You do know you have to prime a canister filter every time you break the suction correct? that is part of normal operation. It will not pull water in on its own without being primed. Some nicer filters have priming pumps or buttons on them to pull water in at the startup, most do not...which means generally you have to suck on the outlet to start the process. If you have a lily pipe the end of a turkey baster works well to start the suction. You should not turn your filter on until it has filled with water, it is not a dry pump and running it dry can ruin it. I do not think you have a broken filter...I think you are not familiar with how to operate a canister. I had a hell of a time when I first got a canister filter...now I'm very good at getting it primed and troubleshooting problems. When you turn it off if you have valves on the hoses you can close them and leave the filter running for up to 30 minutes and preserve the siphon. After 30 minutes you could start to do harm to your biofilter from a lack of water flow. For longer maintenance sessions you should empty the filter of water and replace the lid to maintain humidity while you do the maintenance to preserve the biofilter.