The hot water in a two-circuit boiler is turned off

Boiler operating principle

To understand the causes of failure, you need to understand how the boiler works. Two-circuit devices “Ariston”, “Baksi” and other models have several units. In the gas node occurs ignition and combustion, the water node is responsible for water supply and pressure in the main. Smoke extraction unit takes the products of combustion outdoors.

water, two-circuit, boiler, turned

As soon as you start the boiler, the pump is triggered, which pumps water into the system. The gas valve opens. Liquid circulates through the tubes of the heat exchanger, and the burner evenly heats its body. Sensors monitor the heating process. As soon as the temperature reaches the set point, the gas supply is shut off, the heating stops.

When the temperature starts to drop, the sensors send a signal to the control module. the heating cycle starts again.

A flow sensor is triggered when the faucet is opened. This gives the board a signal to switch the three-way valve to DHW heating. When the faucet closes, the valve shifts to the heating system. Some models are equipped with a “quick start” mode. Then the valve periodically switches, heating both the first and second heat exchanger.

The DHW is not heating. causes and troubleshooting.

The most common reason why DHW doesn’t heat is the amount of limescale that builds up inside the heat exchanger. Limescale not only narrows the water flow in the heat exchanger, it also significantly reduces the water temperature.

The reason is the thermal conductivity of scale salts is many times less than the thermal conductivity of the metal of which the heat exchanger is made. The unit does not give (does not deliver) hot water or it does not run well, if a piece of plaque broke off and blocked the flow of liquid.

No hot water in the faucet when the flow sensor does not trip. It is a fan, which operates when the water flows through it. The signal from it goes to the control board, it gives the command to heat the water. The sensor can be clogged and can be cleaned without having to dismantle it.

The sensor is a cylinder located near the circulation pump. To clean, simply open and close the faucet in front of the unit. If this procedure is unsuccessful, it will have to be dismantled, cleaned and put back in its original place. If the sensor is faulty, you will have to replace it.

If the three-way valve is defective, the unit does not deliver hot water. The purpose of the three-way valve. to shut off the heating system when you open the tap with hot water. When the valve does not switch, the boiler continues to heat water for heating.

The cause of valve failure can be a simple clog, such as a piece of rust. If the problem is more serious, replace the valve with a new one. In addition, one of the simple reasons why the tap does not run hot water can be clogged gas hoses or a gas filter.

Three-way valve in section

In heating it will not be so unnoticeable, but the temperature of water from the faucet will be felt more significantly. Clean the hose and filters. Some of the above issues may also be the causes of problems with heating and hot water in wood-fired, electric and solid fuel (CT) boilers, subject to similar design details.

Two-circuit boiler: does not turn on hot water. 5 reasons

Most often, problems with the boiler is detected when the heating season comes, the period when both circuits of the device work. It’s worth considering two key problems that gas wall convector owners may encounter, namely:

The system works, the unit turns on, but the water heats weakly or does not heat at all.

The gas convector does not start and, as a consequence, there is no hot water supply.

Each of these problems has its own causes and solutions. To eliminate the problem there is no need to find out what caused the problem. Before identifying faults of the equipment, it is necessary to study the manual, read it and check if the device is set up and connected correctly.

Modern gas boilers are equipped with a diagnostic system that can detect malfunctions and displays the error code. Your machine manual can help you decipher the codes. While complying with all the requirements and conditions, the most common causes of malfunctions must be considered. If the boiler does not work for heating and hot water supply, then often the cause of these problems may be the same.

Clogged heat exchanger tubes. Many experts say that, using unfiltered working fluid increases the risk of clogging in the heat exchanger tube. The resulting buildup can reduce heat conduction, causing the equipment to run excessively, consuming energy. Then the optimum temperature is not even reached when the device is running uninterrupted. Due to the settled plaque inside the heat exchanger, the metal succumbs to corrosion and this can lead to destruction.

Defective pump. The circulation of the coolant can be stopped due to a build-up of air, known as an air lock in the pump. The second cause of pump failure can be a seized rotor. Stopping the circulation pump can cause the gas boiler to overheat.

Flow sensor clogged. Inside the boiler there is a turbine-shaped sensor that resembles a small fan. When the turbine rotates inside the sensor, an electrical pulse is generated due to the flow of liquid, which is fed to the control unit. Thus, the electrical system understands that it is necessary to heat the coolant.

Three-way valve jams. This kind of failure does not allow you to switch the water supply from heating to hot water. Stopping the valve often happens because of clogs occurred both the element itself and the gas hose or filter.

Not enough pressure. If the volume of liquid in the system does not create the necessary pressure, the water valve does not open, which leads to the inability to ignite the burner.

Consider possible solutions to the problem. When you know the reason why the boiler does not heat water, you can try to fix it yourself. Manufacturers often provide mechanical units for self-service.

Important! If you find the fault on your own, before you start the work, disconnect the unit from the power supply and free the internal components from the coolant.

It is not easy to find out prematurely about the presence of malfunctions. But if you find a problem, it is recommended to contact a specialist, who will help to eliminate existing problems and give sound advice on the proper operation of gas equipment.

For a clearer understanding of the situation you need to understand the principle of the boiler. Such two-circuit gas wall boilers such as “Baksi” or “Ariston” consist of several components. The gas part is responsible for burning the incoming fuel, the water part provides the supply of heated water from the heat exchangers in the heating system, the smoke exhaust part is responsible for removing the products of combustion outside the home.

Depending on the user’s settings, temperature sensors set the mode of water heating. Sensor on the return pipe turns off the boiler, depending on reaching the required temperature set for the return. However, the system pump does not stop working until the temperature of the heat exchanger decreases.

This is provided so that there is no boiling of water in it. As soon as the coolant cools to the limit, the electronics will send a signal to turn on the pumping of water and gas valve. The whole process will start again. When opening the tap in the faucet in a two-circuit boiler, the flow sensor reacts, which informs the electronics of the need to switch the three-way valve to the mode of heating water for DHW.

When you turn off the hot water tap there is a reverse transition to heating mode. Some manufacturers provide for heating both heat exchangers during periodic switching.

The dual-circuit boiler is set to maintain a certain temperature in the hot water circuit. When you turn on the hot water at one of the points:

  • For some time cold water continues to flow from the tap, which was in the pipe before it was opened,
  • Preheating of the boiler starts, and it takes a certain time for it to reach the desired temperature,
  • After a few seconds the heated water flows into the pipe and begins to move to the point of intake,
  • a few seconds more are needed for hot water to reach the extraction point,
  • an extra few seconds are needed because the incoming water seems too hot for the user, and the user adjusts the water flow with the faucet.

Thus, at least a few seconds elapse between opening the hot water tap and the start of water supply at a comfortable temperature. The farther the water intake point is from the boiler, the longer this time interval is.

All this time the user can not fully use the water, and he will be that the boiler does not properly heat hot water. He is waiting for comfort temperature water to arrive. Meanwhile the water that is not at a comfortable temperature for the user simply goes down the drain.

Non-productive consumption of water can be from a few liters to ten liters, depending on how far the water intake point is from the boiler.

Is cold and hot water coming out of the boiler, what to do?

How to eliminate the clocking of the gas boiler in DHW mode For heating and hot water apartments and small private homes with one bathroom are usually used dual-circuit gas boilers. The owners of such boilers are often faced with the fact that from the faucet is running cold and hot water. As they say in the popular boiler taktuyut, boiler DHW mode is periodically off, then on again.

Described in this article the principles of adjustment, adjustment of the hot water system is suitable for two-circuit gas boilers of many brands and manufacturers, as well as gas water boilers.

Why is there cold and then hot water coming out of the boiler?

Double-circuit gas boiler in the hot water supply mode (DHW) operates at maximum capacity. For example, the Protherm Gepard 23 MTV boiler manual states that with the factory settings of the maximum output of 23.3 kW., the boiler heats water at a temperature difference dT=30 oC, at a maximum flow of hot water of 11.1 l/min.

Modern faucets are designed with water conservation in mind. For example, in a house connected to the central water supply system, the following results were obtained measuring the maximum flow of water: through the shower screen 6 l/min., wash basin horn 4 l/min., in the kitchen sink 5 l/min.

Normally, users do not open the water draw-off valves to the full flow rate in order to save money. In addition, in order to obtain a comfortable temperature, hot water is always mixed with cold water.

The boiler burner in DHW mode turns on at a flow rate of 1.5 l / min. Turns off at 1.1 l/min. This hysteresis is a protection against periodical switching on/off of the burner at fluctuations of the flow rate.

Taking these factors into account, the actual amount of water that should heat the boiler in a minute will be approximately 1.1-4 liters / min.

Obviously, the difference between the factory set maximum capacity of the boiler, designed to heat 11.1 liters per minute, and the power required to heat the actual flow at the water tap will be significant. Boiler burner power within certain limits is regulated by the automation. But the huge difference between the maximum output, and the power used to heat the actual flow of water, leads to the fact that the boiler automation is unable, without additional settings, to bring the boiler power to meet the needs of the DHW system.

A large excess of the factory set maximum output of the gas boiler in DHW mode over the power required to heat hot water in the water taps at users, leads to cycling (beat) of hot water heating. Boiler burner in the domestic hot water mode periodically turns on and off. Accordingly, from the tap comes alternately cold and hot water.

Setting, adjustment of the hot water temperature in the DHW system

The diagram of tap water heating by a two-circuit gas boiler depending on the temperature (T oC) and flow rate (Q l/min) of hot water. Working area. the boundaries are shown in bold line. Grey zone, pos.1. Boiler clocked zone (switching between ON/OFF and ON/OFF mode)./OFF.).

For normal boiler water heating, on the diagram, the temperature and hot water flow crossing point (operating point) must always be within the working area, which boundaries are shown on the diagram with a thick line.

If the hot water consumption mode is selected in such a way that the operating point is in the grey zone, pos. 1 on the diagram, the boiler will cycle.

From the diagram you can see that the boiler does not work in the gray area, to eliminate the beat at a low flow of water, the temperature of water heating is better to set the maximum, 60 oC.

As mentioned above, the house does not need to prepare large streams of hot water. It is much more important to provide comfortable use of hot water at a low flow rate. To this end, the working area in the diagram should be moved to the left. You can do this by reducing the maximum power of the boiler burner, reducing the gas flow by adjusting the gas valve.

Secondary Return Hot Water. How Does It Work. Central Heating Systems.

How not to fight with tact

How to fix your heating or hot water when it overheats and the boiler will not turn off.

Some “experts” advise to set the temperature of hot water lower, no more than 50 oC, in order not to dilute the water in the mixer during water intake, and open the faucets at full flow. Thus, they suggest to get rid of beat, maximizing the flow of heated water. In many cases this really helps, as the water flow rate and temperature fall into the operating range on the chart.

In systems of DHW with a two-circuit boiler or a gas water heater do not advise to do so, and here’s why. With this method you have to use a lot more water, and therefore gas, than necessary. In addition, the need to always keep a large flow of water from the faucet, the inability to regulate the water temperature. all this creates a discomfort of using hot water.

In addition, the display of a two-circuit boiler does not show the temperature of hot water at the outlet of the boiler, but the temperature of heating water at the outlet from the primary circuit of the heat exchanger for DHW (return temperature from the heat exchanger for DHW).

In systems with a two-circuit boiler, the automation keeps the temperature of the heating water at the outlet of the primary circuit of the HWW exchanger constant (return temperature from the HWW exchanger), and the temperature of hot water at the outlet from the secondary circuit of the HWW exchanger is not regulated.

The temperature of hot water at the boiler outlet will be as it will be, depending on the degree of opening of the water tap, the water temperature in the water supply system, the thickness of the scale layer. That means that every time you open the water tap, the hot water temperature will be different.

Therefore, the required temperature of hot water at the boiler outlet cannot be preset on the display. If you set the temperature of heating water on the display, for example, 50 oC. then the temperature of hot water from the tap will always be less, and less each time is different.

In the DHW system with a two-circuit boiler, the water temperature is more convenient to regulate directly at the tap at the time of discharge, mixing in the mixer with cold water. To have such a possibility, you need to have some reserve of water temperature at the boiler outlet.

For comfortable use of hot water from a two-circuit boiler must be set and set on the display in DHW mode to the maximum temperature of 60 oC.

Setting the maximum output of the boiler burner in DHW mode

In order for the boiler in the mode of DHW heating water evenly, not tapping even at the minimum flow of water, it is necessary to make the maximum power of the burner less, reducing the gas supply by setting the gas valve. The entire working area in the diagram will move to the left.

As a result of adjusting the gas valve, there will be no signs of burner malfunction in DHW operation, when the flow rate of hot water changes over the whole range, from the maximum (6 l/min) to the minimum, specified in the manual (1,1 l/min). The temperature of hot water can be regulated by the mixer, changing the flow of water and mixing it with cold water in a limited, but quite comfortable range.

Setting, adjustment of the SIT gas valve

SIT Gas valve. 1. gas pressure test connection on valve outlet, in front of burner; 2. maximum gas flow rate adjustment nut; 3. minimum gas flow rate adjustment screw; 4. adjustment device cover; 5. gas pressure test connection on valve inlet, in gas network.

Manufacturers of two-circuit gas boilers of many brands install a gas valve of the Italian company SIT on the boilers. The maximum and minimum settings of the boiler burner output are performed by turning the adjustment screws located on the valve body.

Adjust the gas pressure before the burner in the DHW mode:

  • It is obligatory to set the temperature of hot water on the boiler display to 60 oC. (for setting the DHW temperature, see above).
  • Remove the regulator cap (pos.4 in the figure).
  • Turn on the boiler in domestic hot water mode, opening the hot water tap at full flow with the maximum water flow rate.
  • Set (decrease) the gas pressure in front of the burner by means of the maximum gas flow regulation screw (pos.2). Turning to the right increases the gas flow rate, turning to the left reduces it. Visually inspect the flame height in the boiler burner. The purpose of the adjustment is to reduce the gas supply to the burner so that the burner operates continuously and the temperature of hot water from the tap remains constant and comfortable.

Controlling the gas pressure in the network

The gas pressure in the gas network may drop below the permissible pressure for the boiler operation. It is necessary to check the pressure from time to time, especially in frosty weather, when the gas consumption in the network is at its maximum.

At the boiler inlet, static pressure and dynamic pressure are measured. Static pressure is when the boiler does not consume gas. Dynamic pressure measured at maximum gas flow rate of the boiler.

The pressure in the gas network, at the gas valve inlet, is measured by connecting a gas sampling hose with pos.5 Connect the pipe of the U-manometer. To measure the dynamic pressure, open the hot water valve to the full flow.

Normal dynamic gas pressure at the gas valve inlet must be within the range 1.3. 2.5 kPa (13. 25 mbar or 132. 255 mm). water. st.). If during measurement the dynamic pressure value is out of the indicated limits, contact the gas-handling service

How to measure the gas inlet pressure and adjust the minimum and maximum gas pressure at the outlet of the SIT gas valve, see this video.

The tap in DHW mode is eliminated by reducing the maximum pressure. To do this turn the adjusting nut counterclockwise.

U pressure gauge

It is possible to tighten 8 mm tubing of inner diameter on the gas valve socket. For pipes of a different diameter you need an adapter.

After having finished the measurement, do not forget to carefully screw in the test connection and check the test connection for leak tightness.

Adjustment, adjustment of the SIT gas valve

SIT Gas Valve. 1. gas pressure test connection at the valve outlet, in front of the burner; 2. maximum gas flow rate adjustment nut; 3. minimum gas flow rate adjustment screw; 4. adjustment device cover; 5. gas pressure test connection at the valve inlet, in the gas network.

Producers of two-circuit gas boilers of many brands set the boilers with a gas valve Italian company SIT. The adjustment of the maximum and minimum boiler burner output is performed by turning the adjustment screws located on the valve body.

Adjust the gas pressure in front of the burner in DHW mode:

On the boiler display it is obligatory to set the temperature of hot water to 60 o C. (to set the D.H.W. temperature, see above).

Remove the cover of the adjuster (pos.4 in the figure).

Turn on the boiler in domestic hot water mode by opening the hot water valve at full flow with the maximum water flow rate.

Adjust (decrease) the gas pressure in front of the burner

by means of the screw for maximal gas flow regulation

(pos.2). When rotating to the right, the gas supply increases,

and by turning it to the left it decreases. Visually observe the flame height in the boiler burner. The purpose of the adjustment is to reduce the gas supply to the burner so that the burner operates continuously and the temperature of hot water from the tap remains constant and comfortable.

We control the gas pressure in the network

The gas pressure in the gas network can drop below the pressure admissible for the operation of the boiler. It is necessary to check the pressure periodically, especially in frosty weather, when the gas consumption in the network is maximal.

Static pressure and dynamic pressure are measured at the boiler inlet. Static pressure is when the boiler does not use gas. Dynamic pressure is measured at the maximum gas flow of the boiler.

To measure the pressure in the gas network, at the gas valve inlet, connect the pressure gauge pos.5 U-tube pressure gauge. To measure the dynamic pressure, open the hot water valve all the way.

Normal dynamic gas pressure at the gas valve inlet must be between 1.3. 2.5 kPa (13. 25 mbar or 132. 255 mm. water. line.). If the dynamic pressure value is not within this range, contact the gas supply company.

See how to measure the gas pressure at the inlet and regulate the minimum and maximum gas pressure at the outlet of the SIT gas valve in this video.

The tap in DHW mode is eliminated by reducing the maximum pressure. To check the water tightness turn the adjusting nut anticlockwise.

U-shaped pressure gauge

A simple pressure gauge for measuring on a gas valve can be made from a transparent plastic tube by filling it with water and bending it into a U-shape. Push one end of the tube on the valve nipple and leave the other end open. Use a ruler to measure the difference of water levels in the branches of the tube. The measured distance is the pressure in millimeters of water column (mm).of the

Push a tube with an inner diameter of 8 mm tightly over the test connection of the gas valve. For other tubing sizes, you must use an adapter.

After completing the measurement, do not forget to carefully tighten the stop screw on the measuring connection and check its tightness.

Gas-fired boilers are the optimal solution for heating almost any room. They are easy to use, small in size and have a long service life, so they are equally suitable for both private homes and apartments.

Any gas boiler has 3 main components:

Depending on the model, the boiler may have various additional equipment, such as a pump, fan, expansion tank, safety valve, electronic control system, diagnostics and protection. If the boiler has such additional elements, it can be quite considered a miniboiler, which operates fully automatically. It independently maintains the temperature set by the program, controls all internal processes, and in case of an accident it cuts off the gas supply and shuts down.

The principle of boiler operation

To understand how a gas heating boiler works, you need not only to know its device, but also to understand what programs and functions are laid in it. In its work, the boiler is guided by the readings of the sensors. Using built-in electronics, it detects the need for hot water and triggers the control gas valve. After that the gas burner, which heats the water in the heat exchanger to a certain temperature, and the circulating pump, which immediately distributes it through the heating system is turned on. After the temperature in the system reaches a predetermined value, the boiler turns off the burner and goes into standby mode. When the temperature in the heating system decreases to a certain value, the boiler turns on the burner again and the cycle repeats.

All single-circuit boilers in heating mode work according to this scheme. Double-circuit boilers perform exactly the same cycle, but its work can be interrupted by the hot water system (DHW). Two-circuit boiler has a more complex water treatment system, since it performs two functions at once:

In addition to the main heat exchanger it has a second circuit (rapid heat exchanger), which is designed for the preparation of hot water. Two-circuit boiler can operate in 2 modes:

If the boiler operates in winter mode, the water is heated in the primary heat exchanger and distributed by the circulation pump through the heating system. When you open the hot water tap in the boiler is triggered by the flow sensor. It sends a signal to the control board, which switches the three-way valve from heating to DHW mode. As a result, hot water from the main heat exchanger does not go to the batteries, and remains in the boiler.

It begins to circulate in a circle, passing through a secondary heat exchanger and heating water for DHW.

The secondary heat exchanger is lamellar, so the water is heated almost instantly, and we instantly get hot water in the tap. This is until the hot water tap closes. After the water is shut off, the flow sensor informs the circuit board and it switches the three-way valve back to its original position and the heated water from the primary heat exchanger flows back into the heating system.

From the description it is clear that the principle of operation of the gas boiler does not allow for simultaneous operation of the heating and hot water supply. However, there are already special heat exchangers, which can do this (they will be described below).

The device of a gas boiler

Boilers of different manufacturers may differ in device and arrangement of elements, but they all have a typical scheme. We will consider it on the example of a two-circuit boiler (as the most complex).

  • gas valve for fuel supply to the burner;
  • gas burner;
  • ignition unit;
  • ignition electrode;
  • flame control sensor;
  • gas combustion chamber;
  • The primary (main) heat exchanger;
  • fan;
  • Exhaust gas draught sensor. manostat;
  • sensor of water temperature in the primary circuit
  • emergency sensor of primary circuit water temperature;
  • expansion tank;
  • circulation pump of the primary circuit;
  • filter of the heating system;
  • Water pressure gauge in the heating system;
  • water make-up tap of the heating system;
  • safety valve of the heating system;
  • three-way valve;
  • hot water heat exchanger (DHW);
  • bypass;
  • D.H.W.W. flow sensor;
  • D.H.W.W. filter;
  • water drain valve;
  • electronic control unit (control board);
  • regulators of heating and DHW system temperature;
  • switch of operation modes (summer, winter).

As can be seen from the large number of various sensors, half of the devices monitors the system and allows the boiler to operate safely in automatic mode. In addition, the boiler has standard fittings for:

  • fuel supply to the gas valve;
  • water supply to the heating system;
  • return water inlet from the heating system;
  • inputs of cold water for DHW;
  • DHW heating water outlet.

To more clearly understand the work of the boiler we need to consider each component individually and determine its function and purpose. It is worth immediately remembering that “unnecessary” and “unimportant” parts in the boiler does not exist, and a failure, even one of them will lead to a breakdown or malfunction of the boiler. Below we will examine in detail the most important blocks of the gas boiler, and what elements it includes.

Gas burner and smoke evacuation system

The main element of the gas boiler is the burner. In modern boilers, it is modulating, which means it is able to change the amount of gas consumed. This function at ignition and at the beginning of the heating cycle reduces the gas supply (heating the heat exchanger gradually). Then it increases the gas supply when approaching the set temperature and maintains it. When the water is hot and the time of switching off is approaching, less gas is fed. This reduces gas consumption by up to 15% and reduces the number of on/off cycles, increasing the life span of the boiler.

Preparation and supply of fuel is carried out by means of a gas valve. During operation, the fuel supply is regulated by a stepper motor. It is controlled by the microprocessor electronic board according to a program that is stored in the factory. Thus, using the standard control panel, you can set the desired temperature of the heating system and DHW.

There is also an ignition electrode and a flame detection sensor on the burner. Burner is in a closed combustion chamber, which ends with the exhaust. At the outlet there is a fan for forced smoke evacuation. In front of the fan there is a draught sensor. monostat, which will immediately shut down the boiler if the smoke is not drawn out. The manostat is activated particularly often in severely cold weather, when condensation freezes in the exhaust pipe and the exhaust gas outlet is blocked.

Heat exchangers

Heat exchangers are divided into two types: primary and secondary. The first is installed above the burner, as it heats the water of the first (heating) circuit. It represents a set of copper tubes in which water circulates by means of a flow pump. To increase the usable area and to quickly heat the water the copper plates (fins) are pressed on the tubes.

The secondary heat exchanger is needed for heating DHW. It has distinctive features that allow you to heat water instantly. The exchanger looks like a set of plates, between which the water circulates separately from the primary and secondary circuit. When the hot water tap is opened, the water in the primary circuit is not fed to the heating system, but is redirected to the secondary heat exchanger. Thus, instead of heating the radiators, the DHW water is heated. The peculiarity of a two-circuit boiler is that heating and DHW heating cannot be performed simultaneously. At home, it is practically not noticeable, since the consumption of hot water is insignificant compared to the operation of the heating system.

When the daily flow of water is large and competes with the heating system, a two-circuit boiler with a bithermal heat exchanger is used. They are characterized by the fact that they have only one heat exchanger, which is located above the burner. Its design is a bit more complicated, and inside the tubes of the main circuit are the tubes of the DHW circuit. It turns out that the burner heats only one heat exchanger, which simultaneously contains the water of the heating system and DHW (that is why it is called bi-thermal).

DHW system

The main difference between two-circuit boilers is the hot water system (DHW). It allows you to almost instantly get hot water. For this purpose the boiler has a secondary DHW circuit, which consists of a plate heat exchanger, water flow sensor and three-way valve. The main sensor that controls the process of starting the secondary circuit is the flow sensor. When you open the tap it sends a command to the control board, and that, in turn, to the three-way valve, which closes the water supply to the heating system and directs it to the DHW plate heat exchanger. As a result the hot water, heated in the main heat exchanger, with the help of a pump begins to circulate in a “small” circle inside the boiler, passing through a DHW heat exchanger and heating water in it.


It connects the flow and return of the main circuit. There is an adjustable bypass valve installed on the bypass, which opens in the event of critical pressure, and part of the water flows from the direct pipeline into the return pipe. The valve ensures the absence of water hammer when the pump is turned on and limits the maximum speed of water circulation in the heating system.

Expansion tank

When heated, the water begins to expand in the heating system and to compensate for the excess pressure, expansion tanks are installed. They are available for all boilers without exception, but may differ in shape and size (depending on the capacity of the boiler).

The expansion vessel consists of three parts:

During the operation of the heating system due to the membrane the tank equalizes the pressure changes, so during the operation of the boiler pressure remains unchanged.

Control board and sensors

Whatever the device of the gas boiler, it necessarily has a board (block) control. It allows you to set the necessary modes of the boiler, monitors and analyzes information from the sensors, performing automatic control of all processes in the system. On the board itself, there are no adjustments and settings, all settings are made in the factory. The only thing the user can change is to connect an external temperature sensor. If there is no sensor, the control system is guided by the temperature of water in the system and starts the boiler when it cools down.

If you connect a sensor, the boiler control system begins to focus on it. To connect the outdoor thermometer, remove the jumper on the board and connect the wires of the control device instead. There are simple membrane sensors, which only set the maximum and minimum temperature in the room. There are more complex electronic sensors, which can indicate not only the temperature but also the time of switching on and off the boiler. For example, the boiler will not work while you are at work, and will turn on an hour before your return.

Normal operation of the boiler, its reliability depends on a variety of sensors and control systems such as

  • gas pressure sensor in the system;
  • flame control sensor;
  • Exhaust gas draught sensor;
  • sensor of water temperature in the primary circuit;
  • Emergency sensor of water temperature of the primary circuit;
  • sensor of water pressure in the heating system;
  • the safety valve of the heating system;
  • sensor of DHW flow.

Thanks to them, the boiler can operate independently for a whole season without stopping and breakdowns.

Unfortunately, problems occur during operation that are not related to the boiler itself, but are caused by external factors. For example, if the gas is disconnected in the house, the boiler will instantly detect it and shut down. It will have to be restarted manually by performing special commands.

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If there are any errors or accidents in the boiler operation, it immediately stops working and gives the conditional signal. In models with an electronic monitor the error code is displayed in the form of a set of numbers or letters. In devices with analog (mechanical) control an error is indicated by blinking of indicators.

In the passport of any boiler there is a table with error codes, their decoding and instructions how to reset (remove) the problem. It is easy to find such tables on the Internet, the more so that error codes of almost all boilers are the same.

What to do if the gas boiler is broken and the hot water does not turn on? Instructions for diagnostics and repair

Installation of a two-circuit gas boiler can effectively solve the problem of hot water supply. But what to do if the hot water does not turn on in a gas boiler? Do not panic and call immediately to the emergency service or service center.

We will get acquainted with a principle of work of two-contour boiler, we will tell about the reasons which can lead to the termination of giving of hot water and ways of elimination of the arisen problems.

Understanding the nature of the equipment, you can not only independently identify the causes of failure, but also to eliminate most of the faults and restore the supply of hot water in full.

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