Make sure the lid is closed properly and the permanent anti-grease filter is not saturated. To clean the anti-grease filter, remove the lid, and then clean the lid and filter with hot water and dishwashing liquid.
For HD4282/83, make sure the lid is closed properly. Replace the carbon filter if it is saturated.
For HD6118, HD6120-21-22-32-24, HD6140-41-42-43-44-45-46-47, HD6150-50, HD6152-53, HD6154-55, HD6156-57, and HD6158-59, check whether the sealing ring around the inside of the lid is dirty or worn. If the ring is dirty, clean the lid in hot soapy water or in the dishwasher. If the ring is worn, get a new ring.