  We investigate the effect of the thermal imbalance on the structural
stability of the magnetohydrodynamic model of the preflare current layer
(Ledentsov, Sol. Phys. 296, 74, 2021). The piecewise homogeneous model of the
current layer is supplemented by a magnetic field longitudinal with respect to
the direction of the current. It is shown that the presence of a weak
longitudinal field does not change the previously calculated spatial period of
the thermal instability in the most expected range of the parameters of the
preflare current layer and, moreover, contributes to the formation of the
instability. On the other hand, a strong longitudinal magnetic field
contributes to the spatial stabilization of the current layer.
