By Sandy Flores

You’ll be left in the cold—but not if you know how to change its thermocouple. This is the part of the furnace that shuts off the gas if your pilot light goes out, preventing that gas from seeping into your home. (You know, the gas that can kill you if left to run amok.)

If the furnace won’t stay lit, there’s a good chance you have a faulty thermocouple. Learning how to replace or adjust yours can be the difference between a $10 trip to the hardware store, and a $90/hour visit from a technician. Most thermocouples are held in place by brackets, which can be gently unscrewed to insert the replacement thermocouple.

Keeping a spare thermocouple on hand during winter is especially smart, because furnace problems can be more inconvenient—and costly—during the peak times of the year.