  We analyze the consequences of dissipative heating in driven Kerr
microresonators theoretically and numerically, using a thermal Lugiato-Lefever
model. We show that thermal sensitivity modifies the stability range of
continuous wave in a way that blocks direct access to broadband frequency-comb
forming waveforms, and we propose a deterministic access path that bypasses the
thermal instability barrier. We describe a novel thermal instability that leads
to thermooptical oscillations via a Hopf bifurcation.
