Sounds like the motor is too small for the job.? has the motor been changed? if not -have the run capacitor checked by your local pool pump motor repair guy also the SF and HP must match the impeller size this number can be found on the front of the impeller and SF,HP can be found on the motor ID PLATE. gather all this info when you buy a motor or impeller .. very important ! . if you find you are stuck with you new motor the FIX is to get the impeller that is right for your motor