How to Replace the Thermocouple in a Furnace

Replacing a thermocouple in a furnace is a job that can be done by anyone with basic DIY skills. If the pilot in your furnace will not remain lit and you have checked for any dirt blockage in the gas flow this would be an inexpensive repair to perform yourself.

Always shut off the electric and gas to the furnace. Shutting off the power and/or fuel supply to any piece of equipment before attempting to repair it is an important safety issue. It is, unfortunately, something many people forget.

Have your furnace manual on hand for picture references to the thermocouple and detailed steps for your furnace. If you do not have the original manual, many can be found online. Some online sources will even go into greater detail than the original owner's manual.

Having the replacement piece on hand before you begin simplifies the project. You can take the old thermocouple with you to the store to match it to the new piece but it is easier to have it already on hand. Write down you furnace make and model number and, if possible, the thermocouple part number. You will use this information to obtain the OEM or generic replacement piece.

Have your basic hand tools ready. Having to go back and forth from the furnace to your workshop, or garage, for tools only adds frustration to your project. You will most likely need a small adjustable wrench or set of small box or open end wrenches. You may also need a set of small screwdrivers, flat or Phillips, depending of the location, and installation, of the thermocouple.

1) The thermocouple is located next to the pilot light. Depending on the exact style of your burner assembly you may need to loosen or remove the assembly first.

2) Disconnect the copper lead and unscrew the gas line connection nut to the thermocouple. Unscrew the bracket nut that holds the thermocouple in place. Slide out the old thermocouple.

3) Clean the area around the pilot and bracket assembly gently to remove any dust or debris. Do not use chemicals, just lightly brush away foreign material.

4) Slide the new thermocouple into the assembly, the copper part should be facing down. Tighten the bracket nut.

5) Connect the copper end to the gas line and hand tighten the connection nut. Do not use excessive force, copper connections can strip.

6) Check your alignment. One half inch of the tip of the thermocouple should be positioned so that the pilot flame will heat it.

Once you have replaced the thermocouple, follow your furnaces instruction for relighting the pilot. Remember to turn the gas and electric back on from where you shut them off. You may consider using a soap and water solution on your gas connection to be sure you have no leaks. If replacing your thermocouple does not solve your furnace problem you may wish to call in for professional repair.

References:

http://home.howstuffworks.com/home-improvement/heating-and-cooling/how-to-maintain-a-furnace1.html
http://www.ehow.com/how_2074294_replace-furnace-thermocouple.html
http://www.acmehowto.com/howto/homemaintenance/plumbing/appliances/waterheater/replace-thermocouple.php