In the operation of No. 3 boiler scraper slag machine of the third thermal power plant of Yangquan Power Supply Branch, the chain broke out from the climbing guide wheel set. The boiler must be fire extinguished and repaired in a short time, but there is a burnt injury in the repair process. Hidden dangers. In response to this problem, after on-site analysis, safety measures were added to install the plug-in door at the exit of the boiler water seal shut-off board. After the implementation of the improvement measures, the problem was solved and a reference was provided for the same type of maintenance.