No, not ALL HOBs -- the Aqueon QuietFlow line has an INTERNAL pump which is submerged inside the tank and water and the filter reprimes itself EVERY time the power is shut off. It's a great feature and I wish the AquaClears were like this; you state you never had to prime any of your AquaClears but I find that difficult to believe as that no matter where the water level sits upon fill up, like the other member mentioned it's a matter of these filters SITTING for one or more minutes without power/water that require them to be reprimed with water. However, my 110 model acts strangely sometimes, after some water changes starting up even though it's been longer than a minute the power is off while at other times refusing to start and making that "choking" sound that requires me to prime it...