  The question whether the mixed phase of a gapless superconductor can support
a Landau level is a celebrated problem in the context of \textit{d}-wave
superconductivity, with a negative answer: The scattering of the subgap
excitations (massless Dirac fermions) by the vortex lattice obscures the Landau
level quantization. Here we show that the same question has a positive answer
for a Weyl superconductor: The chirality of the Weyl fermions protects the
zeroth Landau level by means of a topological index theorem. As a result, the
heat conductance parallel to the magnetic field has the universal value
$G=\tfrac{1}{2}g_0 \Phi/\Phi_0$, with $\Phi$ the magnetic flux through the
system, $\Phi_0$ the superconducting flux quantum, and $g_0$ the thermal
conductance quantum.
