DIAGNOSIS The water level sensor (a float switch) is stuck in the 'low' position, or there's a blockage preventing water from reaching it.
FIX Unplug the unit. Gently slosh the water in the reservoir back and forth to try to free the float. You can also try tilting the whole machine slightly side-to-side. If that doesn't work, empty the water, unplug, and look for the float—usually a small white plastic cup—inside the water tank. Manually move it up and down a few times to ensure it's not jammed.
IF THAT DIDN'T WORK There might be debris or scale blocking the inlet where water flows from the reservoir to the pump. You'll need to partially disassemble (often by removing a few screws on the base) to check the water pump inlet filter, if it has one.
HEADS UP Using distilled or filtered water isn't just for better ice—it prevents the mineral buildup that gums up these small float mechanisms and sensors.