Does it respond to speed changes and adjustments on the controller otherwise? Do you see any sign of water damage to the end connection or is the potentiometer on the junction box turned down. Also, verify that it is running and not just turning on once every 20 seconds for "fish care". A pump made prior to Sept 2011 will run for a few fell revolutions every 20 seconds, newer pumps will just twitch a half turn about and this is far less perceptible. This is a standard feature designed to keep animals out of the pump during foodtimer or other programs where the pump is resting.