Expect the technician to start with power and controls before the burner: thermostat wiring, switches, and the safety devices that shut a system down. On oil equipment they'll usually look at the fuel supply, filter, nozzle, and ignition; on MGED gas equipment, the igniter, flame sensor, and venting. Plenty of visits end with a repair, and some end with a recommendation to replace.
Replacement brings Middleborough paperwork with it. Gas work is permitted through the Building Department, where the Plumbing and Gas Inspector works, and a new oil burner or tank needs the Fire Department's permit. Ask whether the contractor can set up temporary heat while permits are filed.
One local wrinkle: if an oil or propane system fails beyond repair, switching to MGED gas isn't a fast way out. New gas heating connections have been on hold since February 2019, and the town's December 2024 update reported the moratorium still in effect.