Those little centrifugal bilge pumps are amazing, but they can also be touchy.
This year I saw a boat that got partially flooded due to a cracked water strainer. The bilge pump was found burned out, and at first it was believed that it burned out coping with the flood... but after the bilge pump was changed, it ran but there was no pumping. We disconnected the pump, stuck a garden hose nozzle into the out hose, gave it a blast, and after that the pump worked fine. Now the out hose was fairly long, and there was a check valve inline, but still, it didn't take much to stop that new bilge pump from working.
Moral: exercise your bilge pump so that it and the hose remain clear.