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How to Tell If A Thermocouple Is Bad [5-Step Guide]

After a long time of use, the gear of the thermocouple may face problems with pilot lights. I know it’s really hard to tell if it has started to malfunction or not. 

How to know if a thermocouple is bad?

Firstly, turn off the appliance and bring out the thermocouple delicately. Then attach a voltmeter between the thermocouple and the gas valve. After that, generate heat on the thermocouple. Lastly, observe the reading of the voltage meter.

I understand this seems quite confusing for you. So, I have prepared a broad discussion to find out the actual reason. 

If you’ve got a few minutes to spare, stay with me!

Ensure The Position And Sanctity of Thermocouple

A thermocouple is a sensor that calculates the temperature. It is being used in a broad range of applications. This device is manufactured in a variety of styles, models, and technical specifications.  

Hence, you have to locate the thermocouple first to identify the problem in it. Most of the gears set the thermocouple with a spring lamp. 

The device can get dislocated while cleaning or other maintenance. It can result in overrunning your central heating pump.

Sometimes the sporadic movement of the thermocouple can also shake its position. The proper place for the device is in the flame of the pilot light.

How to Know If a Thermocouple Is Bad?

To operate correctly, a thermocouple requires the full heat from the pilot light. So that it can produce an ample amount of electrical flow. Yet, there are multiple causes behind the workflow being hampered. 

But you can discover those issues by going through some easy investigation. Here I’ve shown a 5-step method to find out if your thermocouple is bad or not.

Sounds interesting? Then let’s get your work done!

Step 1: Switch off The Gear

Before starting the job you must turn off the appliance. Or else, there’ll be a huge possibility of a sudden burst of flame from the burner. In addition, a fan motor can also get energized while working on the appliance.

Who wants to get burnt or experience a shock?

Absolutely you don’t want that. Thus, find out the control of the gas valve and switch it off immediately. It will secure your own safety.

Step 2: Bring out The Thermocouple from The Gas Valve

The next step is to remove the thermocouple from the gas valve. Generally, thermocouples have no wire connections. 

Mostly, they are connected through a thin copper tube.

First, lose the connection of that copper tube. Then delicately drag out the thermocouple. And put off the thermocouple connector from the gas valve.

Step 3: Attach A Voltmeter

To examine the gear, you’ll need a voltmeter. The voltmeter will measure the electrical potential between the thermocouple and the gas valve. This instrument contains two probes; red and black.

To help you, I am leaving a list of the most effective voltmeters-

Product 1
Product 2

While buying the voltmeter, try to get one with the clamps. Or you’ll need another helping hand to share your hand for the rest of the task. 

Anyways, connect the red string to the thermocouple. Then attach the black clamp to the gas valve. Experts suggest counting the voltage (v) in millivolts. 

Step 4: Generate Heat On The Gear

In this task, you’ll need to heat the thermocouple. For that, turn on the gas valve and put it in the ‘Light Pilot’ setting. I’ve seen quite a few appliances require turning and holding the valve to control. 

Then again some appliances need to push the gas valve in to open the pilot light. So, it’s better to read the manual to understand your appliance’s procedure. Or you might catch an electrical fire on your appliance.

Finally, we will count the voltage level in the upcoming segment. Sounds exciting right?

Read through the next step!

Step 5: Read The Voltage Level

Reading the voltage level is the last step to find out the real cause. First, light the pilot light and keep observing the voltage meter. Wait until your thermocouple properly generates heat. 

The desired voltage should be around 30 to 40 millivolts. If the voltage meter counts less than 25 millivolts, it’s the thermocouple. In that case, you have to replace a new thermocouple.

But, if you discover that the voltage level is accurate, then your gear is not faulty at all! 

What If The Problem Is Somewhere Else?

If the thermocouple isn’t bad, then what’s creating a problem? I know this is the first question that hits your mind.

Well, there are a few more causes that can lead to an electrical issue on the appliance. It can be a pressing problem in your gas-fired heater. 

An aged heater can create issues with gas valves, control panels, or even burners. A damaged heater can turn on the gas oven automatically.

Sometimes you’ll notice tour appliances aren’t lighting or lighting sporadically. It’s because of the dirt build-up inside the igniter. 

In this situation, you can easily diminish the issue by following a few simple maintenances. 


Question: Can I clean my thermocouple?

Answer: Definitely, you can! Though you have cleaned the device with a soft hand.  Use any type of steel wool or emery cloth to wipe off any dirt. But cleaning the device won’t fix any technical issues.

Question: How do you bypass a thermocouple?

Answer: Unscrew the tilts switch wire. Use an 8mm wrench to pull off the thermocouple. Take off the valve housing aside through a 133mm socket wrench. Now, remove the valve using pliers. Finally, put back the thermocouple inside the box.

Question: Should thermocouples be in pilot flame?

Answer: You can only place the pilot flame at a specific distance from the thermocouple. When the flame is weak, boost up the flame to reach the device. Then again, a way too strong flame is also inaccurate. 

Final Notes

Let’s be apart from here. I’ve explained everything regarding how to tell if a thermocouple is bad. Hopefully, you have understood how to find out the issue.

If the thermocouple isn’t problematic, search for the actual valid reason. Such as the gas heater, auto ignitor, and pilot light. Meanwhile, don’t forget to maintain safety measures.

Until next time, take care!