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Boiler furnace blowback

Cause of Boiler furnace Blow Back

Main cause of boiler furnace blow back is accumulation of hydrocarbons inside the furnace. Hydrocarbons may exist as vapours or liquid form inside the boiler furnace. Accumulated fuel vapours inside furnace catches fire and develops high pressure inside the furnace thereby resulting in dangerous explosion. It is a usual practice that when there is frequent flame failure, operator try to fire the boiler in manual mode. In manual mode pre purging is not automatically controlled. Hence an attempt is made to fire boiler with insufficient pre purging time and eventuality may be catastrophic explosion.

Preventive Actions

  • Allow sufficient time for pre purging the furnace with dampers full open to ensure all the accumulated vapours are expelled out.
  • Purging to be carried out 5-6 times the furnace volume for effective expelling.
  • Never try to reduce purging time or bypass it.
  • Carry out boiler burner and swirler routine as per planned maintenance system.
  • Do not fire boiler with heavy fuel oil or sludge if it is not designed for the same.
  • Air fuel ratio of oil compound regulator to be adjusted correctly to maintain proper and complete combustion.
  • Pilot burner to be maintained in good condition so that flame failure while starting does not occur.
  • Igniter or ignition transformer, its leads, etc. to be properly insulated and tightened.
  • Fuel oil fed to the boiler to be properly treated as per manufacturer’s recommendations.
  • If an economizer or pre heater is fitted in the boiler exhaust, same to be water washed and inspected regularly to avoid back pressure of gases.
  • Conduct furnace inspections periodically to inspect conditions inside.
  • When a flame failure is experienced find and rectify the root cause. Do not try to fire again and again.


  1. Extremely useful information which you have shared here about furnace. This is a great way to enhance knowledge for us, and also beneficial for us. Thank you for sharing an article like this.
    Chicago duct cleaning company

  2. Should a technician check the transformer when they are cleaning the furnace?

  3. This comment has been removed by the author.


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