Follow this simple checklist:

1. Is the drain valve closed? (The small handle on the valve should be perpendicular to the direction of the drain tube.)
2. Have you cleaned the door?
3. Is the black rubber gasket (door seal) clean?
4. Have you replaced the oil in the vacuum pump?
5. Is the vacuum pump filled with oil to the middle of the sight glass?
6. Is the door closed and compressed tight?