Hopefully, you have understood how to find out the issue. When these two metals are heated, they produce a measurable electrical current. To gain access to the pilot burner, pull the door out of the furnace housing. This is what a cheap K-type thermocouple looks like: Note that the wires to the thermocouple (the little metal ball at the end of the cable there in the upper left corner of the picture) are bare - they can easily be shorted by bending or twisting the wires. After a minute, check the thermocouple with the multimeter if its less than 25 millivolts, you need to replace it. If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. When purchasing a new thermocouple, be sure to check the specifications to make sure it is the correct size and type. Never work on a gas appliance, especially around the burners, igniters, or pilot lights with the gas turned on. When it stops working, the furnaces pilot light also turns off. Then attach the other lead to the end of the thermocouple by the igniter. Get free, zero-commitment quotes from pro contractors near you. Pilot lights must be near the main burner to ignite the gas on the burner when the appliance comes on. Finally, its important to properly maintain your thermocouple to ensure it works correctly for a long time. A second set of hands is helpful for this step to keep the pilot burning. Take the two leads from the meter and touch themthe meter should read zero. When the thermocouple is dirty, it won't produce enough voltage to open the gas valve, this will cause the pilot light to go out after you release the bypass button. How to know if a thermocouple is bad? It can be a pressing problem in your gas-fired heater. By creating an account you agree to the Hunker, How to Change a Thermocouple on a Fireplace, How to Troubleshoot an Electronic Ignition for a Superior Gas Fireplace, Adjusting the Gas-to-Air Ratio on a Heat-N-Glow Fireplace. How Does a Gas Water Heater Thermocouple Work? Use any type of steel wool or emery cloth to wipe off any dirt. An old toothbrush is a perfect tool for this job. If the thermocouple is malfunctioning, the most likely culprit is a loose connection. If you suspect a bad thermocouple, diagnosing the problem may not be all that difficult. A burned out or broken thermocouple should be replaced. Answer: Unscrew the tilts switch wire. Some thermocouples will look slightly different, so check your furnace manual. Connect the thermocouple to the pilot burner assembly bracket Connect the gas line and the gas valve to the pilot thermocouple Screw all the nuts tightly on the gas valve Now turn on the power of the furnace. Use a lighter or torch to hold a flame under this end. Fortunately, repairing a thermocouple is a relatively simple process that requires minimal tools and a bit of patience. If all heater zones show continuity then check the resistance of each zone and compare it to the value shown on your hot-runner. After that, generate heat on the thermocouple. Carefully remove the thermocouple from the gas valve by loosening the copper connector. If you hear the clicking sound but cant see the arc or the burner doesnt light, you may have a bad igniter. Ive seen quite a few appliances require turning and holding the valve to control. In this task, youll need to heat the thermocouple. If the voltage meter counts less than 25 millivolts, its the thermocouple. If the thermocouple isnt problematic, search for the actual valid reason. If the flame lights and goes out when you release the gas control knob after holding it in for the recommended 20 to 30 seconds, that's the sign of a thermocouple malfunction. Put Everything Back Into Its Place 07. Make sure that the wiring is protected with insulation and is not damaged or broken anywhere in the circuit. By subjecting a suspect inhomogeneous thermocouple to another set of temperature gradients for testing, can result in a different temperature output which will not help in its specific area of use. This procedure is a bit more involved and requires a voltage meter. Video of the Day. Hunker may earn compensation through affiliate links in this story. If it is mashed or one of the wires is broken off right at the thermocouple then youre going to have get a new one - that kind of thing cant be fixed. It may have gotten crushed or one of the wires may have broken off. But cleaning the device wont fix any technical issues. Now, remove the valve using pliers. If a thermocouple tests at 25 millivolts or lower, it doesnt have the power to keep a pilot lit and it should be replaced. After a long time of use, the gear of the thermocouple may face problems with pilot lights. They will replace the thermocouple when they do this. On some gas cookstoves, the igniter may be inside the sealed burner assembly. Make sure the connection is clean and dry. The pilot should heat the top 7/8" of the thermocouple with a clean (blue) flame. If the control is accurate and slowly drifting to inaccuracy, it could mean the thermocouple is of bad quality. If your appliance wont light or only lights sporadically, the most common problem is build-up on the igniter. Remember that you are working around open flames. 2. If the resistance measurement shows an open circuit, look closely at the thermocouple itself. Many new appliances have auto-igniters that take the place of the pilot light. References. With over 12 years of experience, Gevorg specializes in residential and commercial appliance repairs as well as heating, ventilation, and air conditioning (HVAC) services. Answer: You can only place the pilot flame at a specific distance from the thermocouple. Use a can of compressed air to gently blow away any dust and dirt from the thermocouple. Pilot hood and flame direction. If the thermocouple is working, you should be able to measure 30 to 40 millivolts of voltage at the connection end of the tube when the pilot flame is on. Check the thermocouple for the correct depth of immersion. Ive explained everything regarding how to tell if a thermocouple is bad. Many times the readings are not correct or work at all, due to interference from crimp on connectors, solder, wire insulation, or incorrect materials being used for the connections. If the thermocouple is still not working correctly, you may need to replace it. Next, attach the leads from the multi-meter to the thermocouple: put one on the side of the thermocouple, and attach the other lead at the end of the thermocouple that sits in the pilot light. Anyways, connect the red string to the thermocouple. Remember to be safe when doing repairs around your home. Auto-igniters are quite simple. Did you know you can get expert answers for this article? So, I have prepared a broad discussion to find out the actual reason. Start the test by unscrewing the thermocouple from the gas valve. If the reading is less than 25 millimeters, it should be replaced. Looking at the pilot light and the thermocouple, most of the thermocouple should be in the flame of the pilot light. Five time constants are required for the sensor to approach 100% of the step change value. Expires 04/30/23 *Available with approved credit. Replace the furnace access cover and test the furnace operation by changing the thermostat settings to make sure the furnace turns on and off properly. If you suspect that you have a defective thermocouple, the best way to evaluate a used thermocouple is to place a new, or known good thermocouple adjacent to the suspect one in order to compare and document readings between both. Turn the pilot light on for at least 30 seconds and the release it to see if goes out; if it does, its a sign your thermocouple isnt working correctly. Your furnace pilot light should burn just fine if you have got all these steps right. You will need a wrench, multi-meter, and a flame source, like a candle or a lighter, to perform the test. After that, generate heat on the thermocouple. Gevorg Grigorian. Call for details. Mine showed pretty much zero ohms from pin to pin, so at least it wasnt an open circuit. It's also a good idea to pull the pilot tube completely out and poke a needle in the flame orifice. A few steps are involved in this test but shouldnt be a problem for most homeowners. Now that is working again, it shows about 15 ohms. And put off the thermocouple connector from the gas valve. Make sure that the wiring is protected with insulation and is not damaged or broken anywhere in the circuit. Just the fact that you have to shut down and replace a thermocouple means lost revenue. By signing up you are agreeing to receive emails according to our privacy policy. Wait until your thermocouple properly generates heat. Well, there are a few more causes that can lead to an electrical issue on the appliance. As a small thank you, wed like to offer you a $30 gift card (valid at GoNift.com). Required fields are marked *. Your igniter may or may not have a pilot hole. Following a few steps and applying a bit of knowledge can have the fire back on in your gas appliance in no time. Firstly, turn off the appliance and bring out the thermocouple delicately. Do You Need Emergency Furnace Repair? Separate the thermocouple connector from the gas valve. There may be a broken wire in the plug if you find an open circuit from pin to pin. Lets be apart from here. For a basic test, attempt to turn on the pilot light again. Save my name, email, and website in this browser for the next time I comment. Sometimes the problem is simply that the thermocouple probe is too far from the flame. Thermocouples are essential components in many heating, cooling, and combustion systems. Yes, you can clean a thermocouple, but the task must be done with a light touch. That was odd. How to Survive an Encounter with an Ostrich, Unlock expert answers by supporting wikiHow, https://www.familyhandyman.com/plumbing/water-heater/how-to-fix-a-water-heater-pilot-light/view-all/, https://www.bobvila.com/articles/furnace-troubleshooting-2/, https://www.familyhandyman.com/heating-cooling/furnace-repair/do-it-yourself-furnace-maintenance-will-save-a-repair-bill/view-all/, https://www.familyhandyman.com/plumbing/valves/how-to-locate-your-gas-shutoff-valve-and-water-shutoff-valve/view-all/, https://www.familyhandyman.com/plumbing/water-heater/how-to-replace-a-water-heater-thermocouple/view-all/, https://www.sensorsmag.com/components/using-precision-digital-multimeters-for-quick-checks-temperature-transducers, https://highperformancehvac.com/how-test-thermocouple-multi-meter/, https://heatinghelp.com/systems-help-center/thermocouple-testing-procedure/. Is still not working correctly, you need to replace it be in the circuit zones show continuity then the. 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