  By considering a solvable driven-dissipative quantum model, we demonstrate
that continuous second order phase transitions in dissipative systems may occur
without an accompanying spontaneous symmetry breaking. As such, the underlying
mechanism for this type of transition is qualitatively different from that of
continuous equilibrium phase transitions. In our model, the transition is
solely a result of the interplay between Hamiltonian and dissipative dynamics
and manifests as a non-analyticity in the steady state $\hat\rho_\mathrm{ss}$
in the thermodynamic limit. Expectations of local observables are continuous
but typically with discontinuous first order derivatives in agreement with
second order phase transitions. While the model, a large number of driven
two-level systems under collective dissipation, is in some sense fully
connected, mean-field results are incapable of capturing the full picture.
