Take the pump apart and soak it in vinegar. They have a tendency to scle up. I have all of my pumps on a regular cleaning schedule for that reason. After it has soaked for about an hour, just use a tooth brush to clean up the left over junk on the parts and in the impellor cavity. You may also have to take the impellor off of the shaft and soak it. A little bit of "stuff" in there can cause it to bind up. You can also get replacement impellors for it as well.