Fracture sealing through the precipitation of hydrothermal cements is an important component of some conceptual models describing the earthquake cycle. Within these models, coseismic boiling of pore fluids has been proposed as a mechanism for generating the fast cementation rates required to facilitate sealing over interseismic time scales. It remains unknown, however, whether it is possible for coseismic boiling in the crust to proceed to the extent that fractures become sealed. In this contribution, I examined whether coseismic boiling can realistically provide a mechanism for fracture sealing using the thermodynamic properties of water. The results of my calculations demonstrate that coseismic boiling is self limiting due to the establishment of equilibrium vapor pressure following earthquake rupture, and it is not capable of facilitating sealing. More specifically, results indicate that the maximum amount of water that can undergo coseismic boiling decreases from ∼115 kg per cubic meter of dilation at 350 °C down to ∼3 kg per cubic meter at 150 °C. These temperatures span the approximate range of the seismogenic crust. Additional calculations show that these relatively small masses of fluid precipitate negligible volumes of hydrothermal cement during boiling, enough to fill less than 0.005% of any dilational volume. These calculations suggest that coseismic boiling is unlikely to play a major role in fracture sealing during the seismic cycle.