1. When the water wall pipe, superheater pipe, economizer pipe and boiler main steam pipe, water supply pipe leak. 

2. When the boiler wall cracks and has danger of collapse or the beam burns red, the wear-resisting castable inside the boiler falls off or sags, and the heating surface tube is directly worn. 

3. When the boiler steam temperature exceeds the allowable values and still cannot be recovered normal after adjustment and loading down in many ways. 

4. When the boiler feed water, boiler water or steam quality are below the standard seriously and still cannot be recovered normal after adjustment and disposal in many ways.

5. When local coking in the fluidized bed or lower part coking of the return feeder cannot be handled and the operation is hard to maintain. 

6. The coal feeder is in failure and the bed temperature cannot be maintained. 

7. When the vibration value of the blower exceeds the specified value and is still ineffective after adjustment and disposal in many ways. 

8. When the pipeline, valve and flange of the water supply, steam, blowdown and drain system seriously leak and cannot be handled during operation. 

9. When the relief valve acts and does not back to it seat; after many times of handling, it is still not effective. 

10. When the slag discharging pipe is blocked, and cannot be solved after many times of effort, and the differential pressure of materials layers exceeds the limit value. 

11. When the hydraulic components are opened, the welded joint cracks or the pipe valve leaks outwards.