I have a Fluval 305 and have had no problems.
Have you cleaned the impeller and impeller recess. Did you put both rubber caps on the ceramic spindle. Did they all align when putting it back together. I always run my top lid whist off the main body for a few seconds to check that the impeller is rotating easily. This is a little noisy but you can clearly see if the impeller is fee to move. Don't run it dry for more than a couple of seconds.
When all the filter is in place I open the outlet valve, making sure the outlet in the tank is not submerged. Then I open the inlet valve and, providing that pipe already full of water, the filter will fill and eventually you will see the water rise up the outlet tube. Only then do I turn on the power. I don't need to use the priming pump, I think this is only if the inlet tubing had no water in it. The priming pump does help to clear block air bubbles though and I pump until little or no air is pumped into the tank.
Those are my initial thoughts.
Ps I once assembled the filter after maintenance, filled the filter and tubing with water. No joy. I had left the impeller by the sink. Dhhh!
Sent from my iPad using Aquarium Advice
