Check all hydraulic lines and fittings at both the jacks and the hydraulic manifold. I had several loose fittings that came to light after my pump burned out (attempted to retract jacks several times, but failed to retract), ended up costing me $828 dollars to replace the pump. Pretty expensive repair that I could have avoided, had I followed the trouble shooting procedures. The system is designed to retract and then basically put a vacuum pressure on the system to maintain the jacks in the up position.