Since the dipole moment of Ethyl Fluoride and Hydrogen Fluoride is same, its not of concern here, but rather only van der waals forces which depend mainly on the size of the molecule
The strength is based on intermolecular interactions.
Ethyl Fluoride is nonpolar and have very weak interactions between the molecules resulting in a low boiling point.
Hydrogen Fluoride forms hydrogen bonding which is harder for it to break apart because the bond are stronger. Resulting that the HF boiling point is much higher.
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Naga Ramesh

IIT Kgp - 2005 batch
						

							
Ethyl fluoride is indeed polar, contrary to what is said by Naga Ramesh, and can be a hydrogen bond recipient.  But there is no hydrogen bonding between molecules of ethyl fluoride like there is between molecules of HF.  Hydrogen bonding is responsible for the greater boiling point of HF.