If the furnace is under warranty, the best contact is in the warranty documentation. Frigidaire furnaces, for example, have a 10-year warranty on all parts when registered. If the furnace isn't under warranty, call a local repair company that is authorized to service the brand of furnace needing repair.
For people in the greater Houston area who have American Standard, Carrier, Trane, Rheem and Goodman furnaces, one local company is Stay Cool AC and Heating Services, located in the Houston suburb of Cypress. Using a company that is authorized to service and familiar with the homeowner's brand of furnace is the best way to get a quality repair job.