I just purchased the Tunze Osmolator 3155 about a month ago, and it has been in use less than that time, all of a sudden I am experiencing an issue. when the water gets low, the pump is turned on and the motor can clearly be heard running, however the impeller does not spin correctly. I have tried the upside down trick and removing air bubbles to no avail. The impeller moves a bit, but not enough to draw water.