Fluval 305 Filter Problems!

OK, bear with me, I don't have any externals, but I know a bit about them and I've just downloaded the manual to take a look.

It says you fit everything together, sort out the tube lengths etc. I assume you've done all that.

Have you connected the tubes the right way round?
Have you locked the aquastop valve in place and opened it?
Have you pumped the priming handle up and down till you heard water going into the filter then pushed the prime handle down?
Have you watched the water flowing into the filter and pushing bubbles through the tube and out into the tank water?
Did you do all that before plugging it in?

From what I can gather from reading elsewhere, the main problems seem to be connecting the inflow pipe to the outflow hole, and having air trapped. If you did everything the manual says, try tilting the body of the filter from side to side to expel any trapped air.


Other than that, I don't know what to suggest 

Is it a new filter or second hand? I've heard good reports of Hagen's customer service (they make Fluvals)