How to repair and replace a thermocouple in the Furnace?

What is Thermocouple?

The thermocouple is a necessary part of the furnace in terms of security. A thermocouple is a small, continually burning flame. It is commonly used in the gas furnace with a standing pilot. The thermocouple's top is situated in the flame to ensure that the tip is always warm. 

When the pilot flame goes out, the thermocouple automatically shuts off the gas valve in the furnace. That's why your thermocouple must be in good condition. If it failed, then replace it with new thermocouple replacement parts.

What distinguishes a thermocouple from a flame sensor?

• Thermocouples are commonly found in older furnaces. However, new installations are now mandated to use electronic fuel injection furnaces. 
• Flame sensors use electronic integrations instead of standing pilot lights, and thermocouples use standing pilot lights.
• Flame sensors ignite only when needed.
• Metal probes and brackets are used in both thermocouple & flame sensors. 

What indications point to a failing thermocouple?

• Contamination marks on the tube, such as discoloration, breaks, or pinholes.
• Bare wire or absent insulation are two examples of wiring wear or corrosion signs.
• Connector damage caused by physical trauma may compromise the accuracy of the test result.

What happens when my furnace thermocouple becomes dirty?

A dirty thermocouple cannot accurately measure the loss of heat. Even while the pilot light is on, a broken thermocouple can cut off the gas supply to the furnace by giving false readings.

How to replace a thermocouple?

So, It's crucial to understand how to maintain a thermocouple's cleanliness and functionality. Read the below process and clean your furnace thermocouple at home.

• Remove the furnace's power connections.
• Using a screwdriver, remove the thermocouple from the pilot assembly.
• Be careful when handling the thermocouple.
• To gently remove the soot, use a strip of steel wool.
• Do not use any cleaning agents, especially none that contain compounds that can catch fire.
• To clean around between the threads of the screw holding the thermocouple in place, use a pencil eraser.
• Reattach the thermocouple to the pilot assembly after it has been cleaned.
• Start the furnace and ignite the pilot light as directed in the owner's manual.

Things to do before starting thermocouple replacement:

• Check the specifications of the old thermocouple.
• Match your new thermocouple specifications with the old one. 
• Install the same specification thermocouple.
• Or, see the requirements of your furnace in the furnace manufacturer manual. 
• 30-millivolts (mV) rating for standing-pilot is a Universal thermocouple. 
• Open-end wrenches, a new thermocouple, and a nut driver are needed to replace the thermocouple.

Steps to replace the thermocouple in a gas furnace:

• Switch off the power source from your furnace unit.
• Unlock the upper access panel.
• Get rid of the old thermocouple.
• Put in a new thermocouple. 
• Connect it to the gas supply and all wire connections.
• Turn on the electricity.
• Verify the proper operation of your furnace.
• Switch off the furnace if a problem arises and dial an HVAC professional. 

Frequently asked questions related to the furnace thermocouple:

What is the voltage range for the thermocouple?

The type of thermocouple determines a thermocouple's output. 

• Types R, S, and B thermocouples are classified as "Noble Metal" thermocouples, 
• Types J, K, T, E, and N thermocouples are defined as "Base Metal" thermocouples,
• Type C and type D thermocouples are classified as "Refractory Metal" thermocouples.
• ANSI/ASTM E230 and IEC 60584 are two types of output vs. temperature characteristics for each type. 
• Read the below information to know the typical thermocouple output of each kind at 250C.

What is the cost of replacing a furnace thermocouple?

Furnace thermocouple replacement costs between $150 to $250, including a new thermocouple cost.

How long does the furnace thermocouple last?

Thermocouple efficiently runs for 10 to 15 years. If your installation and maintenance are correct, it will run up to 20 years.

Can I replace the furnace thermocouple myself?

If you know about HVAC parts replacement, you can easily replace thermocouples. It takes less than two hours.
                                                                                               

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