If all else fails, check the furnace’s gas valve to make sure that it hasn’t somehow been turned to the “Off ” position. Any gas furnace has a gas cock, or valve, that has to be located within six feet of the furnace, Bonner says. This is usually never touched, but you could check it. Another way to double-check: If you have more than one gas appliance, find out if it’s working. If it is, you know that the gas line into the home is OK.