Simpson Encore Washing Machine not pumping water?

My simpson is not pumping water so is unable to spin by itself. If I gravity feed the water off by placing hose at floor level it drains off and will then spin. The pump is making a humming noise.

The machine is a Simpson Encore 605 and it's about 3 years old and has had light use only.

I put a few pairs of dirty tramping boots in and there was quite a lot of muck on them (including some bark) which overfilled the lint container.

Any thoughts?