Thermocouple for the neva gas water heater. Gas water heater draft sensor. What is a thermocouple

Now we will understand the purpose of a thermocouple in a gas boiler, its features and principles of operation. In the end, we will figure out how to carry out repairs with our own hands.

Any boiler, regardless of the type and principle of its operation, needs a thermocouple - a device that will control the temperature in the combustion chamber and automatically shut off the gas supply when the flame disappears.

For a gas boiler, it is a necessary element in the heating system, which helps to avoid boiler overheating and the possibility of its breakdown.

Gas boiler thermocouple

To understand how a thermocouple works in a gas boiler, you first need to get acquainted with its structure and principle of operation.

A thermocouple is a two-plate conductor structure that consists of different alloys. The device is simple enough, but at the same time reliable.

The principle of operation of this device is based on a physical phenomenon - the Seebeck effect.

The process of formation of an electromotive force at the junction of two dissimilar conductors, the contacts of which have temperature differences. Seebeck effect

If two parts made of dissimilar metals are firmly connected, and the junction is heated, then a potential difference will appear on the cold ends of the soldered conductor - voltage. When voltage is applied, the valve immediately opens automatically, allowing fuel to flow to.

The principle of operation of the thermocouple of a gas boiler

Types of thermocouples

Today, the boiler equipment market is distinguished by an abundance of various thermocouples, which are divided into several types. The metal used in their manufacture is the main criterion on the basis of which they are differentiated.

Of base metals

Thermocouple type	Alloy	Russian marking	Temperature range, ° С	Thermocouple features
K	chromel-alumel	TXA	from -200 ° С up to +1000 ° С	Ability to work in a neutral atmosphere or an atmosphere with an excess of oxygen
L	chromel-copel	TXK	from -200 ° С up to +800 ° С	Highest sensitivity of all industrial thermocouples. Only high thermoelectric stability at temperatures up to 600 ° C is characteristic.
E	chromel constantan	TXKn	from -40 ° С up to +900 ° С	High sensitivity.
T	copper constantan	TMKn	from -250 ° С up to +300 ° С	It can work in an atmosphere in which there is little excess or lack of oxygen. Not sensitive to high humidity.
J	iron constantan	TZhK	from -100 ° С up to +1200 ° С	Works well in a thin atmosphere. The low cost is due to the iron included in the composition.
A	tungsten-rhenium	TVR	above +1800 ° С	Good mechanical properties at high temperatures. It can work with frequent and abrupt heat changes and under heavy loads. Unpretentiousness in manufacturing and installation, as they have little sensitivity to dirt.
N	nichrosil-nisil	TNN	from -200 ° С up to +1300 ° С	It is considered the most accurate thermocouple in the base metal group. High stability at temperatures from 200 to 500 ° C.

Of precious metals

Thermocouple types	Alloy	Russian marking	Temperature range, ° С	Thermocouple features
B	platinum-rhodium-platinum-rhodium	TPR	from +100 ° С up to +1800 ° С	High mechanical strength. Great stability at high temperatures. Slightly prone to grain growth and embrittlement. Low sensitivity to pollution.
S	platinum-rhodium-platinum	CCI10	from 0 ° С up to +1700 ° С	High measurement accuracy. Good reproducibility and stability of thermoEMF.
R	platinum-rhodium-platinum	CCI14	from 0 ° С up to +1700 ° С	Has properties identical to type S thermocouple.

In boiler automation systems, thermocouples of types are often used: E, J, K.

Connection and verification

The thermocouple must be connected with electrodes (wires) made of the same material as the thermocouple to be connected.

Alternatively, metal wires can be used that have characteristics similar to those of the electrodes on the thermocouple itself.

Before connecting thermocouples for heating boilers, it is important to strip the ends of the wires to remove oxides that affect the measurement accuracy. And during installation, it is important to make sure that the fuel return and supply pipes are straight down.

In the event that a thermocouple breaks down, as a rule, it is no longer possible to restore it, so it is important to know how to check a thermocouple with a multimeter on a gas boiler.

The working thermocouple should work after 10-30 seconds of heating

To check its performance, it is enough to connect one end to a multimeter - a measuring sensor, and heat the other end using either a lighter.

A combined electrical measuring device, which can be digital and analog, combines several functions (at least the functions of a voltmeter, ohmmeter, ammeter). Multimeter

The working thermocouple should have a voltage in the region of 50 mV.

If the thermocouple is faulty, you can replace it yourself.

DIY thermocouple repair

To fix the problem with your own hands, you must:

unscrew the clamping nut with a wrench and remove its end;
lacing-zero to clean from dirt;
check the thermocouple with a multimeter;
make sure that all indicators are in accordance with the norms;
reassemble the thermocouple and start the boiler.

If the thermocouple cannot be repaired, then there is always the opportunity to buy a new one. The Russian market offers a wide range of these devices produced by various manufacturers, for example, ABAT, AOGV, AKGV. Their price ranges from 300 to 2000 rubles. For gas boilers of foreign production (for example, Bosch, Viessmann, Vaillant), the price of a thermocouple will be higher.

Today thermocouples are actively used in, the choice of them on the market is great, and everyone has the opportunity to purchase a universal thermocouple. However, choosing a thermocouple yourself can face a number of difficulties. You should contact a specialist who will tell you how to choose a device that meets all the characteristics of a gas boiler. You can also use the table of dependence of the technical characteristics of the device with the characteristics of the gas boiler.

Content

Device, principle of operation and main types
Thermocouple in the gas control system (gas control)
Connecting, checking and troubleshooting

Introduction

The use of gas for heating a private house or cottage is very convenient and cost effective. However, this type of fuel is fraught with a serious threat. If, for any reason, the burner suddenly goes out and the gas supply is not shut off in time, a leak will form and this can turn into serious trouble and endanger the lives of people in the room. In order to immediately shut off the gas if the flame is suddenly extinguished and a thermocouple is used for a gas boiler.

In this article we will talk about what a thermocouple is, why it is needed and how it works, we will consider the main types and most common malfunctions associated with these devices, as well as a method for eliminating them.

Device, principle of operation and main types

Thermocouple is a classic thermoelectric transducer that is used to measure temperature in various fields of industry, science, medicine, as well as in automatic control and monitoring systems for gas boilers, stoves and columns.

It is arranged very simply and can easily be made by yourself. Two conductors of different materials are connected in a ring. One of the connection points is placed in the measurement area, and the other is connected to a measuring device or a converter device.

Photo 1: Thermocouple for gas control device

The principle of operation of a thermocouple is based on the thermoelectric effect, or as it is also called the Seebeck effect. It consists in the fact that a voltage appears at the junction of two conductors of different metals connected in a ring. If the temperature of the soldering points is the same, the potential difference is zero. But as soon as one of the junctions is placed in an area with a higher or lower temperature, a voltage other than zero appears and is proportional to the temperature difference. The coefficient of proportionality is different for different metals and is called the coefficient of thermo-EMF.

Photo 2: Design and principle of operation of the thermocouple

The main materials for the manufacture of thermocouples are precious and non-precious metals. Most of the alloys of them have rather exotic names, which are very popular among the compilers of various crosswords and scanwords. There are several types of thermocouples depending on which metal pairs are used in the manufacture. Below is a table with their main types, designations and characteristics:

In automation systems for gas water heaters, stoves and boilers, thermocouples TXA from chromel-alumel (type K), THK from chromel-copel (type L), TLC from iron and constantan (type J) are usually used. Sensors made of precious metal alloy are designed for high temperatures and are mainly used in foundries and other heavy industries.

Photo 3: Sakhalin gas burner for heating boilers and furnaces

Some models that run on solid fuels, for example, such as can be equipped with gas burners, in which thermocouples are used to protect against gas leaks.

Back to the table of contents

Thermocouple in the gas control system (gas control)

Once you decide, you don't have to worry about what happens if the fire suddenly goes out. However, when you use gas equipment, you need a non-volatile automation that can shut off the gas supply as quickly as possible if the burner suddenly goes out. For these purposes, a gas control system is provided in modern gas boilers. How does it work?

The system consists of two main parts: a solenoid valve and a thermocouple. One end of the sensor is placed directly in the burner flame, and the other is connected to the solenoid valve, which consists of a core with a winding, a cap, a return spring, an armature and a rubber band that blocks the gas supply.

Photo 4: Non-volatile gas control system for stoves and boilers

Gas control works quite simply. By pressing the gas button, you push the stem inside the coil, charging the spring. According to the instructions for igniting a gas boiler, the supply valve must be held pressed for about several tens of seconds. This time is necessary in order for the thermocouple to warm up and there is enough voltage at its ends to hold the valve inside the coil.

At the moment when the burner goes out, the thermocouple begins to cool down, the voltage at the ends of the thermocouple decreases and at some point, the return force of the spring outweighs the electromagnetic force holding the stem inside and returns the valve to its original position, shutting off the gas supply. This process usually takes several tens of seconds.

One of the features of gas control is that it is completely electrically independent. In large heating systems like this, when the power supply is cut off, the entire control system ceases to function. The thermocouple gas control system is completely electrically independent, and is able to function reliably without the need for an electrical connection.

Company manufacturer:

Description Thermocouple for gas water heater Neva 5014, 5013:

Delivery for you anywhere in Russia ... delivery. ... Russian Post ().
Product weight in package: 1 kg - specify for

Distinctive features of Thermocouple for a gas column Neva 5014, 5013:

Thermocouple for gas water heater NEVA 5014

In the heating equipment store, you can buy a thermocouple for a gas water heater Neva 5014, 5013 at a price of 800 rubles!

Similar Products to Thermocouple for gas water heater Neva 5014, 5013

Reviews about gas water heaters of the TechnikSAN online store

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Thermoelectric sensors - thermocouples - are used especially in gas boilers and water heaters equipped with non-volatile safety automation. The task of the element is to monitor the presence of a burner flame by continuously supplying voltage to the solenoid valve of the SIT 630 control unit (or similar). Our goal is to tell you what a thermocouple is, how it works and how it changes in the event of a malfunction.

Thermoelectric flame sensor device

The thermocouple is a safety element of a gas boiler that generates voltage during heating and keeps it open while the igniter is on. The sensor shown in the photo operates autonomously, without connecting an external power supply. The scope of application of thermocouples is gas-powered non-volatile installations: ovens, kitchen stoves and water heaters.

Let us explain the principle of operation of a thermocouple for a boiler, based on the Seebeck effect. If you solder or weld the ends of 2 conductors from different metals, then when this point is heated, an electromotive force (EMF) is generated in the circuit. The potential difference depends on the temperature of the junction and the material of the conductors, usually in the range of 20 ... 50 millivolts (on household appliances).

The sensor consists of the following parts (the device is shown in the diagram below):

thermoelectrode with a "hot" junction of two dissimilar alloys, screwed with a nut to a mounting plate next to the boiler pilot burner;
extension cord - a conductor enclosed inside a copper tube, simultaneously playing the role of a negative contact;
positive terminal with a dielectric washer, inserted into the socket of the automatic gas valve and secured with a nut;
There are types of thermocouples that are connected to the automation using conventional screw terminals.

In this model, the heated electrode is attached to the boiler plate without a nut - inserted into a special groove

Note. A copper tube is needed to protect the positive conductor from external noise generated by the house network 220 V and other electrical appliances. Remember, the minimum voltage for a thermocouple is only 20 mV.

For the manufacture of electrodes that generate EMF, special metal alloys are used. The most common thermal vapors are:

chromel - alumel (type K according to the European classification, designation - TXA);
chromel - copel (type L, abbreviation - THK);
chromel - constantan (type E, designated as THKn).

The principle of operation of a thermal pair from two different alloys

Reference. Alumel is an alloy of nickel with aluminum, manganese and silicon. The composition of chromel is 90% nickel, 10% chromium. Copel also includes nickel combined with copper and silicon.

The use of alloys in the design of thermocouples is due to the better generation of current. If you make a thermal pair of pure metals, the output voltage will be too low. Most heat generators operated in private houses are equipped with TXA (chromel - alumel) sensors. For more information on the device of thermocouples, see the video:

The principle of operation as part of the boiler

The connection diagram of a thermoelectric sensor in various gas-using devices is approximately the same. The measuring electrode is located in the area of the wick or the main burner, the conductor is connected to an electromagnet that opens the gas supply.

Reference Information. In turbocharged and atmospheric heat generators connected to the household power grid, a photoelectric sensor can be used instead of a thermocouple. It detects the presence of fire without direct heating.

How does a thermocouple work on the AOGV type and similar devices:

The user presses the button with one hand and forcibly opens the gas supply solenoid valve.
With the other hand, the homeowner turns on the piezo ignition while holding the first key. The igniter flashes.
According to the operating instructions, the button must be held for 5-30 seconds (depending on the model of the unit), during which the wick heats up the measuring electrode.
In the electromagnet circuit, a direct current is generated from the thermoelectrodes. The user releases the key, but the fuel supply does not stop - the valve now holds the thermocouple voltage.

If, for various reasons, the fire goes out, the heating of the thermoelement ends, the EMF will disappear. The electromagnet will turn off, the spring will close the valve and block the path of the fuel.

Reference. Gas water-heating installations, independent of electricity, are equipped with automatics from various manufacturers - EuroSIT, Zhukovsky plant, "Arbat", "Orion" and so on. The thermocouple works on the same principle everywhere - while the electrode is heated by the flame, the gas supply will be open.

The thermocouple electrode is located next to the igniter on all water heaters

Differences from temperature sensor

In addition to the thermocouple, a thermocylinder is connected to the automatic fuel valve of the boiler, which is responsible for turning off the main burner when the set temperature of the coolant is reached. Externally, the flasks of the elements and the copper connecting tubes are slightly similar. An uninformed homeowner can easily confuse these sensors.

Let's list the main differences between a temperature meter and a thermocouple:

sensor design - a cylindrical bellows made in the form of a copper flask with a sealed end;
the thermocylinder is connected to the gas automatics with a thinner capillary tube than the power-generating sensor;
the thermosensitive bulb itself is installed inside the immersion sleeve or hides under the casing near the water jacket, and is not attached near the igniter;
the temperature meter is not disconnected from the automation at all or differs in the size of the fastening nut.

Note. The thermocylinder works according to a different principle: when heated, a special liquid expands inside the flask. The capillary pressure is transferred to the automation valve, which turns off the main burner. The pilot flame is not extinguished.

How to check and replace a thermocouple

The main symptom of a flame sensor malfunction is that the wick goes out simultaneously with the release of the button. Sometimes the problem manifests itself differently - the light on the igniter remains, but after the main burner is ignited, the fuel supply is again shut off and completely. The reasons for such problems:

the thermal electrode is covered with soot and does not heat up well, which causes the voltage in the circuit to fall below the minimum;
burnout of the meter body;
violation of contact at the point of "hot" junction;
the fastening nut has been unscrewed, the working rod is warped and does not warm up well with the igniter;
the traction sensor has become unusable or its electrical circuit has been broken.

The electrode heated by the igniter must be periodically cleaned of carbon deposits. The problem is that the contamination of the part is poorly visible from the outside, you have to remove the bar or the entire panel with the burner

Clarification. A malfunction of the draft sensor causes similar symptoms, since this "limit switch" is connected in series with the thermocouple (in the open circuit). To eliminate the influence of the sensor, temporarily short-circuit its wires.

For diagnostics, you will need a multimeter or other device capable of measuring low voltage (up to 100 mV). How the check is done:

Main condition: a working thermocouple for the boiler must produce a voltage of at least 0.02 volts. If the device shows zeros, the voltage jumps or does not exceed 20 mV, the element must be changed. Modern sensors cannot be repaired by soldering.

Advice. When buying a new thermocouple, always be guided by the brand and specific model of the boiler, so as not to get confused in the markings and designations.

If you do not want to remove the element ahead of time, diagnostics can be performed directly on the boiler. After unscrewing the nut, disconnect the thermocouple tube from the automation and connect the multimeter as described above. While holding the key, light the igniter and read the instrument. Disadvantage of the method: impossibility of visual inspection and cleaning of the electrode from soot.

When installing a new thermocouple in the gas boiler, adjust the position of the heated rod. Ideally, the electrode stands horizontally, does not tilt up or down, and is well washed by the flame of the wick.

Conclusion

Knowing the boiler thermocouple device and how to check it, it is easy to identify the problem, as well as replace the sensor at home. It is important to cut off other malfunctions here - breakdown of the traction sensor or the solenoid coil. The latter malfunction is typical for domestic models of automation - "Arbat", ZhMZ and so on. How to make repairs with improvised means, see the last video:

The temperature in the combustion chamber of an operating boiler plant is high enough and can be measured using a thermoelectric element (thermocouple). This element is almost the only means of measuring high temperatures used in many areas of our life. In this case, we will talk about such a variety as a thermocouple for a gas boiler, working in conjunction with an automatic gas valve.

The device and principle of operation of the thermocouple

Indeed, not every material can constantly be in the open flame zone. The thermoelement is made of metal, more precisely, of several metals, so it is not afraid of high temperatures. When operating a gas boiler plant, you cannot do without it; failure of a thermocouple means a complete shutdown of the unit and immediate repair. The thing is that the thermoelement works in conjunction with an electromagnetic shut-off valve that closes the entrance to the fuel path. As soon as this part fails, the valve closes, the fuel supply stops and the burner goes out.

To better understand the principle of operation of a gas boiler thermocouple, it is worth considering the diagram shown in the figure.

This principle is based on the following physical phenomenon: if you reliably connect 2 dissimilar metals together, and then heat the junction, then a potential difference will appear at the cold ends of this junction, that is, voltage. And when a measuring device is connected to them, the circuit will close and a constant electric current will arise. The voltage will be quite small, but this is quite enough for induction to occur in the sensitive coil of the solenoid valve and it opens, allowing the fuel to pass to the igniter.

For reference. Some modern solenoid valves are so sensitive that they remain open until the input voltage drops below 20 mV. The thermoelement in normal operating mode generates a voltage of the order of 40-50 mV.

Accordingly, the device of the thermocouple of a gas boiler is based on the described phenomenon, which is called the Seebeck effect. Two parts made of different metals are firmly connected to each other at one or more points, and the quality of the connection plays an important role. It affects the operating parameters of the element and the durability of its operation. The junction will be the same working part placed in the open fire zone.

Since many different pairs of metals are used for the manufacture of thermoelements, without going into details, we note that a chromel - aluminum pair is used in a thermocouple for a gas boiler. Conductors enclosed in a protective sheath are welded to the cold ends of these metals. The other end of the conductors is inserted into the corresponding socket of the unit automation and secured with a clamping nut.

In the process of igniting the igniter and burner of a gas boiler to supply fuel, we open the solenoid valve manually by pressing on its stem. The gas enters the igniter and ignites, and the thermocouple is nearby and heats up from its flame. After 10-30 seconds, the button can be released, since the thermoelement has already begun to generate voltage that keeps the valve stem open.

Advantages and disadvantages

Due to the fact that it is quite simple and inexpensive to manufacture a thermocouple, it has become an indispensable element of automation and control in gas-powered equipment. In addition, there are other advantages of these products:

Acting as a flame control sensor, the thermoelectric element can also work as a temperature sensor.
The absence of moving parts, complex components and expensive materials makes the product inexpensive and durable.
Wide range of measured temperatures.
Sufficient measurement accuracy, allowing the use of this device in heating technology.
The ease with which a thermocouple is installed or replaced in a gas boiler.

Among the disadvantages of thermoelectric sensors, it can be noted that the increase in the potential difference is not proportional to the increase in temperature, that is, the dependence is nonlinear. In addition, the voltage rise has a limit and it is not large; in a thermocouple of gas boilers, its value reaches 50 mV. These properties of the product do not create problems when interacting with the shut-off device, but when measuring temperature, such a weak and non-linear signal requires amplification and calibration.

The simplicity and reliability of the design of the thermoelectric sensor also have a negative side. When this element fails, which sometimes happens due to poor-quality junction performance, then repair of the thermocouple is impossible. The product may simply burn out and there is nothing to repair there, all that remains is to replace it, and as quickly as possible, since the gas boiler will not work without a thermocouple. But there shouldn't be any special problems, the device can be easily removed and disconnected, and its price is not at all high.

Advice. Sometimes a thermocouple stops working just because there is a weak connection at the junction. It is necessary to loosen and unscrew the clamping nut, remove the conductor from the gas valve and very carefully clean its end, and then collect everything back.

Conclusion

Despite its simple design, the thermoelectric element is one of the most important parts of any modern gas boiler. It acts as a temperature and flame sensor, ensuring the safe operation of the heater. In the event that the pilot is damped or the temperature rises, the thermocouple will respond to voltage changes and trigger the shut-off valve.