If the pilot light on my furnace goes out, will the gas be shut off?

Yes, if the standing pilot light on an older furnace goes out, a vital safety device called a thermocouple immediately detects the drop in temperature because it is no longer being heated by the flame. As the thermocouple cools down, it ceases generating the tiny electrical current required to keep the safety magnetic valve open, causing the gas supply valve to snap shut automatically. This essential safety feature prevents raw, unburned natural gas or propane from continuously flowing into your home and creating a severe explosion or asphyxiation hazard. Once the gas is shut off by the safety valve, you can attempt to relight the pilot following the manufacturer's instructions. You can verify that the safety valve is working properly if you cannot smell raw gas pooling when the pilot light is out.