Some of the most common gas furnace repair issues include a thermostat failure or an improperly set thermostat. Tripped circuit breakers or blown fuses may cause a furnace to stop working as well, but are easy to fix. Air filters can become dirty and clogged over the course of time, resulting in a reduction of the gas furnace’s heat output. The furnace filter should be cleaned or replaced on a regular basis. In some cases, the blower motor may malfunction. This malfunction can cause the gas furnace to turn off and on irregularly, or to turn on too often. A faulty fan control switch may cause the fan to blow continuously.