Error message 'Fill up water

Hello
,after a repair from private I get from my Nivona NICR 830 type 691 the error message 'Refill water', although the water tank is full. If I intentionally put the water tank slightly misaligned, she recognizes it. If the water tank is correctly seated, it does not recognize it. Of course, the first thing we do is guess at the sensor. But it sits firmly and is wired correctly. Does anyone have any ideas?
I thank you in advance for answers!

We have the same problem with the Nivona Type 573.
It has not been tampered with, but just randomly starts saying that there is no water in the tank even when the tank is full and correctly placed.
I can sometimes get the error to go away by taking the tank out and replace it a few times, but now the error persists and I cannot make it go away.

You need to change water tank sensor.