I often make small mistakes when extruding geometry for example when extruding walls for a house. Sometimes this creates double geometry. I know I can get rid of this using W > remove doubles. In this case I can't seem to get rid of this faulty geomtry (see screenshot). Somehow, these 3 vertices seem connected with a plane that I didn't create. I tried Remove Doubles, Dissolve, Delete etc... but nothing works.
Can someone tell me how to clean these problems please? Thank you.