To me the obsessive thoughts are anxiety based. As it was mentioned, a common theme is being afraid that the stove was left on and that the house will be burned down while you are out of the house. This can lead to the compulsion of needing to go back (sometimes over and over again) to check that the stove is turned off, or it can just mean that you are obsessing over that thought without doing anything about it. Still, it is generally an anxiety based thing with ocd. Like with the obsessive thought of a family member being harmed leads to the compulsive action of checking (and re-checking over and over again) on that family member to make sure that they are safe.