Performed single system heating maintenance. Replaced the 16 x 25 x 4 filter provided by customer. Removed and cleaned flame sensor. Inspected electrical connections and components. Serviced pressure switch tubing and orifice. Cleaned furnace with sanitizer and towels. Inspected heat exchangers and flue piping. At this time the furnace is operating quite well. Inspected the thermostat for functionality, and to make sure buttons work properly. System is heating as it should.