Primimg a Ehiem

I have a Ehiem that seems to have gone ka-poots. Anyone have any Idea
on what I may check for before I dispose of it?

When the canister is full of water and I turn it on it just wont pump
and flow. I took off the head and checked the impeller it seem to be
working. The media within the canister isnt over loaded because it
will work under a sphion type flow. Is there somthing I maybe missing?
Any suggestions or maybe a common replacement part that need to be
changed.

The Ehiem is an 2015 (old one) worked well before I put into storage
some 10 years ago. I already purchased a new one for my tank (2215)
but thought I would maybe fix this one and keep around for use on a
sick tank in the future.