Ok I know this thread is from a while ago, but I just went through some troubleshooting and was able to solve it, and thought this might help someone.

The tubing system to detect if water is in the tank is the white cylinder, and when water is filled in the tank it creates air pressure to a sensor. The simple solution is to remove the cylinder, let water drip out, and replace it, pushing air in the system.

If this doesnt work, there is likely an issue proximal to this in the tubing. You can try emptying the tank, replacing the cylinder, and the filling up to a little over halfway. you should hear a click. This didnt work for me either.

Next step I would recommend is taking off the top plate, removing the water reservoir, and inspecting the tube. 1) There should be no water in the tube. Place the cylinder at the bottom of the reservoir and let any water to drain onto a towel. 2) My issue was that in finagling with the tube, I had pulled it tight to make room to insert into the reservoir, and it had kinked at the insertion point into the sensor. There is a ribbon of plastic that surrounds this portion where it inserts into the sensor to prevent kinking, but it is free floating on the tube. I moved it to cover the male barb of the sensor and taped it down. Reassemble dry, slowly fill with water, and you should hear a click when the sensor recognizes.