1. The bed temperature rises sharply.2. Oxygen levels go down and sometimes drop to zero.3. The electric current of primary air fan is less and wind pressure of air compartment is higher.4. Negative pressure of furnace is increased while the electric current of induced draft fan is reduced.5. The slag discharge is difficult or unsuccessful.6. When appearing bed clinkering, the bed temperature and bed pressure will be uneven distributed and not at normal condition; the measuring point of part bed temperature rises or falls abnormally.7. The indicator of bed pressure has a very small fluctuation.