Not all furnaces have a flame sensor, but if your furnace has one, it will be mounted close to the burner with the metal rod positioned in the flame. Flame sensors vary in size (2 to 4 inches) and shape (see examples below).Click to see full answer. In this way, are furnace flame sensors universal?Universal flame sensors: You might not need an exact replacement part. Universal sensors are available too. They are available at your local Home Depot, Menards or other building supply store. Video tutorial: This video from a Canadian supplier shows how easy it is to locate, remove and replace a flame sensor.Also Know, can you bypass the flame sensor on a furnace? Actually, you can bypass the flame sensor. the flame sensor is just a way of exposing the voltage on the flame sensor wire to the furnace burner flames. So you can connect the flame sensor wire to a screwdriver and put the screwdriver into the flames. Then, how many flame sensors does a furnace have? A Wire in the Furnace Leads to the Flame Sensor This furnace has four burner ports. Between the first and second burner ports (from left to right) you can see the wire leading to the flame sensor.How do furnace flame sensors work?How A Furnace Flame Sensor Works. A furnace flame sensor works by detecting the presence of a flame within the furnace. As the gas valve opens to begin the combustion process, the current is sent out from the sensor in order to detect the presence of heat from a flame.