* Damage to the burner: Diesel fuel has different viscosity and ignition properties than fuel oil. This can lead to improper combustion, clogging of fuel lines, and damage to the burner nozzle and pump.
* Incomplete combustion: Resulting in reduced heating efficiency and potentially dangerous carbon monoxide buildup.
* Warranty voidance: Using the wrong fuel will likely void any warranty on your heating system.
Fuel oil is specifically formulated for use in oil-fired heating systems. Diesel is designed for diesel engines and has different characteristics. Always use the fuel specifically recommended by the manufacturer of your heating system.