Open tap - filling system - close tap

Try using warm water in the watertank, important that the water is not too hot, it can cause leakage in the o-rings in the fluidsytem.
Repeat the procedure a few times, if nothing helps, turn off the machine and wait 1 hour and try again.

If you can`t get around this message, then the flowmeter needs to be changed.

Using hot water with descaler works even beter then just hot water. I had to repeat the filling process many times with hot water with descaler before the flowsensor started working again

We have the Impressa F60 and ran into the same problem. I finally called Jura support. The tech told me to remove the grounds tray, and to take a dry paper towel and reach way back inside and wipe out the grounds. On my model there is a plastic flap that you have to go past and wipe the top of the chamber. Anyway, I was HIGHLY skeptical that this would work, but it did! Now, every time I empty the grounds I wipe this out. If we forget, the open tap issue eventually comes back.