Let's analyze the situation when water boils in a heating boiler, and it turns off in emergency mode due to overheating of the coolant. Let's look at several types of boilers and the common causes of this problem in them.
Boilers with automatic ignition.
Water circulation in the heating circuit is disrupted.
Due to the slow movement of the coolant in the heating system, the water in the heat exchanger overheats and the boiler stops in emergency mode. The speed of fluid movement in the system can be affected by decreased performance or breakdown of the pump, contamination of the filter installed on the “return” of the heating circuit, or improper operation of the three-way valve.
The performance of the circulation pump is reduced due to contamination of the turbine blades or internal cavity.
Photo 1 – circulation pump module of a gas boiler with automatic ignition.
To revise it you need:
- Stop smoothly by moving the water temperature regulator knob to the extreme zero position and wait until the process is completed, turn off the power to the boiler.
- Remove the front part of the housing.
- Determine the installation location of the pump.
- Close the shut-off valve (No. 2, No. 3, No. 4 photo 2) of the supply, return, and cold water supply lines.
- Drain water from the boiler through the drain valve and leave it in the open position.
- Loosen the pump fasteners until air enters the circuit to drain residual fluid from the system.
- Remove the mount, power plug and remove the module (engine with turbine).
- Clean the blades, internal cavity and rubber seal of the mechanism from dirt.
- Assemble the pump.
- Open the cold water supply tap.
- Open the feed tap slightly to check the tightness of the hydraulic part of the boiler.
- Open the flow and return valve.
- Fill the system with water to a pressure of 1 bar.
- Turn on the boiler in circulation mode to remove air.
Photo 2 is an example of heating system pipe routing.
In boilers with electronic control, if the pump breaks down, the corresponding fault code will be displayed on the dashboard, which is deciphered using the boiler passport or electronic catalogs posted on the manufacturer’s website.
Checking and cleaning the filter:
- Smoothly stop the boiler.
- Using the taps (No. 1, No. 2) installed in front of and behind the filter, turn off the water supply.
- Using the filter drain valve, remove water from the isolated area.
- Unscrew the flask and clean the mesh catcher.
- Assemble all filter components.
- Open previously closed valves.
- If system pressure decreases, recharge the circuit.
- Turn the boiler to the venting position.
Checking the three-way valve.
In double-circuit wall-mounted gas boilers, switching from the heating mode to the hot water supply position is carried out using a three-way valve. It consists of a servo drive (motor with gearbox), rod, rubber seals, valve and body with inlets and outlets. A malfunction of this device can lead to a cessation of coolant circulation and, as a result, overheating of the heat exchanger occurs.
To check the condition of the three-way valve, it is necessary to smoothly stop the boiler and de-energize the system. Check the serviceability of the engine, and to do this, connect ohmmeter probes to the power terminals. If it shows 80 - 300 Ohms, then the engine is working, and if there are other readings (0 or 1), then it is faulty.
The three-way valve may not switch due to jamming of the drive gearbox, or due to deformation of the valve itself. If malfunctions of the valve are detected, it is replaced with a serviceable one or undergoes revision.
Boilers with semi-automatic ignition.
Heating equipment equipped with automatic Eurosit 630 or similar is classified as semi-automatic, because the main burners are ignited by the flame of the wick, which burns throughout the entire operation of the boiler.
Reasons and methods for eliminating water boiling in boilers with semi-automatic ignition.
Faulty coolant temperature sensors.
The temperature of the water in the heating circuit is controlled by sensors (thermistors), which are located in the supply and return lines of the boiler. A working sensor changes its resistance when the coolant temperature changes. For example, at 25 0C it will be approximately equal to 10 kOhm, and at 45 0C - 4.913 kOhm. According to the type of design, the sensor can be surface-mounted (reads parameters through the copper wall of the pipe) or submersible (contacts the coolant without an intermediary). If the probes are not inspected in a timely manner, then a non-metallic coating forms on the contact surface, impairing heat transfer and causing their damage.
To study the condition of the thermistor, a tester is connected to the sensor contacts in the ohmmeter position. If it commits:
- the resistance is in the range of 1 - 30 kOhm, which means the sensor is working;
- 1 or 0, the probe must be replaced.
Procedure for replacing the temperature sensor:
- Depending on the type of probe, it is unscrewed or removed from the pipe.
- Before installing a new sensor, for overhead thermistors, thermal paste, for example, MX 4, is applied to the prepared base, from which dirt, oxides, and grease are removed. For immersed probes, the seat is cleaned, and fum tape is wound onto the mounting thread.
If the probe breaks down in automatic boilers, a fault code will be displayed on its dashboard. Also, the coolant may overheat due to a pump malfunction and filter contamination. Methods for identifying and eliminating such problems are described above.
Good afternoon Yesterday we installed 2 additional radiators (white aluminum) into the heating system in a private house, installed them, opened the valves, let the water in, and as the radiator filled with water, they bleed the air through the vent hole as usual. After the work was done, the pressure in the system decreased and, as usual, water was added from the central water supply system (our house is connected to a water supply system that runs next to the house and we add water to the heating system from the central water supply system, everything is connected so that the valve opens - the water has gone). After all this, the boiler began to heat up and boil very quickly (in our house there are 3 circuits in the heating system, through which the first and second floors of the house are heated, each circuit has a pump (3 pieces) and one pump is installed in the return line. So Now, all the pumps are working, the air in all the radiators is bleed, and the boiler continues to heat up very quickly, literally from one thrown firewood, I ask you to help in any way you can, I’ve been suffering for 2 days now, I don’t understand what the reason is.
Unfortunately, knowing almost nothing about the heating system of your home, we cannot help with specific advice. It’s like in medicine: to make a diagnosis, the doctor must receive test results and examine the patient. And we don’t even know the “anatomy”; you didn’t attach a diagram to the question. You need to know not only the general location of the heating devices, but also the structure of the boiler room, the location of the air vents, etc. But, even knowing these parameters, trying to determine the nature of the problem in absentia is largely guessing on tea leaves. There can be many local reasons for the malfunction of the system; we will outline the correct, in our opinion, algorithm for finding and eliminating them:
A manual air vent (Maevsky tap) must be installed on each radiator
Poor circulation can also be caused by general contamination of the system; first of all, the batteries become clogged. The heating device can be removed and blown with compressed air or washed with a powerful stream of water.
The diagram shows that automatic air ventilators on combs (5, 11) and Mayevsky taps (13) are placed on all heating devices without exception. This was done for a reason, but to eliminate situations similar to yours.
The heating system has a rather complex structure and before assembling all the elements into a single network, it must be calculated in detail. In the vast majority of cases, boiling of the heating system is associated with incorrect calculations. There are also often situations when, when choosing a boiler power, a unit is specially purchased with a large performance reserve, which leads to overheating of the coolant.
Boiler is too powerful
Excessive performance of a solid fuel heat generator is the most common reason that causes water to boil in the heating system. To determine the optimal boiler power, there is an average indicator that indicates a sufficient number of kW to heat 10 m² of residential building area. This value is 1 kW per 10 square meters of a house with conventional insulation.
If we take a house of 100 m² as an example, then a 10 kW boiler will handle its heating. Taking into account possible mistakes made during the process of insulating the building, it would be appropriate to place the unit with a small margin of up to 11-12 kW. When purchasing a more efficient heat generator, you should know that during its operation there will inevitably be a need to artificially reduce the power of the device.
Using a boiler at partial capacity is usually practiced in private homes, where the heat generator is selected with excessive performance. It is important to understand that constant operation of the boiler in limited power mode has a very negative effect on the heat transfer rates from the fuel. Its combustion in the furnace does not occur completely and part of the energy is lost due to the low efficiency of combustion of combustible material.
In addition, flue gases in this mode of boiler operation contain a lot of soot and tar. These substances settle on the walls of the combustion chamber and inside the chimney, gradually forming an increasingly thick layer. Over time, the accumulated sediment begins to narrow the lumen of the smoke exit channel, which also causes a drop in the efficiency of the heat generator.
Based on the above, it follows that it is better to use the boiler only at maximum power. It is necessary to prevent boiling of the coolant in the system not by adjusting the intensity of fuel combustion, but by installing an additional buffer tank with water. A special thermal accumulator (TA) is used as such a container. Its volume is determined individually, depending on the parameters of a particular heating system, but usually the capacity of the heat accumulator is in the range from 1000 to 2000 liters.
A properly designed tank is capable of absorbing all the excess heat produced by the boiler. After connecting a heat accumulator to the system, the problem with boiling water will be solved once and for all. No matter how powerful the heat generator is installed, you can always select a buffer tank of appropriate volume for it, which will eliminate any cases of overheating of the coolant.
The heat accumulator is also beneficial because it not only protects the heating from overheating, but also has the ability to store energy. During the active operation of the heat generator, the water in the tank warms up well. And after complete combustion of the fuel in the boiler, the liquid begins to release heat reserves into the system, gradually cooling down over several hours. Thus, the device guarantees the maintenance of a comfortable temperature in the rooms for a very long time after the heat generator has completely stopped.
There are two types of heating systems - with natural and forced circulation of coolant. Heating with natural circulation (NC) works due to the correct installation of all elements, taking into account hydraulic and gravitational forces. Water moves as a result of expansion when heated and decrease in volume during cooling. In addition, the location of each of the elements and the production of the correct slope of the pipes also includes the force of attraction.
Heat systems where water moves as a result of the pressure created by the pump are called forced circulation (PC) systems. The circulation pump is designed to generate a flow of sufficient force to ensure a timely change of hot water in the boiler to cooled water. When the device for some reason reduces the intensity of operation or turns off, the coolant remains in the boiler for too long and begins to boil.
Sometimes improperly designed heating systems experience what is called “cold boiling.” This concept refers to the formation of air bubbles in a liquid in small areas of the hydraulic circuit where significant pressure differences exist. A sharp decrease in pressure in water causes the release of air from it and is called “cavitation”.
Most often, this phenomenon is caused by a malfunction of the circulation pump, since it is the pump that creates areas with different pressures in a homogeneous fluid flow. Cavitation is also one of the reasons for water boiling in the heating system, so it must be eliminated by adjusting the pump. The pressure it creates should not be either too high or too low.
Errors during the installation of the heating system
Compliance with the installation technology of each individual element of the heating circuit is of great importance. If you ignore the recommendations of specialists regarding the installation process of a boiler, pump, expansion tank, or even one single radiator, then there is a possibility of air getting into the water circuit.
In a coolant that contains a certain number of air bubbles, sooner or later air pockets will form. Check the temperature of all radiators, pipes, heated towel rails and other parts of the system that actively give off heat. If some area is cold, then a congestion has formed in it as a result of the accumulation of air in some key places.
From the point of view of system integrity, this state of affairs means a complete shutdown of some part of the network. As a result, the remaining radiators cannot cope with cooling the coolant to the required temperature. With each cycle, the water returns to the boiler more and more heated and after a certain period of time reaches the boiling point.
Regardless of the type of network, whether forced or natural circulation, installing pipes with an incorrectly calculated diameter also sometimes leads to boiling water. It is enough to connect one of the radiators to pipes that are too narrow to slow down the movement of fluid throughout the network. And this, as mentioned earlier, prolongs the period of passage of the coolant through the boiler and causes it to boil.
Another condition, ignoring which is dangerous for the thermal balance of the heating system, is insufficient installation height of the expansion tank. The expansion tank (ER) performs the function of maintaining stable pressure in the pipes. A liquid expands when heated and decreases in volume as it cools. And the expansion tank receives the excess water formed in the overheated system and compensates for the lack in the cooled one.
The tank must contain an amount of liquid equal to at least 5% of the total volume of coolant in the system. And the height above the floor should be at least 2.7 meters if we are talking about a one-story house. For such a construction, as a rule, a tank with a volume of 8 liters is enough, but it is better to place a tank with a larger capacity - from 12 to 15 liters.
How to solve the boiling problem?
In general, after a detailed study of the reasons for overheating of water in the heating system, the answer to the question “What to do?” is found by itself. A detailed study of a specific heating network makes it possible to say exactly which element is the weak link and what can be done with it. If we summarize all the described solutions to this problem, we get the following list:
- Boiler power too high
- Circulation pump malfunction
- Air jams
- “Narrow” places in the circuit that delay the flow of water (pipes, connections, taps, etc.)
- Clogged water filters
It’s worth saying briefly about filters. Often, if the water has a high enough hardness, they quickly become clogged. Typically, such a filter is placed on the return circuit of the cooled coolant outflow. The device should definitely be inspected, since at a certain stage of blockage it begins to block the flow of water, and this leads to the fact that the heating constantly boils.
The most rational and comprehensive solution to the issue of system boiling is to install a heat accumulator. The total amount of water due to this circuit can be increased several times. This is guaranteed to protect the coolant from boiling. A properly selected heat accumulator will increase the total heat capacity of water to such a value that even a very powerful boiler will not be able to boil it.
When choosing a gas boiler, buyers pay attention to the safety system, quality of components, brand and reliability of the manufacturer. But during operation, different situations occur: the boiler boils, stops and blocks operation. How to deal with this problem yourself? Our publication will help you find and eliminate the causes of equipment breakdowns. The main ones are blockages, scale and improper installation.
Why does a gas boiler boil?
During normal operation of the equipment, the coolant in the circuit warms up to the set temperature. After which it is distributed naturally or forcibly through the heating system through the pump. This is how the radiators in the room warm up. The liquid then moves along the return circuit and returns to the boiler.
In case of overheating of the coolant, thermal sensors are activated. As a result, the operation of the device is blocked. What to do if the boiler boils? To restore heating, it is necessary to find the cause of the breakdown. Sometimes the self-diagnosis system displays an error code:
- E01 for " ";
- E02 for ;
- A03 for " ";
- 01 for ;
- F20 for " ";
- 16 for etc.
But if this does not happen, the problem can be identified by external signs.
What causes overheating:
- Clogged filters;
- Air accumulation;
- The heat exchanger is clogged with scale;
- Problems with the circulation pump;
- Failure to comply with regulations for the premises where the equipment is installed.
How to restore boiler operation
If the equipment overheats, do not delay repairs. Occasions happen, so fix the problem as soon as you notice it.
Blockage and airiness of the system
If water stagnates and does not circulate in the circuit, this leads to boiling. You can hear the liquid inside gurgling. Turn off the device and wait until the coolant cools down. Often the filters are valved on both sides so you don't have to drain all the water from the system. Turn on the taps, remove and wash the filters.
If the strainer is very clogged, dip it in a solution of citric acid. Additionally, you can clean the part with a soft brush.
Filters that are worn out and cannot be cleaned should be replaced.
An air lock slows down the movement of the fluid or stops it altogether. How to deal with this:
- Open the Mayevsky taps - they are on every radiator. Place containers under them first;
- You will hear air hissing out of the circuit. Then water can flow. Do not close the taps immediately. Wait until the liquid is drained and all the air is released;
- Repeat the procedure until the air lock is completely eliminated.
Scale deposits
Magnesium and potassium salts are deposited on boiler parts when heated above 55 degrees. Most of the scale deposits in the heat exchanger because the liquid circulates and heats up in it. As a result, the passages in the tubes narrow, the pressure decreases, and water boils in the assembly. This leads to overheating and damage to the heat exchanger.
To clean the unit, remove it. The most effective way is to connect a pump to the unit and pump it with the reagent. After this, the radiator is washed with running water, dried and installed in place.
At home, the radiator is placed in a metal container with warm water. A solution of citric acid is poured into the coil. The container is placed on the stove, where it warms up for half an hour.
To prevent scale formation, install magnetic filters. Their cassettes only need to be changed once a month, but they soften the water well.
Problems with the pump
When turning on the boiler after a long period of inactivity, you need to check the pump. Its parts could stick and the holes could become clogged. Clean and replace faulty parts.
Installation problems
When installing the boiler in a room with high humidity, the risk of corrosion increases. This leads to a violation of the tightness of the system, leakage of coolant and gas. Therefore, before choosing a place for equipment, read the requirements for it.
Be careful with gas equipment. Once a year, carry out breakdown prevention and technical inspection.
Last winter I had a misfortune. The heating boiler leaked. The time has probably come for him. For ten years it worked flawlessly, and then from the blower, at first little by little, and then more and more, it began to pull out raw slag. Everything would be fine, change the boiler, and that’s all. But it's winter outside. The frost is in the thirties, so I had to add water to the system every day. And so he lived until spring. At the beginning of March I purchased a new boiler. I spent a long time choosing from different options and finally settled on the Krasnoyarsk boiler “Dymok”, with a power of 18 kW. I won’t go into details about replacing the boiler, that’s not what I’m talking about.
After starting up the new boiler, I encountered the following problem: the cauldron is boiling. I started researching this issue in more detail. An old boiler of approximately the same power did not boil. And this is the conclusion I came to.
Why is the cauldron boiling??
First reason The problem is that there is an air lock somewhere in the system. I went through the entire heating system, determined where the hot water reaches, and then warm water goes further. Air was released through the plugs. It's gotten better, but the boiler is still boiling.
The second reason The thing that I noticed is that the boiler heats the water very quickly, and I have a large heating system. There are approximately 20-25 buckets of water in the entire system. I don't have a circulation pump. It’s just hard for the boiler to quickly disperse such an amount of water.
The expansion tank is connected to the system at the highest point, above the boiler. The hose connecting the heating system to the expansion tank was quite short and connected the heating supply pipe and the tank almost in a straight line. And as a result, it turned out that it is easier for the boiler to push boiling water into the expansion tank than into the heating system.
To solve this problem, I extended the hose so that it now hangs below the level of the supply pipe, and even forms a loop. Now the hot water needs to go down, go through the loop and only then get into the expansion tank. It’s easier to go up into the heating system.
Of course, I did not completely eliminate the boiling problem. Still, a circulation pump is needed. But now the boiling occurs in very short intervals. As soon as it starts to boil, you can immediately hear the characteristic sound of water moving in the pipes. A new portion of water boils and starts moving again
This is how I solved the problem when the cauldron is boiling.
