If your furnace is not functioning properly, there are a number of things that could be wrong. If it's cold outside, it's something you should try to troubleshoot right away to prevent other problems such as freezing pipes or it getting too cold in your house to stay there. Read on for a few troubleshooting tips to help you make the repair on your own.
Go to your thermostat to see if you can make an adjustment to it and turn on the furnace by changing the temperature. If raising the temperature doesn't signal to the furnace that it should start and you don't hear the thermostat making any noises, the thermostat may be to blame. If it's a digital thermostat, you can sometimes hear a click when it is signaling the furnace. If you don't hear anything at all coming from the thermostat, try changing the thermostat with a new one. To replace the thermostat, turn the power off to it, then remove the cover gently so as to not pull out the wires. Look at where the wires are placed in the thermostat. Remove the wires from the thermostat and mark them with different colors of tape. Replace the wires in the new thermostat the same way you removed them from the old thermostat, then attach the cover to the wall. Add batteries to the thermostat if necessary. Turn the power back on and see if this turns the furnace on. If you are apprehensive about changing the thermostat yourself, you can call an HVAC repair technician to help you with this.
Another common problem that causes the furnace to not turn on is a cracked heat exchanger. If you have this issue, you may have had a signal from your CO2 alarm. If you don't have this alarm in your home, you should get one. A cracked heat exchanger could be causing CO2 to be entering your home and could spell disaster. If you have a cracked heat exchanger, some other signs could be a foul odor or a yellow flame instead of a blue one in your furnace. If you have a cracked heat exchanger, you should call a repair technician right away for help. Turn the furnace off completely and wait for help to arrive.
If you have issues with your furnace, call an HVAC technician who provides furnace repair services in your area.