Fisher & Paykel Nautilus DW691ED not washing?

Dishwasher has been working perfectly until now (it's about 5 years old). All of a sudden it is leaving the powder behind and not doing the wash part of the cycle.

It is as though it is going through that part of the cycle but not actually doing it... counter shows that it is counting down but doesn't seem to make any "washing" sounds at this time.

Still seems to do the rinse and other parts of the cycle OK, but dishes come out dirty and powder left behind.

Same problem on different types of wash (eg long wash and short wash) - never seems to do the actual washing.

Any ideas?