This study presents an analysis of coal switching impact by using 3500–4300 kcal/kg of calorific value (plant design more than 4500 kcal/kg) through power plant performance. It aims to investigate changes in thermal efficiency and reliability of main equipment in the boiler and optimize fuel cost by determining the cheapest coal for the power generation process. The research has been done based on a 340 MW subcritical coal-fired power plant model and experimental test with five different types of coal. Furthermore, critical equipment identification and component reliability were analyzed by calculating the boiler system's Asset Criticality Ranking value. At the same time, Reliability Block Diagrams (RBD) were also simulated based on five years of historical failure data. The results show that thermal plant efficiency decreases 0.13% in line with decreased coal calorific value every 97 kcal/kg. The optimum calorific value for the electricity production process is between 4200 and 4300 kcal/kg. The critical component of the boiler equipment is the mill, with an average ACR value of 7.81. The five mill components with the lowest availability values based on RBD analysis are Coal Pipe, Damper, Lub Oil Station, Pyrite Gate and Swing Valve with values of 0.648, 0.74, 0.91, 0.922 and 0.881, respectively. The coal calorific value has a significant influence on the efficiency and reliability of the boiler so that proper maintenance activities are needed to avoid more severe damage.