The demand of steam in process industries is increasing rapidly, and this demand can be met by increasing the capacity utilization of steam boilers. Many of the process industries depend on industrial steam boilers as a vital component for their operation. The availability of the boiler can be improved by identifying critical mechanical sub-systems/components concerning failure frequency, reliability, and maintainability and minimizing their likelihood of occurrences. The selection of appropriate technique for data collection and reliability analysis is essential. The time between failure (TBF) and time to repair (TTR) of all components and sub-systems were collected to carry out Reliability, Availability and Maintainability (RAM) analysis. The best-fit distribution and distribution parameters were calculated using ReliaSoft software Weibull++10 after performing trend testing. The preventive maintenance intervals of all components and sub-systems and the availability of the system were evaluated. The analysis reveals that the combustion system, feed-water system, and blow-down system are the critical sub-systems from a reliability perspective and are still the biggest reasons for the boiler downtime. The research study also showed that TTR was longer for the combustion system than the other sub-systems, and thus, to enhance its availability, it is suggested that maintenance resources should be allocated at the appropriate moment to the combustion system. The study also shows the usage of RAM analysis in deciding the preventive maintenance intervals of components/sub-systems of the boiler. It also provides a reference for the preparation of the maintenance plan for the boiler system.