Defro Low‑Temperature Operation / Tar Formation

Strong tar or creosote smell around furnace and in boiler room

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.

Possible Causes

Operating boiler at too low temperature, Wet wood or low‑grade fuel, Poor chimney draft, Inadequate return temperature protection

Safety: Tar deposits are flammable. Avoid open flames near the boiler room.

Increase the boiler set temperature to the level recommended by Defro for your fuel type.
Use only dry, seasoned wood or certified pellets/coal as specified.
Ensure the mixing valve maintains adequate return temperature.
Have the chimney and flue cleaned to remove existing tar deposits.

Severe tar buildup requires professional cleaning and may damage the boiler if not addressed.

Medium 3/5

Three‑Way Mixing Valve

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