Impeller loose on shaft. Disconnect power, remove pump from sump and observe for freedom of impeller and shaft rotation. Tighten fasteners, replace key as required. Clogged or damaged impeller. Remove screen and observe condition. Clean volute and impeller and remove any blockage. Return pump to Authorized Service Center. Water inflow excessive. Observe source and amount of water inrush. Have larger sump and/or pump installed. Clogged screen or pump inlet. Examine and observe. Clean screen. Air locked or air bound pump. Air bleed hole blocked. Remove pump, disconnect power, connect to rated voltage and actuate control switch. Clean out air bleed hole or drill a 1/8" or 3/16" air bleed hole between pump discharge and check valve if required. Pipe discharge closed by obstruction or ice. Examine and observe. Clean or snake discharge line. Inadequate discharge pipe diameter. Measure discharge pipe and compare with manufacturer's suggested diameter (should be no smaller than pump discharge). Have larger diameter discharge piping installed. Defective, inoperative check valve or installed in wrong direction. Observe arrow on check valve indicating direction of flow, install check valve in opposite direction if required. Check and clean gate of check valve. Loose shaft coupling. Disconnect power, remove pump from sump and observe for freedom of impeller and shaft rotation. Tighten coupling and set screws. Too high a static and friction head. Measure vertical portion of discharge pipe (over 15 feet is excessive). If discharge pipe length is extremely long, the friction losses may exceed pump capacity. Observe number of pipe fittings and reducing bushings. Remove any reducing pipe fittings and elbows. Have higher head pump installed. Have larger diameter discharge piping installed. Motor running backwards. Disconnect power, remove pump from sump. Energy pump and observe impeller and shaft rotation. If single phase unit take pump to an Authorized Service Centerbserve for correction. If three phase unit have electrician reverse rotation by inverting two of the three power cables. Sump bottom soft and muddy. Evacuate sump. Clean sump. Improperly sized pump. Observe source and amount of water inrush. Have larger pump installed.