Never run the filter without first making sure that it is primed. Operating the filter without first priming it can lead to serious malfunctions in the unit.
In many cases, simply removing the impeller and then putting it back into position will solve the problem. A little petroleum jelly on the base of the impeller also might help resolve problems.
Fluval aquarium filters are products of Hagen, Inc. Their design consists of an unconventional flow system that uses the area within the entire canister, leading to greater flow rates and improved performance. Popular with many aquarium enthusiasts, Fluval filters are relatively inexpensive and have a low failure rate. Occasionally, problems will surface and you will need to troubleshoot the equipment. Since the filter has few moving parts, locating equipment failure causes is relatively simple.
Test the circuit the filter is plugged into to make sure it is active, because circuits with aquariums are easy to overload. Unplug the filter and plug another electrical appliance into the electrical outlet. If the electrical outlet works but the filter does not, chances are that the filter motor has burned out and needs replacement. Purchase replacement parts online or at an authorized dealer.
Check that the output tube has no kinks or bends in it. A kinked hose will prevent the water from flowing and will lead to increased pressure put on the filter.
Prime the filter. To do this, open the hinged top of the filter and pour in one cup of water taken from the aquarium. This will prime the filter mechanism, which should then start the filter flowing.
See if the filter cartridge is clean. If the water in the tank isn't clear, the filter may be dirty or the water in the tank may be "cycling." Cycling takes place when beneficial bacteria begin to build up in a tank. In most cases, the water will turn clear again in about one week.
Check the impeller assembly if you hear grinding noises from within the filter. The impeller looks like a small propeller and if it is improperly seated, it will cause a lot of noise. Open the top hinge and locate the impeller. To make sure that it is seated properly, turn it clockwise 270 degrees and feel it lock into place.