Molecular fluorine, F2, is nonpolar, the net dipole moment is zero. Molecular HF (a gas) is polar. The electronegativity difference is 1.78. There is a significant dipole moment.
It is important to understand that a molecule can be nonpolar, even if the bonds are polar. The net dipole moment is the vector sum of the individual bond dipole moments, and it is possible for the bond dipole moments to "cancel out" leaving a net dipole moment of zero (nonpolar).
Such is the case with carbon dioxide, a linear molecule, O=C=O. Each C=O bonds is polar, but the vector sum is zero, hence it is nonpolar.
..← → ............. these two dipole moments cancel
↑ /...\ ↑ ....... the two bond vectors, resolved in to perpendicular components
The "vertical" components add, while the "horizontal" components cancel. This leaves a net dipole moment on water pointing from the center of the hydrogen atoms through oxygen