Microwave open close door error

Out side vent was allowing cold air in microwave. We do have the appropriate flapper vents installed inside the wall but they are not air tight. You could add some weather stripping to flappers as well.

[@Fetherko]

This is a strange error. I heard the fan buzzing before the microwave got the error. Other internet searches say to clean the grease filter. KZbinrs say to clean the door closed sensors. I am confused and making oatmeal on the stovetop until I fix this. thanks