While many furnace repairs require expertise, some problems can be fixed using the operation manual. If the furnace uses a pilot light, for example, relighting it is fairly straightforward.
Before calling an expert, it might be worth reading through the furnace's manual and performing maintenance tasks. Simply cleaning the pilot light and gas nozzle, for example, might fix the problem. A filter that has become dirty might cause the dryer to stop working, and replacement is generally simple. Individual components of the furnace can also be tested to help narrow down possible problems. If the fan spins when the furnace is set into "fan" mode, for example, the problem likely lies with the fan, its motor or the electrical connection.