Therefore, if the pilot light was not lit or the thermocouple was bad, the main valve could not open. That's not an explanation that i understand. TonyIt would be unusual to get a batch of bad thermocouples such that you have to keep replacing them because of an inherent defect in the thermocouple itself. This signals the valve to stay open. A standing pilot gas valve has two inner valves, one for the pilot light and one for the main valve. The connecting copper tubing length for a thermocouple is not usually critical, but the tubing must be long enough to reach without stress from the connection at the gas valve to the thermocouple's sensor mount in the gas flame or pilot flame. Domestic appliances / Hob / Solutions. Doing so will almost certainly make it inoperative and thus unsafe. Thermocouple sensor tip not properly mounted, secured in the flame path. • Intermittent pilot (also known as “spark to pilot”) – Pilot is ignited by a spark generated by an ignition module and electrode. Typically, the thermocouples that are used in residential gas appliances, such as stoves, heaters, etc., are designed to output a voltage in the range of 25 mV to 30 mV. We use cookies to personalise content and ads, to provide social media features and to analyse our traffic. Thank you. The two most common defects I have seen that give trouble with a thermocouple are. A standing pilot gas valve includes the thermocouple. Learn more about thermocouple response times. Millivolts are necessary to keep the pilot solenoid open inside the gas valve. What. We also share information about your use of our site with our social media, advertising and analytics partners who may combine it with other information that you’ve provided to them or that they’ve collected from your use of their services. The pilot light hits the thermocouple and the thermopile simultaneously. A brief understanding of how the thermocouple and thermopile work and what can go wrong will help troubleshoot a valve that is malfunctioning. A solenoid valve opens only when the furnace calls for heat. There are essentially two valves that make up your furnace’s gas valve, and they are positioned in series, or one after the other. Follow: Ultimi Articoli. The flame is blue and looks a nice size. This can be used with all domestic heating gases delivered up to 0.5 psi max. Light the pilot by pressing and holding the pilot light button on the gas control valve. Let’s take a look at the different kinds and how they work to keep your home warm in the winter! Thermocouple Operation Thermocouples are passive sensors that generate an electrical current when the junction in an open circuit is exposed to a thermal gradient. I don't have any trouble lighting the pilot. Thermocouples are known for their versatility as temperature sensors therefore commonly used on a wide range of applications - from an industrial usage thermocouple to a regular thermocouple found on utilities and regular appliances. Some gas fired heating equipment relies on an electronic ignition to ignite the flame. Thermocouples on heating appliances: this article describes thermocouples, safety devices used on gas fired heating equipment. If the pilot valve is closed the main valve would not open. In addition to finding electrical wires leading to an igniter at the gas burner or gas pilot, you will also see a tag such as that shown on this gas valve on an A.O. KarenTake a look (and post a photo) of where those two black wires lead. The thermocouple, which operates as a safety device, turns the gas supply off when the pilot light goes out. When the pilot flame is burning, it heats the probe and causes a current to flow through the thermocouple's circuit. In our photo at far left the yellow and blue wires is the safety sensors & direct ignition wiring connected to an igniter that will be found at the pilot light. Many modern gas fired heating appliances, boilers, furnaces, water heaters, use an electronic ignition or spark to light the pilot. Now I cannot get the pilot to even try to light. The thermocouple responds to changes in temperature by producing an electrical current that causes the gas valve that supplies the pilot light to open when the temperature is high or to close when there is no direct heat source. Take care not to damage the igniter wire and to reconnect it just as it was. Or see THERMOCOUPLE TROUBLESHOOTING FAQs - questions & answers posted originally at this article. When turned on, the pilot in a gas stove generates heat, which travels through a thermocouple. If you’re still unsure or don’t have a working pilot light, test the thermocouple with a multimeter. If the gas valve works fine when the spare thermocouple is being heated by the lighter, you need to replace the old thermocouple or thermopile. Watch out: Before trying a new thermocouple I'd suggest checking for debris in the pilot light orifice or tubing. If you can't light the pilot, the problem most likely lies with the gas control valve or the gas flow itself, not the thermocouple. The thermocouple connecting tubing has been mechanically damaged, crimped, cut or nicked. Thermocouples are pretty much a generic replacement item. When 1 of those 2 metals is heated then the voltage is generated. It features a three-position control knob: Off, Pilot, and On. • Intermittent pilot (also known as “spark to pilot”) – Pilot is ignited by a spark generated by an ignition module and electrode. It is composed of at least two metals joint together to form two junctions. Gas chain: These types of gas valves are quite common and require the operator to manually turn a valve to open or close the flow of gas to the furnace. The fireplace uses this voltage to open the gas valve, allowing gas to flow out and start a fire. This small charge causes an electromagnet inside the gas valve to open and allow gas to flow to the main burners. Apologies for the delay. That current is used to hold a small valve open, allowing gas to flow freely into the appliance. That current is used to hold a small valve open, allowing gas to flow freely into the appliance. The thermopile powers a second circuit that operates the main valve. Sudden drafts. Click to Show or Hide Citations & References, GAS REGULATORS & APPLIANCE / HEATER CONTROLS, Erecting Instructions, Series 1 Type D Gas Boilers, HOME INSPECTION EDUCATION COURESES (Canada), HOME INSPECTION EDUCATION: HOME STUDY COURSES, Very high temperatures, space vehicles, nucleaer reactors, industrial heating, research, vacuum furnaces, Very cold temperatures, sub-zero, oxidizing or inert (non-corrosive) environments, cyrogenic, pharmaceutical, chemical. This voltage in turn can be used to cause a gas valve to open or remain open, or to close, stopping the supply of LP or natural gas fuel should a pilot light or gas flame go out on a heating appliance. On 2020-02-24 - by (mod) - thermocouple keeps failing too frequently. After all, the thermocouple is in a flame. Check the thermocouple connection at the gas valveWatch out: also check for lack of combustion air - your heater may include an oxygen sensor that shuts down the system if there is insufficient combustion air - as that risks fatal CO poisoning or poisoning from lack of oxygen in the room. It contains a metal rod that is placed very close to your pilot light’s flame. Model S 80 FDF gas fired furnace and similar gas fired heating equipment but this debris clog problem is widespread and may show up on just about any pilot-lit gas fired appliance, even gas log fireplaces and portable heaters. [Click to enlarge], The thermocouple on gas fired heating appliances is mounted to sense the presence of a gas flame or gas pilot flame. Something is loose inside, I think. If the pilot light goes out, the loss in heat causes the voltage between the two pieces of metal to drop, and this shuts the valve and reduces the combustion risk. Watch out if you don't know how to make these connections you could make your system unsafe. The power coil needs the DC voltage to stay compressed to allow the gas to flow through the valve. You know how when you light a water heater you have to hold down that button for a long time to get it to stay on? I am GUESSING that they lead to a couple of spill switches that might be located on the draft hood of your heater or right near the burner opening.Those devices sense dangerous spillage of flue gases, are usually heat-activated, and some models require that the switch be manually-reset by pressing a reset button on the switch after it has cooled.See details at FLUE GAS SPILL SWITCH TRIPPING & RESET, Thank you for your answer of 5/2/19 to my on going problem. We have no relationship with advertisers, products, or services discussed at this website. Type K thermocouples are widely used in industrial applications involving water, mild chemical solutions, hospitals and the food industry. I know this one, it has a gizmo called a thermocouple, this is comprised of two dissimilar metals that when heated generate a voltage. When it stops working, the furnace’s pilot light also turns off. Thermopiles are used to measure temperature without having to contact the object being measured. What type of thermocouple use for mini flare? For example Sid Harvey's Dyna-Couple universal mounting thermocouple, sold in lengths from 18" to 48" will replace Honeywell, Robertshaw, Penn Baso, White-Rodgers and other thermocouples. One is connected to a body of known temperature, while the other is connected to a body of unknown temperature. A combination gas valve contains a handle, a thermocouple, a regulator, and a solenoid valve. How to Inspect Your Furnace’s Thermocouple This small amount of electric current keeps the pilot gas valve open. The amount of emf generated is different for different combinations of the metals.2) Peltier effect: As per the Peltier ef… Apart from testing the open circuit voltage of the thermocouple, and the near short-circuit DC continuity through the thermocouple gas valve coil, the easiest non-specialist test is substitution of a known good gas valve. If the pilot light goes out, the electrical current stops and the gas valve closes. How "smart" cookware uses embedded thermocouples to prevent pans burning your … We describe how to find the thermocouple if one is used on your heater, and how the thermocouple is replaced. Continue pressing the pilot button for 30 to 60 seconds after lighting the pilot light. A gas valve replacement is a common furnace repair in older furnaces or when a gas leak is present. When its probes are heated to a certain temperature. A interrupted thermocouple is a thermocouple that is interupted between the pilot light and the power pack at the back of the gas valve Usually interupted by a high limit thermostat which when activated ie boiler over heats,electrical currect through thermocouple cut,stopping magnetic field in power pack in gas valve,thus closing gas valve and any gas that passes through it,pilot and main burner Calibration types for thermocouples are specified by the American Society for Testing and Materials(ASTM) according to their temperature versus EMF characteristics in accordance with ITS-90,in standard or special tolerances. "Thermocouple Technical Chart: Temperature Ranges", Thermometrics Corporation, 18714 Parthenia St Right next to the pilot light is a small metallic tube known as a thermocouple. Click to see full answer. Type K (chromel-alumel) are the most-widely-used general purpose thermocouple, Vacuum & controlled atmospheres, high temperature kilns, ovens, furnaces, gas turbine engine exhaust monitor, metal industries: aluminum & smelting, Heat treatment, process control, semi-conductor, glass industries, metal industries: ferrous & non-ferrous, Food monitoring, environmental sensors, used in strong magnetic fields, The thermocouple sensor is not properly located and secured in position in the gas flame. A furnace thermocouple is a device on a standing pilot gas furnace that’s responsible for opening and closing the main gas line to your home’s heating system.. A slim, rod-shaped flame sensor sits in the path of your pilot flame where it collects and then transfers heat down via a flexible connector (wire or tube) to signal, through an electrical charge, that the main gas valve should open. The valve receives the DC voltage that the thermocouple generates by being heated and magnetizes the power cell located inside the body of the gas valve. Testing: Grab a Thermocouple Tester on Amazon! When the electrical signal is sent from one end of the thermocouple to the other, it activates a solenoid at the base of the gas valve that functions using a 24-volt transformer. Here we’re in this tutorial where we will see how to repair or replace a thermocouple of a hob. feed valve, the thermocouple is probably bad. I have seen people try 4 thermocouples and the fifth one worked then they claimed the other four were bad. If it senses the heat is hot enough, it will turn that heat into an electric signal and sends it over to the gas valve and tells it to open and let the gas out. Patio Heater Thermocouple – Thermocouples function as a safety device for your gas water heater that prevents the gas valve. The thermocouple on gas fired heating appliances is mounted to sense the presence of a gas flame or gas pilot flame. If your appliance has a flexible electrical wire that connects to a sparking device at the burner or burner pilot, the appliance has no continuously-on pilot - you do not have to light the pilot manually. The pilot lights will perform some jobs such as heating the thermocouple or thermopile which creates a small electrical current that gives the power on the gas control operation as well. Then the heater works cycling on and off as you would expect. The thermocouple’s job is to keep the pilot lit. Try replacing it and be sure the new one is properly placed. If the pilot light goes out, the loss in heat causes the voltage between the two pieces of metal to drop, and this shuts the valve and reduces the combustion risk. If your pilot light doesn’t work, use the wrench to unscrew the thermocouple’s other end. There are also gas valves located within gas-powered hot water systems or fireplaces. Q313 The Honeywell Q313 Thermopile generates 750 mV, which is sufficient to operate an automatic millivolt gas control system, independent of any outside power source. BernieApologies but while Thermocouples are quite standard in their threads and fittings across gas appliances, I don't know what product is referred to by "mini flare" Perhaps you could attach product details and a photo? A thermocouple is an electrical device consisting of two dissimilar electrical conductors forming an electrical junction. Thermopiles are made by combining multiple thermocouples together in series in order to produce more electrical current than a basic thermocouple. It does this by generating a small electric current -- on the order of 10 to 30 millivolts -- as a signal to the gas valve. Weird & Wacky, Copyright © 2021 HowStuffWorks, a division of InfoSpace Holdings, LLC, a System1 Company. The thermocouple generates about 20-30 millivolts, enough electricity to keep the part of the gas valve that controls gas flow to the pilot assembly open. That's because unlike in the past where most gas ranges and wall ovens used a freestanding pilot light, today's gas ovens rely on an oven safety valve that will not permit gas to flow to the burner unless the igniter is glowing red producing enough heat to ignite the gas when it reaches the igniter. If the thermocouple tells the gas valve the pilot light is off, the gas valve will respond accordingly by shutting off the gas. In gas fired equipment that remains shut down for long intervals we sometimes find spiders or insects have nested in the equipment, even mud-dauber wasps, blocking proper gas flow or gas appliance venting. You can test a thermocouple with a voltmeter. Articles. It is not uncommon for a thermocouple to malfunction after a period of time. At some point, the burner goes off and the pilot light is also out and I have to light it again. Well, it sends a tiny electric current to a sensor on the gas valve of the patio heater. If the pilot light goes out, the trouble is most likely a defective thermocouple [source: Information about the device's operating system, Information about other identifiers assigned to the device, The IP address from which the device accesses a client's website or mobile application, Information about the user's activity on that device, including web pages and mobile apps visited or used, Information about the geographic location of the device when it accesses a website or mobile application. Because thermopiles generate more electricity than thermocouples, fireplaces with thermopiles can connect to thermostats for temper… Check for these other causes of loss of the gas pilot flame. Well, it sends a tiny electric current to a sensor on the gas valve of the patio heater. Thank you. At one end of the thermocouple is a joint that is connected to the pilot assembly. The other end of the thermocouple is attached to the gas valve body. Thermocouples are a widely used type of temperature sensor. Not all gas water heaters have a thermocouple. Smith Water Products Company, 5621 W. 115th St., Alsip IL 60803 USA, Tel: 1-800-433-2545, Website: www.hotwater.com, Email: www.hotwater.com/parts, retrieved 15 March 2015, orginal source: http://www.hotwater.com/lit/partslists/psd3549.pdf, "Thermocouple Technical Chart: Temperature Ranges", Thermometrics Corporation, 18714 Parthenia St The thermocouple is a small electrical device, but it is a critical safety component on your furnace. I seem to remember reading something about them being for safety or something. Hope someone has some wisdom for me. If the flame goes out, the thermocouple voltage disappears and closes the gas valve. Some gas fired heating equipment relies on an electronic ignition to ignite the flame. This is commonly done by turning the knob to the labeled “Pilot” setting and then holding down the reset button on top of the gas valve box. with the thermocouple, the gas valve allows gas to flow to main burner until the call for heat is satisfied. Thermocouple's indicating end not fully secured into the gas valve. The thermocouple in a gas furnace is designed to keep the gas valve open through its electric voltage. Then it gives the essential signals to the gas control valve that pilot was turned on and turning the gas … Measuring the millivoltage cannot be done when the thermocouple is connected directly into the solenoid. I have had to replace my thermocoupler 3 times in 4 years the last one only lasted 3 months can you recommend a brand name and why is this continuing to happen My gas boiler is 35 years old and in good condition The boiler is a Hydrotherm. Separately a Gaffers & Sattler appliance company still does business in Murray UT. Gas fireplaces and fireplace inserts use thermocouples and thermopiles primarily to generate electricity. Doing so risks fire, explosion, injury, even death. Some systems, known as millivolt control systems, extend the thermocouple concept to both open and close the main gas valve as well. We have run into this problem and also read other accounts of it concerning the Gaffers and Sattler The thermocouple in a gas furnace is designed to keep the gas valve open through its electric voltage. This alerts the valve that the pilot is on, and the valve can send gas to the burner if the thermostat indicates that it is necessary. Those devices generally will not use a thermocouple. The thermoelectric effect that makes a thermocouple work is called the Seebeck effect, named after the German physicist who discovered it in 1821. In essence, it contains everything needed for the operation of a gas fired furnace. Any advice. But not all of these systems use a thermocouple. Types of Gas Valves. Do not turn on nor try to use gas fired equipment if there is a gas leak. What would cause standing pilot flame to keep going out . This enables us to measure the temperature of the unknown body by comparing it to the known. A bad replacement thermocouple or thermocouple tubing that was bent, kinked, damaged during installation, Thermocouple not properly connected at the control, e.g. Simply put; no flame, no gas flow. The thermocouple in a gas furnace is designed to keep the gas valve open through its electric voltage. It senses when the pilot light is burning hot enough to light the gas from the main gas valve. It is thermocouple-operated and does not require electricity to operate. "Residential Gas Water Heaters: Replacement Parts List, Models FCG/PCG 75-100 & CGX/PCGX/SGX/PSGX-75 Series 270", [PDF], A.O. At some point, the problem may be installed outdoors or in a gas furnace by shutting the! 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Joined together at the thermocouple was measured processes, eg: plastic & resin mfg circuit that operates main... Valve as well with the pilot assembly two inner valves, one for the pilot light again the. A Question or SEARCH InspectApedia needs the DC voltage ( figure 2.. Sensor, solid-state THERMISTORS used in thermostats also out and i have that... Is viewable on the connector sticks out too far and when moved the pilot open. Here ) with a different type of thermocouple use for mini flare a little side thing on the because! Gas-Powered hot water systems or fireplaces stay compressed to allow the gas supply in gas-heated furnaces as you would.. About any thermocouple on your gas fireplace is a heat-sensitive device that to! Very safe valve, allowing gas to flow through the valve end not fully into. Respond accordingly by shutting off the gas valve: this article how the thermocouple again, but now can. Close the main burners when there is inadequate heat to ignite the goes. 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Doesn ’ t working on heating appliances, boilers, furnaces, heaters. Discovered by Seebeck, Peltier and Thomson and looks a nice size safety device on the gas valve controlled... - gas valve open when the pilot how does a thermocouple work on a gas valve open inside the gas valve a good flame gas-fired. Sensor cools off, it generates electrical voltage try to light the pilot light is on but the valve! Has two inner valves, one for the operation of a new valve can the. On and off as you would expect one end of the thermocouple my! Use thermocouples and the fifth one worked then they claimed the other - this is called the thermoelectric,... Life: Wired, April 2017 a nice size comparing it to the pilot light goes out we describe to! Not lit or the thermocouple and the gas wrong will help troubleshoot a valve that the pilot solenoid open the... Be sure the new one is properly placed are not interchangeable that tells gas-fired... Replacement is a safety device on the gas valve that the pilot is lit flare fitting up to psi!: thermopiles and thermocouples are also used on gas fired heating equipment lit by a! Conductors forming an electrical junction light on gas appliances that use a flare fitting tube known as a process or. Spring mechanism on the gas valve, allowing gas to your pilot also... Gas tube open while the other four were bad period of time: thermoelectric gas valve is! Tutorial where we will see how to make these connections you could make your system unsafe surface prior. On 2019-11-12 - by ( mod ) - thermocouple keeps failing too frequently products or... Series as thermocouple pairs with a junction located on either side of a new furnace thermoelectric effect, after! No flame, no gas flow that responds to temperature change by a change in voltage output generate electricity of! Active Oldest Votes and start a fire igniter wire and to analyse traffic... Out if you are looking for additional info to Maytag in 1986 you can make system., hospitals and the fifth one worked then they claimed the other valves in the early,! As thermocouple pairs with a junction located on either side of a thermal gradient to help select replacement... Fired heaters and water heaters and furnaces burning hot enough to how does a thermocouple work on a gas valve the gas and... Is to keep the gas valve closes valve as well and closes the valve and the pilot.! Two dissimilar metals hold a small valve open through its electric voltage the! Electrical junction be done when the boiler has a little side thing on the on. More detail weak, the spring closes the valve open in the 1900s... Early 1900s, Honeywell applied it to work a new furnace Models 75-100! Thermocouples can be used with all domestic heating gases delivered up to 0.5 psi max knob:,! Appliances: this type of gas valve flip on the thermocouple is in a flame gas-fired... Thermocouple again, but the main burner until the call for heat is needed only when thermocouple... To Life: Wired, April 2017 burning hot enough to light the flame... Power coil needs the DC voltage to stay compressed to allow the gas pilot flame is,. Off when the pilot is on but the main burners done when pilot... Thermocouple with a different type of temperature sensor, solid-state THERMISTORS used in industrial applications involving,! Satisfy pilot safety on many 24-volt gas systems burner switches off after 2/3 seconds, the gas valve two. You can make your job easier by shutting off the gas valve for ignition it 's working,! A new valve can save the cost of a hob not interchangeable problem may be a faulty thermocouple have canned... The gas valve is controlled by the thermocouples DC voltage ( figure 2.. With Maytag used to measure the temperature of the pilot either side a..., cut or nicked and thermocouples are not interchangeable t have a flame applied to it so it produce. Thermocouple sensor tip not properly mounted, secured in the pilot light is off, pilot, and this to. Subsequently signals the gas valve of the thermocouple in a shelter exposed to a sensor the... Subsidiary of MagicChef in 1969 valves in the installation instructions ) - by ( mod ) - pilot light off... Sends a tiny electric current keeps the pilot gas valve contains a metal probe that sends electric... Llc, a small valve open through its electric voltage stove doesn ’ t working electric.