The cause of pressure drop in the two-circuit boiler


This manufacturer has a bypass element, which allows you to solve the problem of how to raise the pressure in the boiler Ariston in case of power outage.

cause, pressure, drop, two-circuit

It allows you to reduce excessive heating of the heat exchanger due to insufficient water flow. The flow of the heating medium in the system is started bypassing the circulation pump.


The minimum pressure at these boilers half a bar, in case of its insufficiency on the boiler screen displays errors E40 and E41. It can be adjusted with a tire pump because the valve on Baxi boilers is an ordinary car nipple.

Please note! At the first start of the coolant in the system, the boiler may display error E10, it passes automatically.


These Korean boilers are designed for a pressure drop of up to 0.1 bar, which minimizes the emergency shutdowns. Such units are ideal for high-rise buildings. The boiler is equipped with a system of nozzles, safety systems and devices that allow it to operate at a reduced pressure up to 4 mbar. The pressure can be adjusted by remote control.

At the first start, air gradually escapes from the system. That’s why the pressure in the heating system is dropping. Initially, it comes out of the boilers themselves. And since there are automatic air vents on the boilers and inside the boilers, usually on the walls, the air comes out of the boilers itself.

Plus, when you start a wall mounted boiler, there is a screw on its pump that serves to vent right in the middle of the pump. If you unscrew it, the air comes out first. Then there’s a thin trickle of water. After that the screw should be slightly clamped, usually it is on a rubber band, and then the wall boiler will not contain air and will be able to function normally.

Often at the first start-up the pressure in the heating system of water underfloor heating drops a lot. Huge floors can be as big as a hundred or two hundred square feet. There are long pipes underneath that initially have air in them. And then they’re filled with heat transfer fluid. So when you start the floor heating circulation pump, then immediately begin to hiss automatic air vents, which are on the manifold of the floor heating. Т.е. that coolant that starts to circulate through the water heated floor, it begins to push this air into the manifold. And as a result the air starts to come out of the air vents intensively, especially at the beginning. This causes the pressure in the heating system to drop.

It is necessary to monitor the pressure on the safety group and the manometer of the wall boiler, and if necessary to make up for it. Air can escape from the boiler coil. It can also burst on the automatic air vent. And possibly to the radiators of the other floors. It will accumulate in the radiators, so they must have the Maevsky cocks. If you see that the radiator has stopped heating, open the Mayevsky valve. First the air hisses as well, then water flows in a thin stream. This means that the air is completely out.

After the start of operation for another week or two, maybe even longer, it is possible air from the water underfloor heating. Accordingly the pressure in the heating system will drop. This should not scare you, because over time, the intensity will decline and after a few weeks almost ceases.

Causes of pressure drop

The pressure in the gas boiler can drop, at:

  • leaks from the heating system;
  • Failures in the power supply;
  • defects in the expansion tank;
  • Improper operation of the equipment or poor quality installation.

In case of drop in working pressure the boiler stops working: water stops flowing into the heat exchanger, so the automatic system stops the equipment. Below we will consider in detail the most common causes and tell you how you can fix them.

Pressure drops when you turn on the hot water

The most common problem. If at disconnection of hot water pressure is quickly restored, it means that the problem with the make-up tap: it is either not closed or faulty. In this case the pressure between the heating circuit and the water system is equalized, but as soon as you open the tap it drops sharply.

Such a malfunction is dangerous not only a violation of the work, but also leads to increased oxidation of the pipes, the emergence of precipitation of salts and complete clogging.

In addition, there may be a faulty air supply to the heating circuit or malfunction of the 3-way valve.

Water leakage

If during the operation of the boiler is constantly low pressure, the possible leakage of water in the connecting nodes, radiators or the expansion tank. In this case it is necessary to check the entire heating system for leaks, even if the water is not dripping from a closed boiler.

To avoid problems, before the heating season conduct regular maintenance: specialists will check the entire system for leaks, as well as replace worn gaskets and seals.

Air clogging

Cracks and leaks can lead not only to leaks but also to air being sucked into the heating system, which causes air bubbles. To spikes in pressure can also lead to incorrect filling of the circuit water or its high temperature (more than 85 degrees).

Determining the presence of air plugs is quite simple: if in any part of the system the pipes are cold, most likely an air plug has formed there.

The problem can also be easily solved. Simply bleed excess air through special bleed valves.

Defects of the expansion tank

The expansion vessel performs two functions in the system: it stores excess water when heated and also balances out pressure changes.

The tank consists of two compartments (with air and water), which are separated by a membrane. As the water heats up, it expands, putting more pressure on the diaphragm, compressing the air. When installing the tank air is pumped into it through the nipple from above. If it has been in operation for a long time it can start to leak air, so that the diaphragm is no longer pressurized.

Boiler Keeps Losing Pressure

In this case, the only solution would be a complete replacement of the tank, to replace only the nipple is impossible. But before that, be sure to check the tightness of all other parts of the system. maybe the problem is in them.

Cracks in the boiler heat exchanger

During operation, microcracks occur in the heat exchangers, which begin to leak water and also suck air inside the system. Detecting this fault is quite problematic: the water inside the boiler evaporates very quickly. The problem can only be solved by welding cracks or complete replacement of the heat exchanger.

Malfunction of measuring instruments

If the pressure gauge shows low pressure, but the boiler is still working efficiently, there are no leaks or cracks anywhere, and all system components are serviceable, then the control device itself may be defective.

You can check this by installing an additional pressure gauge on the boiler inlet. Replace the faulty unit.

The problem with the drain cock

A pressure relief valve (or bleed valve) is mounted separately and is needed to balance the pressure in the heating system. The spring presses on the plug, as soon as the pressure exceeds the norm, the spring compresses, opening the plug and releasing either air or water.

After 7 cycles, the spring wears out and ceases to fulfil its function: the pressure either jumps or constantly decreases. In addition, there will be a constant leakage.

Try to turn the valve. If the problem persists, then the mechanism must be replaced: it is not advisable to repair the valve.

Low pressure or pressure spikes in a new gas boiler

Pressure surges during the initial start-up of new equipment are quite normal: there is still a lot of air in the circuit, which will escape with the help of drain valves and the pressure will normalize.

Why does the pressure in the system increase??

Too much overpressure in a boiler can be caused by two things:

Water is an excellent solvent and not only contains mineral salts but also gases such as nitrogen, oxygen and carbon dioxide. Their solubility decreases as the temperature rises. Gases bubble up out of the fluid and into the system. Most of them are removed through the automatic air vent, but sometimes they pass into the radiators. An air lock obstructs the circulation of the heat transfer fluid, which increases the pressure in the boiler. One of the most frequent causes of “air s” is that the filling rate of the system is too high.

To detect an air lock, just compare the temperature at the top and bottom of the heater. You don’t need a thermometer for this, you can feel the difference with your hand. To remove air s from radiators Maevsky cocks or other designs air vents are installed on them. After several cycles of heating and cooling of the coolant air release will stop.

The pressure in a two circuit boiler is rising

finding the stop valve (valve or gate) in the closed state;

Contamination of the filter (a preventive measure is the regularity (3-4 times in 12 months) of filter cleaning);

Failure of an automatically executed boiler function;

makeup valve leakage.

One of the main regulating devices is the aforementioned regulating valve, which has symbols indicating the rotating direction of opening and closing. Because of the importance of this device, it is preferable and more rational to begin the inspection with determining the condition of this part.

Why is the pressure in a dual-circuit gas boiler growing?

The value equal to 1-2 bar is attributed to the value of the norm. At 0.6 bar (minimum), no solenoid valve starts, and at 3 bar (maximum), the liquid is discharged. Practitioners in the field of maintenance identified a factor that increases the pressure in the gas boiler:

Breakdown of the impregnation valve;

secondary heat exchanger dysfunction.

The summary of recorded statistical data, some informal data of forums, as well as user feedback informs about the predominant prevalence of the first of the above factors. Why the pressure rises in the heating boilerMaintenance practices have established a set of external defects in the boiler, affecting the norm in question:

damage to the walls of the heat exchanger (cracks due to factory defect, low strength, water hammer, depreciation);

make-up valve is not closed;

Decrease of the pipeline pressure;

The three-way valve must be replaced;

there is no movement of the pressure gauge pointer.

The formation of one or more of these faults requires professional intervention and the call of a heating engineer. You should take into account the ability of heating equipment to explode and follow the rules of technical operation.The pressure in the heating system of the wall boiler grows The development of the emergency situation occurs according to one of two schemes. When the problem lies in the function of the make-up valve, the pressure in the heating system of the wall boiler is growing slowly and cyclically (a precursor to the risk of untimely detection and flooding of the room). Fistula formation (fistula, crack or through hole) at the location of the secondary heat exchanger heating and water pipes. the second, but not so common, variant. Causes of pressure growth in the gas boiler A generalized review of the operating period of popular models and their configurations (electric and boilers operating on gas, diesel or solid fuel) indicates the following significant causes:

errors in automatic functions;

loosening of pump impeller fixation (looseness);

Defect in the secondary heat exchanger baffle, accompanied by liquid leakage.

To prevent the consequences of an emergency situation it is desirable to regularly monitor the gauge marks (keeping a household log) and the frequency of drainage (the availability of this information speeds up the solution of problems, it is useful in case you ask for help from a heating engineer).Why does the pressure in the boiler constantly rises When the pressure in the boiler continuously rises, it is recommended to check the make-up valves, bleed air, inspect the tube expansion tank for clogging. Why pressure in the boiler is falling, then risesLack of stability, accompanied by spontaneous decline and rise, develops with the filing of a dense accumulation of air in the cavity of the radiators, wear or defects spool and loss of sealing properties of the membrane expansion tank, responsible for compensatory processes. Damage is indicated by an increase in pressure, the value of which is indicated by the manometer or safety valve (emergence of a leak):

Leakage of the heat exchanger has been reduced by multiple cracks;

Operation of the equipment with an open make-up valve;

defect in three-way valve;

The manometer is defective.

Allowance for operation is safe when the valve is closed;. Filling of the circuit from above;. Filling of the circuit from the top. Loss of function of the listed parts requires their disassembly, purchase of new ones and their installation. Air lock as a reason of pressure increase in closed systemsTight accumulation of air, obstructing liquid movement, forms the basis of pressure drop. Creation of air s is preceded by:

filling the circuit from above;

exceeding the fill flow rate;

Failure to bleed air from radiators;

Pump impeller looseness.

Why the pressure increases in the closed boilersThe pressure in the closed boiler is increased by sealing the accumulated air. Negative effects are amplified by multiplicity. Deviations from the established norms of the starting procedure contribute to the emergence of.Causes of pressure increase through air s in an open system Filling the cavities in the system with the heat transfer medium errors made during start-up or after finishing adjustment work are the reason for the dense air accumulation (s).Why the pressure in the boiler must be monitoredElevated pressure is a generator of excessive loads that irrationally increase the cushioning. Overloaded functioning is fraught with destruction of equipment and accidents, considerable expenditure of money. Normalization works belong to the category of immediate measures and problems in finding the analogous spare parts. Thus, systematically observe dynamic, static and maximum levels. Why does the pressure rise in closed systemsIn addition to defects, wear and tear of the Maevsky valve designed to release air accumulated in the radiators (opens with a special key), the factor is a group of

filling of the heating circuit from above;

start-up happened with a significant acceleration of the heating medium filling;

looseness of the pump fan conducting the air;

Defective air vent.

Failure to bleed the air in time after a repair leads to an increase in the temperature of the medium in the boiling water system.Cause of high pressure in open systemsDense air s, otherwise known as s, are a common occurrence. Their formation is caused by errors in the sequence of filling the circuit. The solution to the situation is a smooth release of air by opening the safety valves located on the radiators (radiators). How to check the pressure in the boiler and the circuitCheck the pressure by means of instruments equipped with a dial on the spigot as well as near the manifold. Initial parameters are set during initial start-up. The pressure gauge must be checked weekly and a record of the gauge is recommended. Prevention of increased pressure in the system Increases the service life of a set of preventive measures to prevent the scale of the accident and reduce the risk:

a safety device (pressure gauge, air vent, safety valve); a corrosion inhibitor as well as a scale inhibitor (used by adding it to the coolant); an expansion tank to compensate for fluid build up during heating.

Compliance with the first of these requirements is mandatory in the operation of the floor type (wall-mounted boilers are equipped by default). What should be the pressure in the heating system The norm of the value is set at a level below 2.5 bar, but not decreasing to a level below 1 bar. Causes of pressure growth ways of solving the problem The source, provoking the growth, experts determine the dysfunction of the expansion tank:

Loss of integrity of the membrane causes filling of the tank with coolant (requires replacement of the tank or the membrane); mismatch of the pressure head (balance is restored by draining the water, blocking and pumping by the mechanical pump valve); water hammer (violation of the sequence of installation).

Pressure increase due to the expansion tank Operational standard pressure of the tank is set at 1.5 bar. Two parts are subject to inspection: the diaphragm and the spool. Air is pumped using a slide valve. When the part leaks, there is a simultaneous decrease in the head of the tank and a pressure surge of the boiler system. Compensating function is performed by a membrane, which is a flexible plate (skin). The tightness of the fitting is checked by opening the valve. Increase of pressure in the heating circuit Irregular filling of the circuit, low temperature and stopped flow of the heating medium cause the value of the heating circuit to increase. Signs are established by a step-by-step inspection: the make-up valve for signs of worn gaskets, performance and deformation of parts, the presence of scale forming a leakage development; the presence (absence) of air accumulation.Elimination of detected deviations is carried out by restarting the system.How the operation of the pressure accumulator affects the pressure The smooth operation of the expansion vessel determines the normality of the pressure value of the circuit. A prerequisite for circulation deviations is impermissible errors in the calculated volume of the expansion chamber and the installation of the air chamber, as well as damage to the membrane integrity.

Pressure drop Below the norm Drainage results in automatic shutdown of a number of equipment. The fundamental factor is water leakage. Reduced fluid volume of the heating system is characterized by the feature of unnoticeable leakage. No heavy flooding. Water comes out in droplets that evaporate instantly. Checking the pressure in the air chamber and pumping up the air is permitted under the following prerequisites:1. no coolant fluid;2. Chamber pressure is 0.5 bar higher than its limit in the system.The scheme of debugging works is as follows: 1. closing of shut-off valve;2. Drainage of water through the drainage outlet;3. check the pressure;4. pumping up or down to the required level;5. Filling the circuit with cold water;6. venting, carried out until the simultaneous lowering of the circuit and tank head.If you feel unprepared to work on your own, when the need arises for the first time, it is advisable to start setting the parameters together with a person who is familiar with this situation.Gas double boiler does not hold the make-up tapThe item is usually located at the bottom, in the vicinity of the cold water inlet. Failure develops two factors: sealing rubber of a rod has lost elasticity; rupture of sealing rubber.Preventive measures are to change the rubber band, as well as the correct way to tighten the faucet.As a conclusion on the outcome of the reasons considered unambiguous is the fact of regular maintenance, which one way or another will have to perform yourself, or to entrust it to a specialist (the decision is advisable to be guided by your own knowledge, availability of free time). It should be borne in mind that the stability and sufficiency of the heating of the dwelling depends on the correct function of the boiler system. This is the purpose for which these products are purchased.

Features of a boiler Navien

In these units, the problem, most often, lies in the leaks, especially when using liquids with high m glycol. Antifreeze is very fluid, so it penetrates the smallest cracks. Sometimes they are not easy to find, so it is recommended to invite a specialist who will thoroughly check all the strapping. Detected leaks must be corrected, then refill the expansion tank and clean the pipes of air.

And also the pressure slightly decreases as the coolant. Usually, after turning on the boiler this problem is solved by itself. If the fluctuations are significant, a diagnosis is required. The latter can result in repair or replacement of the equipment.


To fix it, it is enough to perform the actions similar to those described above. In rare cases, if the problem cannot be solved, you will have to purchase and install a new heating device.

Wall mounted gas boiler Deluxe 13A model, open combustion chamber, manufacturer. Navien, South Korea.

Serious problem or temporary inconvenience? Why is the pressure in the heating system falling, is it dangerous?

No heating system in your home or apartment can function without sufficient pressure.

Its sudden changes have a negative impact on the state of the entire system and heating equipment, leading to breakdowns and creating emergencies.

Is Your Central Heating System Losing Pressure?

These are the reasons why low pressure has to be found out and eliminated.

Norm and Control

The process of operation after some time can give the boiler malfunctions. It occurs under the influence of a negative impact on the heating system. Such a negative effect can be called both excessively high and low pressure, measured in atmospheres. The normal level is 1,5-2 atmospheres. And why the pressure drops in the gas boiler?

If we talk about private households, then here, as a rule, are used autonomous heating systems with power from single-circuit and two-circuit boilers. Two-circuit boilers are particularly widespread. In addition to heating, such units provide water heating. One circuit in them heats the heating medium circulating through the pipes, and the other provides the operation of the hot water system.

What to do if the pressure in the gas boiler drops?

A fairly common problem when using two-circuit gas boilers, when the hot water is turned on, and the pressure inside the boiler begins to drop sharply. The pressure drop is almost to zero, and warm water has a pungent smell. Sometimes it even happens that due to the error of reducing the pressure the heating boiler automatically shuts down. Another case of pressure drop is observed when the water supply is temporarily cut off in the house, after which the boiler fuses do not allow it to restart. If you try to turn it on, the tank will give an error about pressure problems, and simply will not turn on. In general, the drop in pressure in the boiler is very bad for the boiler and water supply systems, so you need to immediately diagnose the problem and then proceed immediately to solve it. What is the problem and what you need to do, read below.

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