They should last 3-4 years, they can fail prematurely if they get wet, if the pump is jammed so the draw excedes the 50W limit of the power supply or if the power supply is operated in a location with a temperature over 80F and or over 70% humidity. My best guess is the drive unit was partially locked up by calcium, the pump uses 35W when clean at full power, this creeps up as the pump gets dirty, if the drive unit seized to the shaft, it easily peaks past 50W. The first few times it will shut off as a safety, but it cycles back on once it cools down, if unnoticed for several days, the power supply eventually fails.