Neff Dishwasher – Not enough water?

Hi,
our Neff S5543x1GB/17 isn’t cleaning our dishes very well.
I’ve checked the pumps and the pipe work for blockages. Whilst a couple of the drain pipe had a coating of silt, I don’t think that the flow was significantly reduced.
Previously, if the door was opened during opperation, the water level was visible above the mesh filter in the floor of the machine, and significant water flow was evident from the spary arms, but now, when the door is opened, the water flow is poor, and te level is below the mesh filter.
I’m thinking that there is just not enough water in the machine.

Is this likely, and if so, why?

Thanks in anticipation!