S06E10 Grampa vs. Sexual Inadequacy
Grampa invents an aphrodisiac tonic,which kick-starts the sex lives of most of the adults in Springfield and he and Homer go on the road to sell it. However at an old farm-house where the Simpsons once lived,Grampa reveals to Homer that his birth was accidental. Homer is angry and the two part. But after reflection,they reconcile back at the farm-house but also manage to burn it down.