Where To Buy A Thermocouple For Furnace

Where To Buy A Thermocouple For Furnace

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When your pilot light is lit, the heat from the flame sends a voltage through the thermocouple that keeps the gas line open. If the pilot light goes out, the thermocouple will lose its voltage and the gas line to your furnace will be closed.

There are a couple of things that can go wrong with thermocouples that prevent them from operating properly. One of the most common issues is that the thermocouple can get dirty. This will cause the thermocouple to make improper readings, which can shut off the gas supply to your furnace prematurely or prevent gas from reaching your furnace in the first place. In addition, wires can become loose or the thermocouple may need to be recalibrated. Many of these issues can be prevented by changing your air filter and scheduling annual tune-ups.

High-temperature applications that reach up to around 2900°F use the Type S thermocouple. Lower temperature processes also use Type S thermocouples because of its accuracy and stability. High-temperature procedures, especially in the biotech or pharmaceutical industries, most frequently use the Type S thermocouple. Like all platinum-type thermocouples, always use a ceramic tube to protect the Type S thermocouple.

Like the Type S, the Type R thermocouple is used in high-temperature applications reaching up to 2900°F. However, never use the Type R in reducing atmospheres. And as an all platinum-type, a ceramic tube should always protect Type R thermocouples.

Temperature applications of up to around 3200°F use the Type B thermocouple. Use this platinum-type of thermocouple in oxidizing or inert atmospheres with applications ranging from 1000°F to 3100°F. Never use Type B thermocouples in reducing atmospheres. Always use a ceramic tube to protect this type of thermocouple.

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.

Don't confuse a thermocouple (discussed here) with a different type of temperature sensor, solid-state THERMISTORS used in thermostats. 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.[3]

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.

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. [Click to enlarge]

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

If a thermocouple is used you'll see a small copper tube (or in some devices an electrical wire) connecting the flame sensor to the valve.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.

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.

At THERMISTORS we explain the differences among a thermocouple, thermopile and thermistor in more detail. 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 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 is provided with the connecting tubing coiled neatly in a package. Don't be afraid to un-coil the tubing into a more straight line to ease installation of the device. But do not nick, kink, nor make sharp bends in the tubing.

Doing so will almost certainly make it inoperative and thus unsafe. If your gas fired equipment also uses an igniter wire in addition to the thermocouple, they are often routed together and will need to be removed for thermocouple replacement. Take care not to damage the igniter wire and to reconnect it just as it was.

Installation steps for installing a replacement thermocouple are simple, and are made easier by looking carefully at how and where the old thermocouple was installed and where and how its tubing was routed between the gas valve and the flame sensor position. You can make your job easier by shutting off the gas supply and removing the old thermocouple intact to help select a replacement model.

GAS LP & NATURAL GAS SAFETY HAZARDS Watch out: Do not turn on nor try to use gas fired equipment if there is a gas leak. Doing so risks fire, explosion, injury, even death. How to Troubleshooting Thermocouples on Gas Fired Heating EquipmentFirst confirm that the problem is the thermocoupleTypically the gas control is pushed-in or held in a spring-loaded position to force gas through the pilot light assembly to permit manually lighting the pilot flame.

If you are able to light the pilot on the gas fired appliance but when you release the gas control from it's "LIGHT" position the pilot immediately goes out, if there was a good solid flame that was clearly touching and heating the thermocouple, that is, the thermocouple was properly positioned in the pilot flame, and if you are sure that you held the control in the LIGHT position long enough for the thermocouple to heat up normally (30 seconds is plenty), then I suspect that the thermocouple is defective.

Watch out: Before trying a new thermocouple I'd suggest checking for debris in the pilot light orifice or tubing. 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.

We have run into this problem and also read other accounts of it concerning the Gaffers and Sattler 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.(Gaffers and Sattler was an appliance brand (kitchen ranges, heating equipment, air conditioning) owned by Maytag and actually preceded "Maytag" as a company name.The Gaffers Sattler and Maytag Washing Machine Company was founded in 1893 by businessman Frederick Maytag. G&S cooking ranges were identified as a subsidiary of MagicChef in 1969. Magic Chef found its way back to Maytag in 1986.

On these appliances there may still be a thermocouple to confirm that there is a good gas flame when the burner is on - since we don't want to continue supplying gas if there is no flame (doing so risks an explosion).

The thermocouples used in building mechanical systems are generally type K: thermocouples used in heating boilers, calorifiers, geysers, gas burner applications (flame sensors). Type K thermocouples are widely used in industrial applications involving water, mild chemical solutions, hospitals and the food industry.

@Don, I don't know, Don, but there are some possible explanations I can suggest for the frequent replacement of a thermocouple on a gas fired Heating system. One is that the thermocouple is not being correctly placed in the gas flame and is being replaced as defective when really it's an installation error. Next is a similar error in which the installer doesn't adequately tighten the connection of the thermocouple at the gas valve. Again we find that sometimes installer makes the same mistake repeatedly so we keep replacing the part. A third is that all of the thermocouples were bought from the same manufacturing run or a lot and is it effective product. One thing to try is being sure to go to a completely different source. Finally we want to make sure that the problem is really the thermocouple and that we're not blaming it for another problem on the heating system.

@Simon, We need to find and read the product description and instructions for that thermocouple before commenting further. Follow up here. If you could post a photo that would be helpful.

Why does it need this because if there is no heat on the thermocouple then the gas will not flow? I assume this is an 'extra' safety feature that changes the thermocouple price from £10 to £80+? why is thermocouple wire always in a copper tube?

@Diego, That's an interesting question. We're in the realm of OPINION here, as I haven't found authoritative research data on abrasion or oxidation damage to the thermocouple tubing where it passes through appliance openings. Post some sharp photos (one per comment) of your old thermocouple so that we can see what you see and perhaps a photo as well of how the tubing passes through parts of your gas oven. The typical thermocouple installation instructions given on this page at _Replacement.php#ThermocoupleInstall do discuss routing. The tubing needs to be protected from mechanical damage, and extra length safely coiled and placed out of harm's way. Needless to say experts have researched thermocouple failure. I'll add some of that to the article above. thanks for asking 781b155fdc