Fixing the coolant level false warning issue (Opel/Vauxhall Zafira B)

*Please read the update on the end of this text. Annoying false warning was thrown at me every couple minutes while driving the car. Not enjoyable. After about a year and after many failed solutions I have finally (I hope) found solution for this problem. Now I feel like expert in this area :-) * Although sensor was lose and contact bad the real problem was bad tank. After tank was replaced it works fine (more then month now). So the floater in the tank was stuck after all. Cleaning the tank did not help in this case.