Power steering help please

Hi all
I have a problem with my power steering on my 300tdi where it is very tight and notchy when I try and turn the steering without moving? But as soon as I start moving its fine at any speed!
I cannot see any leaks and the fluid is topped up, so could it just be a worn pump or can anybody advise some help with this?
Thanks for any help

Maybe one of the ball joints has had it, that's first place I would look

ujs on stering linkage are often the cause of notchy steering but since yours is fine when driving it could easy be low pump pressure does it improve when engine revs raised ,or poor box