rust stains on roof

mgaa

Hello, I have a red rust-like stain on my asphalt roof shingles from ridge to gutters around the chimney. I have stainless steel chimney and aluminum flashing and I have been told they dont rust. I think it may be the furnace exhaust. I have an 18 year old Burnham oil furnace and boiler. The furnace was cleaned and we found no rust. My oilman claims everything is normal. Another said its the sulfur in the fuel but I find that hard to understand. Its so strange that no one can tell me where its coming from.

Does anyone know what could be causing this stain?
Thank you

kendicanio

i have heard its the dye that is put in home heating oil to distinguish it from #2 oil that trucks can use

inspects

With two dissimilar metals, even when one of them is stainless steel, electrolysis is created and corrosion follows.