The igniter, flame sensor and high-limit switch are the parts of a furnace that can be replaced. Other replaceable furnace parts include the mounting bracket, fan blade, control board, capacitor and drain pan.

A clogged furnace filter is one of the most common causes of furnace problems, and it can be fixed by replacing the igniter, flame sensor and high-limit switch. A furnace owner should study the service manual for his or her specific furnace before replacing parts, since the components of a furnace are located in different areas depending on the brand. To buy the right model of a component, the owner should read the manufacturer’s label on the side panels in the burner section and take a picture of the manufacturing date, serial number and model number.

The igniter and flame sensor are not often directly visible, because they are hidden inside a combustion chamber. The high-limit switch is typically located beneath the combustion chamber and has a flexible tubing below it.

The furnace owner should ensure the furnace power is turned off before starting any repair. Before replacing specific parts, it is necessary to check for a tripped breaker or a flipped switch, as these may be the culprit of a furnace problem. It is also crucial to change the air filter if dirty. If the furnace fails to restart after changing the filter, the high-limit switch has likely been damaged by overheating. The switch must be replaced if it’s not functioning properly.