How to compare the boiling point of water, ammonia and hydrogen fluoride?
Though ammonia has three H atoms, it is not capable of forming four H-bonds

An important difference in terms of hydrogen bonding between ammonia and water, lies in the ratio between how many partial positive hydrogen atoms and how many lone pairs of electrons each have.

A water molecule has two partial positive hydrogen atoms and two lone pairs of electrons located on the oxygen atom. This implies that each water molecule can potentially have both its hydrogen atoms and both its lone pairs involved in hydrogen bonding.

But in ammonia, there is a shortage of lone pairs on the central nitrogen atom.
Hence it is capable of forming only two H-bonds.

And the difference in electronegativity is higher in $\ce{HF}$ than in $\ce{NH3}$.

Hence boiling point order is $\ce{H2O} &gt; \ce{HF} &gt; \ce{NH3}$