If the bowl holds water...
Most likely it just means it's time to replace the duckbill valves in the vacuum pump.If the bowl doesn't hold water, try cleaning the underside of the opening. If that doesn't work, you may need a new ball kit. Or, you may only need to learn how to flush it correctly.The two most common mistakes VacuFlush owners make are: 1) not leaving the pedal down long enough. The pedal not only opens the hole in the bottom of the bowl, it also controls the flush water. It's necessary to leave the pedal down at least 3 full seconds after the bowl is empty, to rinse the waste out of the vacuum pump. 2) easing the pedal up instead of just releasing it. It's spring loaded for a reason--to allow the dome to snap back into place with enough force to seat it so it can seal. Easing the pedal back up doesn't let that happen, and can damage the mechanism. Just let it go...that's how it's designed to work.Just about every symptom a VacuFlush can develop, along with the probable causes and cures, is covered in the owners manual. If you don't have one, ask SeaLand to send you one when you order the duckbills (800-321-9886). And keep it on the boat where you'll have it to refer to...'cuz messing with a VacuFlush without knowing what makes what happen (and you obviously don't if you had to ask what causes it to cycle) can create bigger problems than the one you're trying to solve.