1. The automatic adjustment of water supply fails and the adjusting device of water supply malfunctions. 

2. The incorrect indication of water level gauge, steam flow meter or feedwater flow meter makes the operator misinterpret and incorrectly operate. 

3. The failure of feedwater line and feedwater pump causes the pressure of feedwater to decrease. 

4. The boiler sewage pipeline and valve leak, the blowdown amount is too much.

5 The water wall pipe or the economizer pipe burst. 

6.The operators are negligent, they do not monitor the water level very well and do not adjust it in time or make incorrect operation.