I grew up in a house that was in my dad's family for 3 generations, his grandparents were the first to live there. Anyhow, when I was in college, my family was getting ready to move, and we woke up one morning to a cold house. We figured we had run out of oil for the furnace (which had happened a few times throughout the years.) So my dad went to check, and there was at least a half tank of oil. So he checked the furnace to see if the pilot light had gone out, or if it was otherwise not working, but it appeared to be fine. (My dad is a jack of all trades, carpenter, mechanic, mr. fix it, etc., so he knows about all these things.) His last thought was that there was a clog in the line between the oil tank and the furnace, which were both in a little old back room of our basement, where we rarely went for ANYTHING other than to do anything with the furnace, really. So in order to check the line, my dad said he would have to shut off the valve on the oil tank... so he proceeded to try to close the valve... and it was locked solid. He figured it was just stuck from having not been touched in many years. After several attempts to close it, without it budging, he finally realized that the valve WAS ALREADY CLOSED. And closed so tightly, he had to hold the valve with a wrench and bang it open with a hammer to get it back open. Me, my mom, and dad were the only people living in that house, and we had no visitors on that night. My dad asked me and my mother whether we had closed that valve, and of course, we had not! Neither my mother nor I would have even known where to look if my dad had told us to close that valve, let alone either of us having shut it off without being told to or without some reason to do it! The oil tank was tucked back in the corner of that room no one ever went in, and the valve was on the end of the tank, by the wall, so there is no way it could have been bumped closed, especially to the point that it had to be banged open with a hammer.
Someone had closed that valve, and to this day, we have no explanation as to who did it. Our only guess is that someone, most likely family, was making their presence known in light of the fact that we were about to move out of the family home...