A water heater door assembly includes a base plate sized and shaped to substantially sealingly cover an access opening in a water heater combustion chamber and has at least one opening through which a fuel supply line extends at least partly between a burner in the combustion chamber and a gas control valve, and a flexible seal positioned at least partly within the opening including an engaging portion substantially sealed to an edge portion of the opening, and a through hole that is shaped to receive the fuel supply and has a size slightly smaller than the size of an outer dimension of the fuel supply line such that the flexible seal and the fuel supply line are friction fit together to form a seal.