A gas furnace will not provide you with that soothing heat you seek in the midst of a cold snap if the pilot light cannot be ignited. The cause behind this problem can vary, but the solutions are well within the range of the average homeowner. As long as you have a collection of basic tools at your disposal, you can easily get your pilot light back on track.
Remove the access panel to see the burners. Turn off the gas to the burner at the main gas valve by turning it to the "OFF" position. Switch off the power at the main service panel or switch it off at the unit disconnect switch. Allow 30 minutes for the metal parts to cool if the burner had been running until the pilot flame went out.
Disconnect the nut holding the thermocouple tube to the combination control unit of the heater located above the tube using a small wrench. Steady the gas line that connects the pilot to the combination control with pliers. Take care not to damage the line.
Loosen the nut that fixes the pilot gas line to the combination control with a wrench. Remove the bracket that holds the pilot and thermocouple assembly in place with a screwdriver. Remove the pilot nozzle from the bracket by unscrewing it and pulling the pilot nozzle free.
Brush away dirt from the pilot nozzle using an old toothbrush. Extricate deposits that have built up inside the pilot nozzle using a piece of thin wire. Be careful not to damage the pilot in the process.
Reassemble the pilot assembly and reinstall it inside the burner. Turn on the gas and the electrical power to the furnace. Relight the pilot light to see if cleaning it solved the problem of the flame not igniting.
Turn the gas and electrical power off again if cleaning does not result in the pilot light coming on. Remove the access panel. Disconnect the thermocouple from the combination control with your wrench.
Use fine-grit sandpaper to clean the end of the thermocouple. Be gentle, but remove any ash or debris that has collected on the end of the thermocouple. Reattach the thermocouple.
Turn on the electricity and the gas supply and try relighting the pilot again. If the pilot fails to light or stay lit, remove the thermocouple once again. Take it to the hardware store to get a duplicate replacement. Install the thermocouple in place and try the pilot light again.