Product review (5 stars): Raise your drain pipe.  Maybe
Well, like everyone else I've been have repeated problems with this part for a while. I did the blowing in the hose and tapping and it worked for a while. Now nothing worked so I bought a new one. Read an article that said repeated failures could be caused by the drain pipe being too low. It should be 42 inches from the ground. If it's lower it could cause sifoning of water back into the sensor which causes the contacts in the sensor to fail. Hopefully this helps. New sensor works perfectly so far.