In order to study heating phenomena with submicrometer spatial resolution, we have implemented a scanning Joule expansion microscope (SJEM). When compared to scanning thermal microscopy (SThM), which requires the microfabrication of thermal probes, SJEM has superior spatial resolution and can be implemented more easily since no special tips or cantilevers have to be fabricated. Our SJEM measurements on small gold wires reveal that electrostatic force interactions between sample and tip can strongly affect the SJEM images. Therefore, we have identified the relevant parameters, in particular the cantilever stiffness, which have to be optimized to obtain reliable results. The temperature profile in the gold wires can be fitted to theoretical model calculations.