That can be a problem with the pressure chamber, the membrane might be warped or the micro switch may be defective. Open the lid and remove the motor and presure chamber. Inspect the unit for damages or any broken pieces. Check that the membrane is not warped. This can be tested manually by placing the motor on a work bench and putting pressure on the membrane to manually start the pump on and off. If parts are needed you can buy them through Saniflo directly. Their website is www.saniflo.com