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There is no draft in the chimney of the gas boiler

To understand what is the draft in the furnace chimney, how it is formed and what it depends on, you need to remember the laws of physics:

  • Warmer air has less weight and rises upward, cooler air is heavier, causing it to sink downward.
  • The gaseous substances move from the higher pressure area to the lower pressure area.
  • At the surface of the earth the pressure is higher, the higher up, the lower the pressure.

On the basis of these laws and arranged chimney draught in heating boilers and furnaces: due to the difference in pressure / temperature, the smoke and combustion products through the chimney are removed outside the room. In normal operation, the smoke moves from the bottom up through the chimney leaving the room.

So, what is the draft in the chimney: it is the movement of air through the chimney from a lower point (indoors) to a higher point (outdoors over the roof). In essence, the air is pulled from the furnace/boiler to a lower pressure area (at 5 meters above the boiler, the pressure is noticeably lower). Hence the popular name of this phenomenon. draught.

During normal operation of the boiler or furnace the smoke escapes into the chimney. At the initial stage, while the furnace is not yet heated and the fuel is not burning, the air goes to the chimney due to the pressure difference, which is formed by the height of the pipe. Later on, when the temperature rises in the furnace, the air warms up and becomes lighter, the speed of the gas flow through the pipe increases. The draught works fine.

But the draught in the chimney is, if there is an inflow of fresh air in the room due to ventilation holes or cracks in the windows. If sealed glazing is installed, no air inlets/vent grilles leading to the outside (or at least to a room with air supply), there will be no draft. No air movement and everything does not work. Smoke escapes poorly/badly or at all goes into the furnace room. Just no draft in the chimney no air movement from the bottom up. The solution to the problem to make air inlets and everything should work. In general, there are many reasons why the draft is absent, but this is one of the main.

How to increase the draught through the boiler, what to use. the deflector, the smoke pump or.

Sometimes the draft through the chimney is not enough, the fuel does not want to burn intensively, blowing in the wind, smoke is released into the room when you open the flaps, why this happens and what you need to do to improve the draft, can be put the smoke pump?

Why there is no draft

Natural draught depends on pressure differences in the chimney. And the pressure depends largely on the temperature difference between air and gases, or rather the difference in their densities In winter, when there is frost outside and the room is warm, the air rushes well into any elevated chimney, the boiler heats without problems. When the furnace is hot and the frost is still good, the draft is usually bearable, even in the most poorly constructed systems. In the off-season, too, the draught is usually satisfactory.

But in summer in the heat, to heat the stove or a usual boiler on a natural draught can be problematic. Initial draught can be even reversed. The room is filled with smoke, stable combustion is not achieved, what to do?

Also, the natural draught can be significantly affected by the following reasons.

  • The chimney is sooty and clogged.
  • Other chimney overlaps. collapsed plaster, compression by structures, bulging and scuffing of corroded burnt casings.
  • A hole formed in the chimney. suction in addition to the furnace of the boiler.
  • The chimney is set too low. lower than laid down by SNIP.
  • Insufficient cross-sectional chimney installed, less than boiler manual for given combustion power, too high aerodynamic resistance.
  • The boiler, the furnace with too much aerodynamic resistance inside, with a complex system of flue ducts around the heat exchanger is installed.
  • Air supply dampers, ash-pan lids, etc. are closed.п.
  • The chimney is closed, the draught regulator, the gate at the gas exhaust, at the place of connection of the chimney to the equipment is blocked.
  • No free air flow into the room, it is hermetically sealed, during combustion creates vacuum in the furnace, the draught stops.

As you can see, if the draught is disturbed, then you must first check the serviceability of the equipment, the correct adjustment of air supply, the position of the dampers, and be sure to clean the chimney from soot. How to clean a chimney. recommendations

Water heater draft testing

  • But for many people it is important:. how to melt the boiler in the summer, for example, to heat water.
  • Also, many are aware of the “diseases” of their boiler-chimney system, but there is a desire to increase the draft on the existing equipment. how to do?

Installing a deflector. helps increase the draft

Deflector. a device on top of the chimney, which creates an additional vacuum in it due to the wind. The disadvantages of this method of increasing the draft:

  • If there is no wind, there is no increase in draft, too obvious disadvantage.
  • There is another hard-to-reach unit, which needs to be cleaned from soot, giving the opposite effect when dirty, inhibiting the draft.
  • Also, the method is characterized by a slight increase in the draft, only 20-25% if there is wind at high chimneys.

Is it worth it or is it enough to install a normal rain umbrella? In addition, the unstable draught force is not the best situation, below we will consider why

Nevertheless, you can make a deflector yourself from stainless steel, according to the given drawings.

How to make a deflector FAGI. scheme for making.

How to make a cone for a baffle

Drawings for making Wolpert-Grigorovich deflector.

Install a chimney pump to increase the draft

There are electric ventilation systems for increasing the draft in chimneys. Large boilers are equipped with them according to the projects from the beginning. For boilers such equipment can be installed additionally on standard pipe diameters.

  • There are draft enhancers installed at the end of the chimney in the form of a propeller fan. But this option is unpopular because of the complexity of installation at a height and the subsequent cleaning there, especially if tarry wood is used.
  • Another version of the chimney. of the centrifugal type, installed at the outlet of the boiler in the hot gas zone. Usually there is a separate bypass of the chimney blocked by a damper, so that with natural draught the gases do not go through the fan.

This device creates at work powerful fixed draught which will blow practically any system, if there was an access of free air in a furnace (in a premise) and will not pay attention to blowing off by wind, for example But this system has very significant lacks.

  • A stable draught and large quantities of fuel are produced during operation. In case of power failure the draught is lost, then a large quantity of carbon monoxide can be released into the room. This is extremely dangerous. Such a smoke exhauster must operate in a complex automation with other devices of the boiler room, or for short periods of time under constant human control.
  • Impeller gets dirty too quickly, needs regular cleaning, so it is not practical.
  • Obstacles are created for realization of slow continuous combustion.

Ways to increase the draft

If the chimney creates insufficient draft, it is necessary to replace it, install sandwich pipes of appropriate diameter for a given capacity of heating equipment (according to the instructions, according to the tables), and the height according to the requirements of SNIP (half a meter above the ridge when placing the pipe near him and t.д.).

If you need summer furnaces, you can equip the boiler with a centrifugal chimney pump for sure infrequent starts under the control of a responsible person in hot weather. But there is a simpler solution.

How to melt a boiler in summer or furnace after a long break? The folk method. to stick a vacuum cleaner by blowing into the ash tray, or any other fan to put on blowing for a couple of minutes, until it flares up. See video

No draft in the chimney stove: what to do, possible causes and fixes

Let’s consider in detail why there is no draft in the stove or chimney of a private house or bath, and what to do. Let’s find out how to identify the presence of this problem, and what to do to fix it.

Draught is the force of movement of flue gases through the exhaust duct, resulting from the difference in air temperature. If it is normal, the products of combustion freely go out into the street, if it is not enough (or it is not available), the gases accumulate in the tube and either clog the hose, gradually reducing its capacity, or go back into the room. This is dangerous because the smoke contains harmful substances that can be poisoned.

The following signs will tell you about the problems:

Back draft in the chimney of the gas boiler

In some cases there may be such a phenomenon as reverse draught. This is reflected in the fact that the gas flow does not go up through the pipe but goes back down into the room. Such a problem affects the domestic comfort, so it is necessary to get rid of it, so that the room has normal conditions for living. The draught is not always dependent on the quality of the chimney, this phenomenon can occur even if the best materials and devices were used. As the source may act and natural factors, so you need to understand what is the cause of back draft in the chimney of the gas boiler to find an appropriate way to fix the problem.

Common Wood Stove and Firplace Backdraft Smoke Issues

Gas boiler draft error

The most commonly used gas boilers for heating private homes. Many people choose them for the availability of fuel. In addition, most modern models are characterized by reliability, safety and long service life. For their manufacture use automatic systems and the highest quality materials. Although in the process of operation can cause various problems.

One of the most common faults is a lack of draught. This is normally indicated by a fault in the heating boiler. Failure can manifest itself as follows:

With such a malfunction encounter people in the house which installed a boiler air-air. The fact is that in floor units with an open burner the key role is given to the natural draught. It ensures the flow of air necessary for combustion into the chamber. It determines the intensity of combustion and efficiency of the boiler. For comparison, in heating equipment with a closed combustion chamber, the air supply is forced, so the problem occurs less often.

The main causes of poor draft in the chimney

Most often, problems with the draft arise from miscalculations made at the design stage of the chimney, because it is often done by people who do not have either special education or sufficient experience.

In addition, often the chimney clogging, strong air currents occurring in it, as well as various atmospheric factors leads to draft failure.

The first reason. mistakes in the chimney design. Poor draft in the chimney can be due to too low chimney, while with too high chimney, on the contrary, there is too strong draft. The optimum height is slightly more than 5 meters, in which case the draft should not be a problem. The chimney cross-sectional area, which must match the size of the furnace, is also of great importance. Thus, the combination of a narrow pipe with a powerful stove will result in a large volume of smoke not being able to escape properly and will begin to leak into the room. At a disproportionately large chimney all the heat generated by the combustion of fuel will literally fly into the chimney. Categorically not recommended in different areas to install pipes of different diameters, as this will inevitably lead not only to problems with the draft, but also to an excessively rapid formation of soot deposits. Soot accumulation, in turn, will reduce the diameter of the chimney, resulting in each time the process of lighting the furnace will be more difficult.

Also affects the strength of the draft and the shape of the chimney hole: with a round draft will be much better than with a square or rectangular. The thing is that in the corners, there are additional whirls, which create obstacles for the overall air flow, resulting in a general decrease in draft.

With regard to materials, the least common complaint about the lack of draft in the chimney will be those in whom it is made of brick, but in the presence of a metal chimney draft problems occur very often. The fact that the metal heats up quickly, but also cools down quickly, so that the cold air goes down.

Cause two. poor ventilation.Back draft in the chimney can be caused by a complete lack of ventilation in the room for the furnace, or, on the contrary, by strong drafts, which as if to confuse the smoke, which reverses its direction and begins to escape into the room.

Particular attention should be paid to the issue of ventilation and in the case if you use a gas boiler for heating. In the process, it will burn the air in the room, resulting in a serious lack of oxygen and the air will become very rarefied. Because of this a stream of air will periodically rush through the chimney, which will invariably lead to fading of the heater and the smoke in the room. The situation can be further complicated by having airtight plastic windows that do not let air in from the street. In such a situation, be sure to take care about proper ventilation.

The third reason. external factors. If you can not determine why there is a reverse draft in the chimney, pay attention to different atmospheric phenomena, it is possible that they are the cause of this trouble. Problems with the draft can be caused by, for example, high humidity or strong wind. A similar situation occurs when it is significantly warmer outside than inside the house (this often occurs in the springtime, in particular). In this case, you should simply open a window and ventilate the room well, allowing the temperature to equalize.

Trying to figure out why there is no draft in the chimney, you need to pay attention to the location of the chimney. It is best if it is placed in the interior of the building, in this case it will be less affected by various external factors. If the chimney is built from the outside of the house, then in the cold it will take longer to warm up, and the draft will be much worse. Also, condensation will often form in it.

The main causes of attenuation

If the equipment was working properly before, but now the automatic valve cuts off the gas supply, there can be several reasons. Depending on these will be different and ways to eliminate them.

The draught is reduced/lost

Rule of thumb for attenuation of atmospheric boilers: Check the draught. This can be done with a match or lighter, which should be brought to the inspection window.

Further steps depend on the behaviour of the flame:

It is important not to forget to close the gas tap properly. But that’s not all.

Remove the part of the pipe that is connected to the outlet spigot and check the draft now in the chimney:

What will actually have to be cleaned? Why is there dirt in the chimney?? It accumulates natural products of combustion in the form of carbon and soot deposits, fallen leaves, and sometimes even the boiler goes out because of a bird that has flown in!

If the clog formed at the inlet, to clean it is not difficult and yourself. And if at the top of the pipe. have to wait for the wizard with the tools (may have to use access from the roof).

Back draft in the chimney

Sometimes the boiler may go out due to back draft. This means that because the gas boiler is blown out by the wind, the smoke is not coming out of the chimney to the outside, but back into the furnace, thereby knocking out the flame.

The solution to the problem may be alternative:

  • Install a protective cap on the end of the chimney (popularly called a deflector, popularly called a “mushroom”).
  • Extend the chimney itself by 1-2 m, if the height and location of the nearest buildings cause a disturbance of air circulation.

Hoods cornice type are currently prohibited under SNIP II-35 and SNIP 02.04.05. But in some cases installing them may be the only solution. so it is better to consult your gas engineer.

The nozzle or the filter of the burner is clogged

If the igniter does not ignite when the boiler is switched on, this is a sure sign that the starter elements are clogged. It is necessary to clean the nozzles of the igniter nozzle, the fine mesh inlet filter or the filter of the kindling burner. You can do it yourself with handy tools.

For example filters. easy to blow (even just blow, but if you have a hand-held vacuum cleaner or pneumatic spray. will certainly be more convenient). With nozzles you will have to scrape with a thin copper wire from fouling until the original diameter of nozzles “returns”.

The pressure in the gas supply line has dropped

The turn off the burner is the first sign of drop in pressure in the gas supply line, while the flame of igniter does not extinct at the moment of stopping the boiler.

The first thing to do is to assess how the gas flows through the pipeline. To do this, unscrew the hose connections and open the valve completely, and then watch:

  • If it hisses strongly and produces the smell of methane, everything is normal with the supply;
  • If the signs are almost imperceptible or there are no signs, the problem is in the gas supply system.

After that, immediately close the cutoff valve, return the hose to its original position and check the tightness of joints with soapy water (if it foams at the joint, it is 100% leak).

If there is no leakage, deal with the meter: after repair there may be scale or rust in it, which will cause poor gas flow. A “clogged” flow meter shows incorrect data.

However, you can not clean the gas meter itself according to the decree 61-FZ. Only representatives of the gas service with the appropriate license should do this.

Not enough oxygen to burn gas

The cause of fading of the boiler can also be bad ventilation. Let’s try to understand what it means.

Lack of air is most often caused by the following prerequisites:

  • tightness of plastic windows;
  • Insulated, uninsulated interior doors;
  • Boiler room layout with irregularities;
  • Excessive exhaust in the kitchen;
  • Forced ventilation in the bathroom and toilet.

You can check the lack of oxygen by opening a window and turning on the gas burner. If the flames have stabilized, the situation is very clear.

there, draft, chimney, boiler

The problem is solved as follows: install air intake valves on the windows or organize a system of forced air intake from the street by installing an air intake valve in the wall.

Electrical circuit violations

Incorrect no-flame signals are being sent to the solenoid valve due to a breakdown in communication with the thermocouple. It causes the gas supply to stop.

When exactly the boiler goes out immediately after a short run or after selecting another mode, this is already a signal of problems in the electrical circuit:

  • Breakage of contacts of the thermostat, thermocouple or discharge sensor;
  • the thermocouple does not enter the flame zone or does not give the correct voltage;
  • Breakage of thermostat, solenoid coil or thermocouple.

All these problems can also be solved without calling a master. The main thing is to follow the algorithm.

In order not to lose the correct sequence of operations, do the following step by step:

  • check in turn the resistance on the sensors and connecting devices. 0.3-0.5 ohms is normal;
  • Clean all “oxidized” areas with fine sandpaper, tighten loose contacts;
  • disconnect the thermocouple from the main unit, connect the tester and, having pressed the start button, turn on the ignition burner;
  • Measure the voltage, normal value is 10-50 mV.

If everything is OK, put everything back, adjust the position of the thermocouple. If there is no voltage, remove the top cover of the main unit, warm the thermocouple with a ray, press the safety valve and then release.

Natural, Induced, Forced and Balanced Draft Explained!

If the valve is still holding, remove the unit with contacts and supply voltage (220V power) to the coil, bypassing the thermostat.

After these manipulations you can start the boiler. If the problem is not solved, it means that the old thermocouple and coil solenoid valve can not be repaired. We need new parts.

Causes of poor draft of the gas boiler

It happens that the chimney of a gas boiler with an open combustion chamber, there are problems with the draft, and the draft sensor of the gas boiler does not allow it to start. And like the diameter of the chimney chosen correctly, and the height of the chimney is sufficient, and the geometry of the flue duct and chimney is normal, and the draft no. The reasons for the loss of draught or it is difficult, there may be many.

This can happen for the following main reasons, provided it is not the gas boiler. Let’s look at some of them:

Debris in the chimney in the form of leaves falling into the chimney. It may be blocked by snow or the mouth may have frozen. This is especially true for chimneys with a difficult flue gas outlet due to a deflector, umbrella, or other overhang. Eliminate this is simple. clean the chimney or redo the end of the chimney so that the smoke comes out without delay. That is, to make sure that the flue gases from the boiler to the mouth of the chimney passed freely, and did not meet resistance.

Wind blowing can be prevented by installing a wind deflector or a wind vane on the chimney. There may be side effects from installation of these elements, see Fig. 3. point 1.

3) Insufficient supply ventilation.

It takes 10 m3 of air to burn 1 m3 of natural gas. Combustion requires oxygen, and if this is not available, the igniter and burner of the boiler goes out. Due to the lack of combustion air, there may be a reverse draft in the chimney duct by sucking air from the street through the chimney. Maybe in the same room as the boiler (eg kitchen, which is often the location of the gas boiler) may be working exhaust, which blows out the air (oxygen) is already missing. Although, forced exhaust ventilation without forced air supply is wrong. In addition, there may be plastic windows that obstruct the natural airflow. To solve the problem with a lack of oxygen for the normal combustion of gas in the boiler must organize a normal fresh air ventilation.

4) A poorly insulated chimney mounted along the façade.

Gas boiler works cyclically, on. off, on. off. Smoke gases in a poorly insulated chimney quickly cools, an “air lock” is formed, because the colder gas is denser than the warmer, and it prevents the movement of flue gases. Besides, an uninsulated flue causes significant condensation, which means intensive condensation on the inside wall and the risk of freezing (see Fig. 4). point 1 causes of bad chimney draught). Solve the problem by insulating the existing chimney, and the right way. better at the stage of selecting the chimney to provide for the installation of a well-insulated double-walled chimney factory-made. sandwich. And the more the layer of insulation, the better.

5) The chimney is in the area of wind overpressure.

The norms of the location of the chimney mouth relative to the roof ridge or the neighboring building, a tree. This can be solved individually: by increasing the height of the chimney, cutting off the interfering wood, etc.д., In general, the elimination of the overpressure zone at the chimney’s outlet.

6) Flame failure due to excessive draft.

You have opened the balcony, window, etc.д., There was a sudden change of pressure inside the room. To avoid this it is necessary to prevent such a phenomenon. And perhaps this cause can be combined with point 3 “Insufficient supply ventilation”. If the ventilation were done correctly, there would be no pressure differences in the room.

Here are briefly the main causes of draft problems in the chimney of the atmospheric gas boiler, because of which it can not work properly.

In addition to ignoring the cleaning of the chimney, which, incidentally, should be regular, resolution of other causes of poor draft should be provided at the design and construction phase of the chimney and boiler room. Of course, there may be individual, individual cases that do not fit into the listed, and then you need to invite a competent installer or specialist for its resolution of the problem formed.

The color and shape of the burner flame

The simplest, but not the most accurate visual method of checking the draft in the gas boiler. It is enough to look into the technical window of the boiler, located closer to the bottom of the boiler, burner module (on some models you will need to remove the facing panel).

If the color of the flame periodically changes to red, it indicates insufficient draft, the boiler does not have enough oxygen for complete combustion of gas. If the burner flame constantly changes shape and direction, you hear whirling sounds and drafts, there is a reverse draft, that is the movement of air masses in the opposite direction, caused by errors in the design of the chimney and wind gusts.

With a lit match

A more informative and proven method. To check the draft in the chimney of the gas boiler, bring a lighted match to the technical hole (window) of the boiler unit:

  • If the flame of a match tends visibly to the inside. the draught is present and most likely complies with the norm.
  • If the shape of the flame of the match remains unchanged. there is no draught and it is necessary to take measures.
  • If the flame turns to the side opposite to the boiler. there is a reverse draft.

The same principle can be checked with a thin sheet of paper.


Professional device for measuring the velocity of air masses, also called a wind meter. This is the most accurate and informative way to measure, but the cost of device starts from 2 thousand. Therefore it is expedient to use it only if it is possible to take it for temporary use.

The normal draught values should be from 10 to 20 Pa.

Boilers with a closed combustion chamber usually do not need to measure the draught. If there are any irregularities, combustion in them is simply not possible: the air flow is not carried out without a blower, the automation always reports problems in its operation.



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