Phenomenon:

1. The feed water flow is abnormally greater than the steam flow, in serious case the water level of  steam drum drops. 

2. The flue gas resistance increases and the current of induced draft fan increase. 

3.The flue gas temperature of economizer and air preheater decrease and the temperature difference at both sides increase. 

4.The hearth negative pressure decreases or becomes positive pressure. Steam emits from the place of flue that is not closely sealed, in serious case, water leaks from the ash hopper at tail of the flue. 

5. There is abnormal noise inside the flue of economizer. 

6. The temperature of exhaust fume drops. 

7. Fly ash is wet. 

Causes: 

1. The economizer water temperature and flow rate change greatly and water impact is serious. 

2. It is worn by fly ash . 

3. The quality of feed water is poor and pipe is corroded. 

4. The material, manufacturing or welding of economizer are poor. 

5. The pipe is blocked by sundries, thus causing local overheating of pipes. 

Treatment: 

1. Increase the feed water to boiler, maintain normal water level of steam drum, decrease the boiler evaporation capacity, and put the standby boiler into use as soon as possible or increase the evaporation capacity of other operating boiler, in order that the boiler can  be stopped as early as possible. 

2. If the failure boiler cannot maintain normal water level or the damage of the boiler intensifies during continuous operation and affects the feed water of other operating boiler, the boiler shall be stopped immediately in order to maintain the operation of the induced draft fan. 

3. After the boiler is shut down, shut off the main valve. 

4. In order to maintain water level of steam drum, it is possible to feed water to the boiler continuously, close all the water draining valves, and it is prohibited to open the re-circulation valve of the economizer.