Wy is my machine not working?

Hi - I'm getting the H20 error code on my WMF720 Aquarius +. If I switch off then on, it tries to start a few times then nothing. When switched off and on, the machine will recognise a different cycle if selected but produces the same result.

I have blown down the pipe to the pressure switch and I'm happy there are no blockages here. Similarly, I have checked the filter on the bottom right at the front, this too is clear. I'm happy also that he pipe to the drain is clear.

What could it be...?