Thermocouple Replacement Procedures

If your gas furnace, gas water heater or other gas fired unit will not keep a pilot light burning, the chances are pretty good that the thermocouple has gone bad and needs to be replaced. This is a common procedure that can be done using just basic hand tools like an adjustable wrench. They are available at virtually any hardware store, but just remember to remove the original one first so you can take it with you and match it up for the correct size that you'll need.

Getting ready

Before you do anything else, turn off the gas line feed. There will be a valve either on the control unit itself, or where the black pipe comes in from your gas source, whether it is natural or propane. Regardless of which type of gas you have, the gas MUST be turned off fully and completely before you begin this procedure. Failure to do so may result in an explosion, so better to be safe than sorry and turn off the gas line feed.

The procedure

There will most likely be a little access panel which conceals the control unit, and that panel will have to be removed before you can access the thermocouple.

There will be a screw-in nut attached to the control unit, which when tightened, secures the tail end of the thermocouple inside. This nut needs to be unscrewed, gently, using either an adjustable wrench or a wrench specifically made for that nut size.

Once it is unscrewed, pull the end of the thermocouple out of the control unit, then follow the copper tubing to where it interacts with the pilot light.

Generally, but not always, there is just a metal clip holding the head of the thermocouple in place. This can be unclipped with fingers and pulled out gently to separate it from the pilot light base.

In other types, there is a little nut that will hold the head of the thermocouple in place. If that's the case, use your adjustable wrench once again, loosen the nut and pull out the thermocouple head.

Once out and in your hands, go to your favorite hardware store, match the old one to a new one, come home and get ready to install.

Installation

Back at home, carefully unravel the new thermocouple form the package. They are all almost universally coiled up inside, so be careful when unwrapping it.

Installation is just about the same as taking it out as you'll push the end inside of the control unit that has the nut attached, then screw it in. There is no need to use force with this nut, just hand tighten it and give it a half turn with your wrench, and that's all there is to that.

If it has a nut on the thermocouple head, screw it into the pilot light base hand tight, just like the control unit, and give it a half turn with your wrench.

If it is a clip-on, the head of the thermocouple must be positively inserted into the actual pilot light flame to be effective. The attachment clip is pre-bent to allow the perfect angle at which the head will sit. just clip it on and make sure the head will sit inside of the flame from the pilot light.