We discuss the sensitivity of a 100 TeV pp collider to heavy resonances produced in longitudinal vector-boson scattering and decaying to a pair of Higgs bosons. A Monte Carlo study has been performed using the H→ττ decay channel for both Higgs bosons, comparing the kinematics of such a signal to the irreducible Standard Model backgrounds. The results are presented in the context of a phenomenological model of a resonance (η) coupling to Goldstone modes, VLVL→η→HH, as can arise in composite Higgs models. With a fractional width of 70% (20%), the 5σ discovery reach is 4.2 (2.9) TeV in resonance mass for 10ab-1 of integrated luminosity. We also discuss the dependence of the mass reach on the collider energy and integrated luminosity.