The paper is devoted to the stability of stationary solutions of an evolution system, describing
heat explosion in a two-phase medium, where a parabolic equation is coupled with an ordinary
differential equation. Spectral properties of the problem linearized about a stationary solution
are analyzed and used to study stability of continuous branches of solutions. For the convex
nonlinearity specific to combustion problems it is shown that solutions on the first increasing
branch are stable, solutions on all other branches are unstable. These results remain valid for
the scalar equation and they generalize the results obtained before for heat explosion in the
radially symmetric case [1].