Are you sure it is primed properly. If it is sucking in water & the cannister & hoses are full, then just the effect of the cannister being continually re-filled from the sucked in water should push water up & out the hose. So if it's not doing that, I suspect it's not primed properly. I find my 2028, sometimes the self priming thing doesn't work as well as it should, so I have had to resort to sucking on the outlet tube.
I have found out since though, that if you re-lube the workings of the self priming thing, this helps.
For a filter to be primed, the cannister must be full of water and both hoses should also be full. Is this the case with yours?