Below we have provided a few checks that will enable us to either establish a fault or fix any issue you are currently experiencing:
Important: Disconnect mains electricity supply before handling or attempting maintenance. Always fully read and check the troubleshooting section within your product instruction manual. 

Please ensure the impeller underneath the guard on the underside of the motor head is not blocked, clogged, damaged or unseated in anyway. Ensure that the plastic propeller part of the impeller is attached to the magnetic body part and that they have not come apart or split. If these parts looks fine and there are two rubber grommets fitted on each end of the shaft, or already inside the fittings, then re-assemble the unit.  

Please ensure the trays are not over stocked. Once this is complete please then follow the below instructions;
  • The plastic pipework and screw-heads attached to the green pipes are tightened and fully connected;
  • The tap connections are tightened and correctly installed;
  • All black pipework is fully submerged in the fish tank. The water level must be high enough to fully cover the inlet and outlet pipes and any joints;
  • The tap is fully inserted into the filter before opening the tap and locking in place;
  • The filter is located underneath the fish tank with the green pipes as straight as possible minimising any bends;
  • When compressing the large button on the filter is there any water movement? You can test for suction by placing your finger underneath the black plastic inlet pipe in the water;
  • Prior to priming, please ensure the filter is filled as high as possible with aquarium water for ease of use.
If you follow the above instructions, you should feel some suction. It may be necessary to firmly press the plunger down a few times to get the priming function flowing. Once this has begun, you should notice your pipes filling with water and the filtration process will initialise.  
The video below will also assist if you are still experiencing issues; 

Video help guide click here