Diplomat 8352 not filling properly?

My dishwasher has started to play up:
It starts OK with a drain sequence then maybe half a litre of water goes in which I can see when I open it.
Then it emits a constant humming sound and doesn't go into the full filling mode as it would normally.
It eventually pops the soap tray open and starts to fill up with steam but no more water goes in.
When I open it ALL the lights flash as the programme has been interrupted (not just 3), and there's no pool of water underneath to indicate a problem with the flooding indicator.
Why does it start to fill then not carry on to the correct level?
Any ideas anyone?