Three years ago, I posted about keeping your power filters clean, especially the impeller and impeller housing. The point of that post was to help you avoid filter restart problems in the event of a power outage (or when you unplug the filter when you feed your fish or some other reason). Most of the time, a restart failure is due to a dirty impeller housing, dirty impeller, dirty impeller shaft, or all of the above.
If you’re running canisters or HOBs, some brands use impellers with removable shafts. The shaft is the ceramic or metallic rod that goes through the impeller to keep it stable as it rotates. When you remove the impeller to clean both it and the housing, also consider removing the shaft and cleaning it along with the shaft channel (i.e., the hole through the impeller itself where the shaft resides). Detritus and other buildup can inhibit the impeller’s from rotation on the shaft, so it’s important that you keep it clean. A small accumulation of material on the shaft or in the channel can provide just enough resistance to prevent the impeller from turning on start-up, effectively rendering your filter useless.
Once the impeller and shaft are cleaned, reinsert the impeller back into the impeller housing. Plug the filter in to ensure that the impeller turns. You only need to run it for a second or two to know if the impeller is turning, and it won’t hurt the filter to run dry briefly.