  The impact of various competing heating processes on the thermal evolution of
neutron stars is investigated. We show that internal heating leads to
significantly enhanced surface temperatures for pulsars of middle and old age.
The heating due to thermal creep of pinned vortices and due to outward motion
of proton vortices in the interior of the star leads to a better agreement with
the observed data in the case of enhanced cooling. The strong pinning models
are ruled out by a comparison with the cooling data on the old pulsars. For
millisecond pulsars, the heating due to thermal creep of pinned vortices and
chemical heating of the core have the largest impact on the surface
temperatures. The angular dependence of the heating rates require two
dimensional cooling simulations in general. Such a simulation is performed for
a selected case in order to check the applicability of one-dimensional codes
used in the past.
