The maintenance requirements of solar domestic hot-water (DHW) systems depend on system reliability. In this paper, the reliability of five generic solar DHW systems, which are typical of those installed throughout the United States, is assessed. Reliability block diagrams are used to evaluate the following conditions: freezing, overheating, and lack of hot water. The minimum instrumentation needed to verify system performance is described. Recommendations are presented for designers and manufacturers of solar DHW components and systems.