My sump pump pit was almost full of water and the pump did not extract it as usual. I lifted up the float manually and it did pump and discard a large amount of water about three or four times. Then the water it pumped would flow back, and the pump just expelled it back into the pit. I came back two days later and the same thing happened. I am not very familiar with sumps, so I certainly appreciate any help or ideas. I have only had this pump a few months although I think it was used when I got it.