No, you should
not use diesel fuel in a heating oil system. While they are similar, they have different chemical compositions and additives. Using diesel in a heating oil system can cause significant damage to the fuel pump, injectors, and other components. It can also lead to clogging and poor combustion, resulting in expensive repairs or even system failure. Using the wrong fuel will likely void any warranty.
Stick to using the fuel specifically designed for your heating oil system.
