1. Bed temperature rise sharply.
2. Oxygen instructions decreases even to zero.
3. The  current of primary fan decreases, the air pressure of the air chamber is high.
4. The negative pressure of the hearth is increasing, the current of the induced draft fan is decreasing.
5. The slag is difficult to discharge or the slag cannot be discharged.
6. If coking happens due to low temperature, then the bed temperature and bed pressure are not evenly distributed,  the deviation is too large. The bed pressure, air chamber pressure and bed temperature are not normal, the partial bed temperature measuring point is abnormally raised or lowered.
7. The bed pressure indicating value fluctuation is small.    (lsh)