hi i would get the co detector checked out it sounds like fumes to me when the guy checked out your furnace did he check the flue sonds from what your saying it may just have a crack or small hole. hope this helps you. good luck
is your house making you sick. a week in our apartment we smelled an odor. my fiance told me and our two kids to get out of the house. we went to my mom's for the night. the oil guy said the furnace hadn't been cleaned in years. 2 days later i went back. we got a co detector and a level detector that would let us know if there were any levels of co in the home. it's always remained 0. before this i was getting a cold. i have one symptom i haven't had before. burning eyes. could it be from the house?