Phenomenon: 

1. The water level of steam drum is lower than normal value. 

2. The negative value of indication of the water level gauge of electric contact increases. 

3. The alarm of low water level alarms and the signal light of low water level lights. 

4. The flow of feed water is abnormally less than that of steam( it is reverse when boiler tube bursts).

5. The temperature of superheated steam rises. 

Causes: 

1. The automatic regulator for feed water is in malfunction, and the feed water control device is in failure. 

2. The indication of water level gauge, steam flow and feed water flow indication are not correct, the operator misjudges and makes wrong operation. 

3. The feed water pressure rises or the water feed pump is in failure. 

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

5. The water wall tube and economizer tube leak or cracks. 

6. The operators are careless and did not sufficiently monitor the water and did not adjust in time or makes wrong operation. 

4. The boiler load sharply rises.

 Treatment: 

1. When the boiler steam pressure is normal, the water supply pressure is normal and the boiler steam drum water level is lower than -50 mm, the correctness of water level meter of the electric contact shall be verified. When necessary, the water level gauge shall be flushed. 

2. If the automatic regulator for feed water is in failure , the feed water shall be manually regulated. If the control device of water supply is in failure, the bypass or standby pipelines shall be switched to appropriately increase the water-feeding amount. 

3. If the water levels continues to decline, and to - 100 - mm, in addition to continuing to increase the water supply, it is required to check whether the blowdown valve and the water discharging valve are closed or not, when necessary, the evaporation capacity of boiler may be appropriately reduced. 

4. If the water pressure declines due to the low pressure of feed water, it is required to inform the person on-duty for the steam turbine to increase the pressure of feed water. If the pressure of feed water cannot be recovered quickly and the water level of steam drum continues to fall, the evaporation capacity of boiler shall be appropriately reduced. 

5. If the water level of steam drum continues to decline and disappears from the water level gauge, the boiler shall be damped down and water shall be continued to feed to the boiler. 

6. Due to the operation staff's negligence, the water level disappears from the water level gauge of steam drum and cannot be ascertained in the water level gauge of the electric contact, it is required to immediately stop feeding water to the boiler and to shut down the boiler in emergency. After the boiler is shut down, it is required to turn off the valve of the steam side and separately turn on the valve of the water side of the steam drum water level gauge. If the water cannot be supplied, it is forbidden to feed water to the boiler. After the water is fed to the boiler, if water occurs in the water level gauge, the water feeding to the boiler can be increased and pay attention to the recovering of water level. 

7. After the fault has been cleared, recover the operation of boiler unit as soon as possible. 

Prevention for overflow of Boiler: 

1. Continuously monitor each water level gauge, regularly compare and verify the correctness of each water level gauge and flush the water level gauge. 

2. When the load changes, adjust the water level timely. 

3. Regularly check the feed water regulating device, which shall be sensitive and reliable. 4. If the feed water pressure is low, it is required to contact with the operator on-duty for feed water to increase the pressure. 

5. When water is required to feed to the boiler that has been shut down due to working, it is required to pay attention to the pressure of feed water of the boiler in operation.

6. The blowdown of boiler shall be strictly carried out in accordance with the regulations of emission.