Covalent bond is a strong bond compared to Ionic Bonds but Ionic Compounds have higher melting and boiling points then covalent compounds. Why?
When a substance is made of molecules, these molecules are made of atoms being strongly attached to one another. But a given molecule is not attached to its neighbor by strong bonds. On the contrary, they are attached by so-called van der Waals forces, which are rather weak. If you heat such a substance, the van der Waals forces are easy to destroy, and the substance melts easily. In the liquid, the covalent bonds are not modified.
When a substance is made of ions, the ionic bonds may not be as strong as covalent bonds. But they are stronger than van der Waals forces. This is why the ionic substances are melting at higher temperatures than substances made of pure covalent molecules.