How to get rid of these 'pseudo-planes'? 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.
I can't see a lot from your image but this might be just a big n-gon, so maybe you can try selecting these two vertices marked in red and pressing J to create a line. (it will probably solve it by completing the box shape)