Defro Incomplete Combustion / Sooting

Strong smoke or soot deposits visible at chimney outlet and on nearby surfaces

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Safety Warning

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

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Possible Causes

Low combustion air due to dirty fan or blocked air inlets, Excessive fuel feed rate, Poor fuel quality or high moisture content, Dirty burner pot and heat exchanger

How to Fix / Troubleshooting

Safety: Soot buildup increases fire risk. Perform cleaning only when the furnace is cold.

  • Clean the burner pot/grate thoroughly, removing all clinker and ash.
  • Brush and vacuum the heat exchanger tubes and flue passages.
  • Inspect the combustion fan and air intake openings; remove dust and debris.
  • Reduce the fuel feed rate slightly in the controller settings and/or increase combustion air within Defro's recommended range.
  • Use only dry, certified fuel suitable for your Defro model.

If heavy sooting continues, have a technician optimize combustion settings and check chimney draft.

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Repair Difficulty

Medium 3/5

Required Part

Burner Pot / Grate
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