  Observed temperatures of transiently accreting neutron stars in the quiescent
state are generally believed to be supported by deep crustal heating,
associated with non-equilibrium exothermic reactions in the crust.
Traditionally, these reactions are studied by considering nuclear evolution
governed by compression of the accreted matter. Here we show that this approach
has a basic weakness, that is that in some regions of the inner crust the
conservative forces, applied for matter components (nuclei and neutrons), are
not in mechanical equilibrium. In principle the force balance can be restored
by dissipative forces, however the required diffusion fluxes are of the same
order as total baryon flux at Eddington accretion. We argue that redistribution
of neutrons in the inner crust should be involved in realistic model of
accreted crust.
