The friendliest place on the web for anyone with an interest in aquariums or fish keeping!
If you have answers, please help by responding to the unanswered posts.
Have you taken the pump apart and cleaned out the propeller area? The bottom part of the pump slips off (black part) inside is a yellow casing if you pull that off you should be able to clean the propeller area with a q-tip .. Possible it's full of gunk and not siphoning the water.
Can you send a pic of your pump? You may have to slide the bottom off but pry it open with something first ..it may be tight as its never been removed ...send a pic if you can