Usually, when you ask a furnace service company for a tune-up, you get a good inspection and maintenance service. That service checks out a lot of the critical components of the furnace and does some minor service on them to ensure that the parts are working together efficiently and safely. The technician might clean the burner assembly and make some adjustments to it. The technician might check the filters and see if they need to be cleaned or replaced. The service checks for leaks in various places, especially around the heat exchanger, which is a critical component. If that has a problem, it can be a danger. The service also checks the blower belt and motor, does some lubing of various moving parts, and makes some checks to see if the system is working actively.