Hotpoint df61 dishwasher not draining - water circulating?

Dishwasher is not draining.
Have checked filters, spray arms, opened outlet under filter to check thingy spinning and not blocked. Not sure how freely it should spin but it does when I flick it round.

Opened up side of dishwasher - water appears to stop flowing before contraption with red valve in it, removed this cleaned it. Problem remains.

Emptied water from entire machine. Now running it. Problem seems to be linked with red syringe/spring - if I pull it down water starts moving around system.
Any ideas - thankyou