Are your tubes kinked or crooked at all? I have Fluval 404 & it is a PITA to start back up despite the self-priming. I've found if you hold the tubes straight (not crooked, etc) while the water is going into the canister, it will start up right away. By doing it this way, I found out you don't really even need to use the primer. I've also heard of people tipping it upside down for a few seconds so gravity to kick in .........