) This light that is on one second is the optic sensor status, green means pass, yellow means it is marginal, red means it failed.

Assuming it passes, the next test is to catch it in the act of an overfill, if you wipe your finger under the sensor and the fill stops within 5 seconds, the cause is bubbles. The sensor should be relocated to as calm and bubble free of a location as possible. Be sure that the top off hose is not near the optic sensor as bubbles are added by the splash of the fill.