The breakdown of a water film motivated by steam flow and the subsequent stability of the dry patch formed have been studied experimentally in the presence of a temperature controlled heat source enabling stable dry patches to be maintained indefinitely without overheating. Nucleation is the main thermal instability and under certain conditions will cause dry patches. Solids are deposited on the heating surface during the nucleation process which appears to inhibit subsequent film breakdown and dry-patch formation. Hydrodynamic forces are shown to govern dry-patch stability criteria; in particular the effect of surface waves, hitherto neglected, is found to be important.