Peeling of wallpaper is a very rare thing. it would happen where the adhesive used to stick it onto the wall is used in lesser quantity then required. But do not worry about it. It can easily be fixed. If its not a larger area, then you can do it yourself. For that you will require wallpaper seam adhesive, a paint brush, rug, and a wallpaper roller. You can simply pull the corner or paper till it firmly adhered to wall. Next, apply the wallpaper adhesive to peeled area. Then slowly press the wallpaper to its area and run the roller on it. With the rug, wipe out the excess adhesive. Simple!!! But places where wallpaper or Wall Covering is affected because of leakage problem then its difficult to repair. You can say its unfix-able. Also you don’t have to worry of the natural heat ( sun light ).