Karcher pressure washer K6.50

[Bushbaby]

Hi all,
I finally had an opportunity to look at the washer today. The mesh filter was full of crud but it's still not working. The pump is working and I have noticed when I first switch on there appears to be rusty coloured water that is pumped out and then clears. There is still no pressure. I fear that it may well be the pump unit.
Oh dear!

Regards

Rob