Thermocouple placement in flame

Although they are gradually being replaced by electronic ignition devices, pilot lights still provide the flame that ignites many gas appliances, including water heaters, room heaters and stoves.

Pilot lights depend on the electric signal from a thermocouple to stay on, and the thermocouple in turn depends on the heat of the pilot light to provide that signal.

Glitches in this symbiotic relationship are at the bottom of many pilot problems. The thermocouple is a heat-sensitive electronic device that generates a small electrical signal when it reaches a certain temperature. In most appliances, a clip holds it about an inch from the pilot aperture. When you light the pilot and the flame heats the thermocouple probe to its critical temperature, a small electric current signals the gas valve to stay open.

It takes about 20 seconds for the probe to reach this temperature when you light the pilot, so you generally have to hold the valve open manually by pressing a button for this length of time.

Adjusting the pilot often adjusting the thermocouple, which can fail to keep the gas valve open for one of at least three reasons.

How to Determine if a Fireplace Thermocouple Failed

It may be too far from the pilot flame, the flame may be too small or intermittent, or the thermocouple is faulty. Correcting the first condition is a simple process. Simply shut off the gas, reach under the burner and push or pull the probe to reposition it. If the thermocouple is faulty, remove it by unscrewing it from the burner and pulling it out. Reverse the procedure to install a new one. If the pilot flame is too small, you may be able to make it larger by turning the pilot adjustment screw on the valve control counterclockwise with a screwdriver to open it.

If this screw isn't labeled, consult the appliance owner's manual to identify it. The cause of a weak flame may also be an obstruction in the pilot tube. You can often remove such obstructions by turning off the gas, unscrewing the pilot tube from the valve control and blowing compressed air from a can through the tube. You can also poke the aperture of the pilot tube with a needle.

If the pilot on your gas appliance goes out frequently, there may be a draft in the room. Heater gas controls are frequently at floor level, and air can sweep in under nearby doors and blow out the pilot.

One solution is to block the incoming air with a metal screen; another is to install a sweep on the bottom of the door.

Poor pilot performance can also be related to blocked venting that leaves the pilot with insufficient oxygen to keep burning. You may have only to remove debris from the vent opening to restore the pilot. Chris Deziel has a bachelor's degree in physics and a master's degree in humanities. Besides having an abiding interest in popular science, Deziel has been active in the building and home design trades since As a landscape builder, he helped establish two gardening companies.

Skip to main content. Home Guides Home Home Improvement. About the Author Chris Deziel has a bachelor's degree in physics and a master's degree in humanities. Deziel, Chris. How to Adjust a Pilot Light. Home Guides SF Gate. Note: Depending on which text editor you're pasting into, you might have to add the italics to the site name.

Customer Service Newsroom Contacts.The thermocouple on your gas furnace is a heat-sensitive device that transmits a small electrical signal to the gas valve to keep it open when the pilot is on. The thermocouple lasts for 10 years or more, and when it fails, the pilot won't stay lit and the fireplace won't work. Replacing it is a relatively simple job that you can accomplish with a wrench.

Before you replace it, though, it's a good idea to test it with a voltmeter to make sure it's actually malfunctioning. If it checks out, the problem with your fireplace could be a blockage in the pilot tube or a faulty gas valve. All gas appliances with standing pilots, such as furnaces and water heaters, have a thermocouple. It's a cylindrical probe about 4 inches long and a quarter to a half inch in diameter that's attached to a 1- to 2-foot length of copper tubing.

The probe is positioned next to the pilot opening so that its tip is in the flame when the pilot is on. The other end of the tube connects to the gas valve by a threaded connector. The tip of the probe contains a heat-sensitive material that generates a small electric voltage — around 25 millivolts — when it's heated by the pilot flame.

The voltage sends a signal to the gas valve to stay open. Without this signal, the valve closes automatically to prevent the release of unburnt gas. When you light the pilot, you usually have to hold in the gas valve manually for about 10 seconds to give the thermocouple time to heat up. Once it has reached the required temperature, you can release the valve control and the pilot will continue burning.

If you can't get the pilot to stay lit, the chances are good that the thermocouple is faulty, but it's best to check before you replace it. You can perform a simple test with a voltmeter. Set the meter to read millivolts, then hold one probe on the metal copper tube that leads from the gas valve to the pilot orifice and the other probe on the connector that holds the thermocouple tube to the gas valve. Have a helper light the pilot and keep the valve control depressed to heat up the thermocouple probe.

About 10 seconds after the pilot starts, you'll get a reading of 25 millivolts if the thermocouple is working. If you get a smaller reading or none at all, the thermocouple needs to be replaced.

Gas furnace won't stay lit. cleaning the flame rod

The only tool you need to replace a thermocouple is a wrench. Use it to unscrew the connector that holds the thermocouple to the gas valve, then unhook the probe from its clip and pull out the entire thermocouple assembly. Before you do this, be sure to turn off the line valve on the gas supply. Take the thermocouple to the hardware store to purchase a new one.

Many styles are available, so look for one that matches. Once you have the new thermocouple, replace it by snapping the probe back into the clip to hold it at the proper distance from the pilot flame, then screw the other end into the gas valve.

Test it by lighting the pilot and making sure the flame stays lit. If you can't get the flame to stay on, try moving the probe slightly closer to the flame until the flame does stay lit. Chris Deziel is a contractor, builder and general fix-it pro who has been active in the construction trades for 40 years.

He has degrees in science and humanities and years of teaching experience. An avid craftsman and musician, Deziel began writing on home improvement topics in Hunker may earn compensation through affiliate links in this story.

How to Change a Thermocouple on a Fireplace. Share this article. Chris Deziel. Show Comments.InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

This article explains what a thermocouple or thermopile is, how these devices work, where they are installed, and what goes wrong with thermocouples. We describe how to find the thermocouple if one is used on your heater, and how the thermocouple is replaced. A thermocouple works to produce a small electrical voltage output by connecting two dissimilar metals or two wires forming a measurement junction at the sensor tip of the device.

When heated the effect of the two dissimilar metals in contact with one another is the production of an electrical current. 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. Shutting down the gas supply to a heating appliance protects against a gas fire or explosion that could occur if a gas regulator valve remain open without proper ignition of the gas flame.

In general we think that thermocouples are less accurate and less sensitive temperature sensors than thermistors, but these low-cost and reliable temperature sensing devices have been used successfully in heating equipment such as gas fired furnaces, boilers, and water heaters for decades.

Thermocouples are also used on gas logs and in gas fireplaces or similar devices. Our sketch at above left, illustrating a typical use of a thermopile, a type of thermocouple, in use at a gas boiler, is adapted from Weil McLain. Thermocouples are used as safety devices that will shut off equipment by shutting down the LP or natural gas fuel supply on some gas-fired heating equipment such as gas fired furnaces, gas fired heating boilers, and gas fired water heaters.

Typically the thermocouple sensor is mounted right in the flame of the pilot light on gas fired heating equipment. Our photo left shows how you may spot the copper tubing of the thermocouple extending between its sensor at the pilot flame of a gas burning furnace and its connection to the gas control valve. The thermocouple on gas fired heating appliances is mounted to sense the presence of a gas flame or gas pilot flame.

The other end of the thermocouple's tubing connects to a port on the gas regulator or gas valve. But not all of these systems use a thermocouple. Some gas fired heating equipment relies on an electronic ignition to ignite the flame.

Those devices generally will not use a thermocouple. The thermocouple and safety shutoff do double duty, since on burners that use a pilot flame the thermocouple senses the pilot flame and won't permit the gas valve to open if the pilot is not lit. A bad thermocouple itself can prevent a gas furnace or boiler from working - if you can light the flame at the pilot manually but then the flame goes out when you release the manual gas feed valve, the thermocouple is probably bad.

A thermopile looks like a thermocouple, and does a similar job - sensing temperature, such as a gas flame to function as a safety device. Watch out : thermopiles and thermocouples are not interchangeable. When replacing a temperature sensing device like a thermocouple or thermopile, you should be sure to purchase the proper part.

Thermopiles are made by combining multiple thermocouples together in series in order to produce more electrical current than a basic thermocouple. Externally a thermopile still looks like a single sensing device. There we note that millivolt thermopiles are used in lieu of a simpler thermocouple when the device needs to operate a thermostat as well as the gas valve. The manufacturer of the heating appliance in which the thermocouple is used will provide installation instructions that must be followed for safe, reliable use of the heating appliance.

Follow the instructions in the manual or guide for your heating appliance and also review the installation instructions and bending instructions that came with a replacement thermocouple. 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.The thermocouple on your gas fireplace is a heat-sensitive device that keeps the pilot gas tube open while the pilot is lit.

It does this by generating a small electric current -- on the order of 10 to 30 millivolts -- as a signal to the gas valve. Thermocouples wear out and are replaceable, but you should conduct a few simple tests before doing that, because your gas pilot may be going out for another reason. The thermopile is a related device that you should test at the same time -- its function is to open the gas to the burners. Locate the pilot, often behind a removable grill running along the bottom of the fireplace.

Light the pilot using the recommended procedure for your fireplace. The usual procedure is to turn the gas valve to "Pilot," push in the knob and depress the red ignitor button until the pilot lights. If you have an older fireplace, you may have to light the pilot with a long match. Hold the knob in for 60 seconds, then release it. If the thermocouple is working, the pilot should remain lit. If the pilot goes out, relight it and check the flame.

It should be about an inch in length and predominantly bluish in color, and it should be in contact with the tip of the thermocouple. Clean the pilot tube with compressed air, following the manufacturer's instructions, if the pilot flame is small or intermittent. Move the thermocouple tip closer to the flame if it was not within the flame's reach with the pilot was lit. Relight the pilot and try the test again. Test the thermocouple with a multimeter if the pilot goes out again. Set the meter to measure millivolts and, to make measurement easier, fit the leads with alligator clips.

Locate the gas valve -- it's usually behind a grill on the front of the fireplace -- and find the copper thermocouple wire leading from it. The best way to do this is to follow the wire back from the tip of the thermocouple, which is right next to the pilot light. Leave the pilot end of the thermocouple in place. Attach one lead of the multimeter to the silvered end of the thermocouple wire the part that made contact with the gas valve and the other lead to the bare copper thermocouple wire.As with all my DIY posts, anything you decide to do as a result of reading this post, you do so at your own risk.

With gas and flames involved, things can get dangerous — as in blow-your-house-up dangerous. First, check to see if your pilot light is lit. Recently, I noticed that it was taking a long time for my gas fireplace to light. Because I knew my thermocouple was working fine since the pilot light would stay litI decided to check the output of the thermopile to see how much electricity it was generating.

If they head underneath and up toward the pilot light assembly, those are the TP wires. As you can see from the picture above, my thermopile was putting out. Most thermopiles are designed to generate between millivolts from the heat of a normal pilot light, so mine was well on the low side.

I turned the round knob on the gas valve to the OFF position which killed the pilot light and then closed the shutoff valve on the hose that fed gas to the unit VERY important. I removed the screen and glass cover from the fireplace, and then took a look at the pilot burner assembly.

Gas Fireplace Pilot Assembly. From left to right: thermopile, pilot nozzle, pilot ignitor, and thermocouple. You can also see from the shape of the pilot nozzle that it directs the flame of the pilot light into three directions: left to heat the thermopile, right to heat the thermocouple, and straight ahead to ignite the full burner when the gas valve opens.

I let the pilot heat the thermopile for a few minutes, and then a took another reading:. The output of millivolts shown above was way better than the I started with, and after a couple of minutes I actually saw it climb to millivolts.

The fireplace ignited immediately! I hit the switch a few more times to make sure, and it lit every time. However, when it does eventually become time to replace either of them, just go ahead replace both. Once of my readers shared this video with me, and it does a good job of quickly showing the steps involved in cleaning your thermocouple. You can take out the old ones, take them to any local hardware store, and pick up a generic replacement. Hire a gas fireplace expert if you have any doubts.

I appreciate all the positive comments on this post. And that means you need to read another blog post I wrote. If you feel this article has saved you time or money, you can pay me back by reading my blog post on carbon monoxide poisoning and taking the proper precautions. Thank you! I stumbled across this video today of a server move from a few years ago in I never even How to Clean your Thermopile and Thermocouple. Low millivolts from a thermopile. Better Voltage from the Thermopile.

Read previous post: Moving a Server with Days of Uptime I stumbled across this video today of a server move from a few years ago in For our purposes, we'll refer to both devices as the thermocouple. The thermocouple is part of the pilot burner assembly and connects to the gas control valve on the outside of the water heater. In simple terms, when the thermocouple does not sense flame, it prevents the gas valve from delivering gas to the burner.

It is, therefore, a key safety element of your water heater system. The type of ignition system you have in your water heater will determine how you replace the thermocouple. With both types of ignition—standing pilot or electronic —the thermocouple is part of the burner assembly. With a standing pilot, there is just a pilot and thermocouple attached to the burner assembly. With an electronic ignition, there is a pilot, thermocouple, and electronic igniter attached to the burner assembly.

With electronic ignition heaters, the pilot flame comes on only when the thermostat calls for the burner to ignite. If you have a standing-pilot water heater, skip ahead to step 7: "Standing Pilot Water Heater—Replacing the Thermocouple.

The combustion chamber of water heaters with electronic ignition is sealed tight and gasketed. To access the combustion chamber, you must remove the burner assembly manifold cover, which contains the burner supply tube, burner, electronic ignition, pilot, and thermocouple. Follow these steps to remove the manifold cover:. Once removed, the burner assembly for an electronic ignition water heater should look like the unit shown here. For both electronic-ignition and standing-pilot water heaters: Once the new thermocouple is installed, reconnect the pilot, burner, and thermocouple and electronic igniter for an electronic-ignition unit to the gas control valve as follows:.

Continue to 2 of 8 below. Standing Pilot vs. Electronic Ignition. Tools and Supplies You Will Need Adjustable wrench or open-end wrench Screwdrivers Water-heater manifold replacement gasket if needed New thermocouple if needed. Continue to 3 of 8 below. Disconnecting the Control Valve.

thermocouple placement in flame

Close the shutoff valve on the gas supply piping to the water heater. Remove the cover panel exposing the burner assembly standing pilot or burner manifold cover plate electronic ignition.

Continue to 4 of 8 below. Depending on the brand and model of water heater you have, the panel may be secured by nuts, screws, or specialty tamper-resistant fasteners such as 20 Torx-head screws. Grab the burner supply tube and push down slightly to free the manifold, pilot tube, and thermocouple connections. Take care not to damage the internal components.

Otherwise, remove the gasket and plan to buy a replacement. Clean the metal surfaces between the cover plate and the water heater. Continue to 5 of 8 below. Continue to 6 of 8 below. It should come out easily if you use firm pressure.

Make sure you do not bend or deform the connection between the pilot and the thermocouple bracket. Remove the old thermocouple completely by pulling it through from inside to outside the rubber grommet seal, or by opening in the burner assembly manifold cover. You can cut the old thermocouple, if needed, to remove it. Take the old thermocouple to the hardware, home improvement, or plumbing supply store to buy an exact replacement.

Also buy a new gasket for the manifold cover plate, if you are replacing the old one. Insert the new thermocouple from the outside through the grommet or opening in the burner assembly manifold cover.I've replaced all new parts on a sears gas water heater Thermostate and allthe Pilot goes off after about 15 minutes and will then re-lite after I go thru the motions. A Sears water heater isn't enough info for knowing what model you have and what kind of controls it has.

If it is just a standing pilot type water heater the pilot flame should be the only flame touching the thermocouple.

If you had a leak in the pilot tubing where it connects to the pilot you could have another small flame hitting the thermocouple tubing which impedes how the thermocouple works and drop the pilot out. I have seen this a few times but should be obvious if it is the cause. If this is a sealed type unit they usually have a push button spark-er for lighting the pilot you could be loosing oxygen after the burner lights off.

Different manufacturers use different designs for this. Some screened areas for the air inlet that can get plugged off by lint. This would allow everything to start and light off but would soon snuff out due to a lack of oxygen. Not too long ago I had one that had a spring loaded damper just below the burner that had a pin type plunger with some linkage attached that would spring the damper closed if there was any delayed ignition. The damper had to be depressed and the linkage reassembled.

This damper was not visible only the plunger pin and small linkage could be seen. Doesn't sound a thermocouple. Thermocouple is located in or slightly above the pilot flame.

How to Replace a Water Heater Thermocouple or Flame Sensor

Are you sure thermocouple is the correct part you are looking at? Make sure there is not anything causing a draft. Protect your water heater from drafts. Make sure your flue was installed correctly and is not causing a condition that induces a draft. Here is an example: My wife likes to shut all of the windows when the attic fan is running because she gets cold at night. This cause a draf to come down the flue from outside and blow out the pilot light.

I have a feeling a draft is blowing out your pilot. The thermocouple should be located in the pilot flame. Once it warms up it holds the pilot gas tube open and keeps it lit.

thermocouple placement in flame

That's why you have to hod it for a while for it to warm up and produce a small voltage that energizes a solenoid. Once it's open it should not close unless you lose heat or the flame blows out. I think you have a draft. Sit and watch it for 15 minutes and take note of anything else in your home that changes the instant it goes out.

Could be that your clothes dryer or furnace is piped together with your water heater flue. Answer Save. Gas water heaters are being manufactured with anti explosion type design.

This should be obvious to the experienced eye just by observing the operation.

thermocouple placement in flame

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