1. On DCS frames, the alarm of "Air pre-heater fires," "Air preheater accident trips" is given.
2. The main motor of preheater trips, the auxiliary motor is not interlocked and started or trips after it is connected and started.
3. The corresponding gas and air baffle is closed in succession, the bearing temperature on DCS frame alarms, the current of air preheater increases and swings abruptly before tripping.
4. The negative pressure of hearth layer and gas duct swings violently and often smokes.