Responded to service call for a 16-year-old oil furnace exhibiting smoke at the injector and continuous fan operation. Inspection revealed improper ductwork modification with return air opening directly above the exhaust baffle, causing minor sooting. Heat exchanger was intact with no internal damage. Replaced nozzle, verified proper system function, and advised customer to relocate the return air opening further downstream and properly seal existing ductwork to prevent recurrence.
