A PLTU must carry out operational tasks continuously to meet electricity needs. Based on historical data PT. PJB Service Kendari for the last three years, there has been an increasing trend of downtime and derating at PLTU Nii Tanasa Kendari. The boiler system is one of the systems that often experiences disturbances. The purpose of this research is to carry out a risk analysis and improve reliability using the FMECA method and reliability calculations. FMECA is required to carry out a risk analysis to find out in detail ways of mitigating risks, sorting and labeling risks for critical components based on the RPN. The results of reliability calculations based on MTTF found that 9 out of 13 critical components had a reliability value below 50%; increasing reliability values could be achieved using preventive maintenance (Rm(t)), and maintaining reliability values above 60% could be achieved using periodic component replacement (R(t-nT)).