Taiwan Photon Source (TPS) is a newly deployed 3 GeV synchrotron light source. Reliability design have been considered at design phase. Adopt right technology, adequate redundancy, enough safety margin are used to ensure acceptable reliability. However, some subsystems inherent operate in reliable way but some not due to various reasons. The light source was operate for dry run, beam-line commissioning, and pilot experiments during March-June, 2016. User service started from September 2016. Reliability is not good during early operation. Improvement of subsystems and reduce troubleshooting efforts to minimize downtime were achieved after analysis causes of various unreliability events and to do adequate actions. Various diagnostics tools were employed to record related signals at the event happened. These diagnostic tools can capture various signals for post-mortem analysis. Lessons learned from these events teach us how to manage reliability of the accelerator system. After the efforts for last two years, reliability of the accelerator system improved drastically since operation of the TPS. Some unreliable scenarios, efforts to improve and plans for future will be summarized.