We just bought a Polaris 280 about a month ago. It was working fine, but for the past 2 weeks it gets stuck on our steps and literally will stay there the entire time it is set to run. The back up valve is working as I have checked it many times and it will pull the Polaris out of other parts of the pool ( after I have pulled it away from the steps). Also the wheels are rotating within the right rpm. The hose length between the polaris and the back up valve is 3 feet. Is that too long? Any other thoughts/suggestions?