When problems arise with preparing hot water in a double-circuit boiler, you must first determine how the boiler operates in DHW mode. There are two options: bithermic heat exchanger and secondary heat exchanger.
In the first case, the heating circuit and the hot water circuit are combined in one heat exchanger - the primary one. When it is necessary to prepare water, the heating circulation pump stops working and all the boiler power is transferred to the flowing tap water.
In another case, the boiler is equipped with an additional (second) plate heat exchanger and a switch (three-way valve). When it becomes necessary to prepare water, the coolant from the heating circuit is directed to a second heat exchanger, through which the heat is transferred to the flowing tap water. At the same time, the pump continues to work - pumping the coolant in a small circle.
Therefore, hot water problems must be diagnosed differently for different circuits.
Most frequently encountered problems:
Baxi boiler does not heat hot water well
Baxi boiler does not heat water (hot water does not turn on)
If the boiler does not turn on when necessary
You open the mixer tap, but the boiler does not react and does not try to ignite the burner, and no errors occur. Regardless of the operation scheme of the boiler’s DHW circuit, a sensor is installed on the outlet pipeline, which detects that water collection has begun. It is also called a DHW flow sensor. Sensors come in different types: some simply detect the presence of water movement in the pipeline, others can quantitatively measure flow. The latter are used to provide greater comfort due to precise control of the burner power depending on the flow rate.
In both cases, when water flow begins, a signal must be sent from this sensor to the control board. If for some reason this does not happen, the boiler will be inactive.
The sensor type is most easily determined by the number of contacts. Two means it is a closing microswitch. Three – sensor with flow meter.
Sensor diagnostics
If the flow sensor is a microswitch, then for diagnostics it is enough to check the contact closure with a tester. To do this, disconnect the contacts from the sensor, connect the tester in “dialing” mode, and turn on the water tap. If a short circuit does not occur, it means that the sensor is faulty and requires inspection and, if necessary, replacement. It happens that accumulated dirt interferes with the circuit and it is enough to clean it. Poor quality of tap water and lack of pre-filters are the most common problem. Reed sensors contain a magnet, so they attract microparticles of rust and quickly fail.
Sensors with a flow meter record the amount of water flow, which can usually be displayed on the boiler display. For BAXI boilers you need:
hold the “i” button to access the information menu for 5 seconds
Use the DHW temperature adjustment buttons to scroll to parameter A08 (actual flow rate of water passing through the sensor, liters per minute * 10)
Now all that remains is to compare the actual water flow from the tap with the flow according to the sensor. If the actual flow rate does not correspond to the sensor value, then most likely it needs to be replaced.
Since the mechanical part of the flow sensor is a turbine, if it gets dirty, it can jam and the signal from the sensor disappears. There is no signal from the flow sensor - the boiler stops heating water.
Three-way valve
A three-way valve is installed in boilers with two heat exchangers. When a signal is received from the flow sensor, the electronics gives a signal to the valve and the heated water from the first heat exchanger is sent to the second heat exchanger, where the heat is transferred to the passing tap water. If, for example, no actual switching occurs (the valve is faulty), then the coolant will continue to circulate in the heating circuit and no heat transfer to the hot water circuit will occur.
If, for example, a valve only partially closes the heating circuit due to a malfunction, then there will be problems with insufficient heating of hot water, since part of the heat will go to the heating system.
Work principles
Gas boilers, as a rule, have two circuits - heating and water heating. Double-circuit devices are a combination of several blocks responsible for a certain functionality of the system. Thus, the gas block is responsible for igniting and burning the burner, which allows the heat-conducting liquid to heat up, the water unit supplies water and ensures the necessary pressure in the line, the smoke exhaust unit releases combustion products into the environment, the control unit controls the operation of all boiler systems.
When the unit is started, water is pumped into the system using a pump, passing through the heat exchanger pipes. As soon as the liquid has entered the water unit, the gas supply valve opens and the burner is ignited. The process of heating the heat exchanger body occurs evenly and is controlled by temperature sensors.
Important! The heating cycle is regulated by sensors. When the water temperature drops to a certain temperature, it is the sensors that transmit an impulse to the control module to resume heating
When hot water enters the mixer, a flow sensor is connected. A signal is sent from it to the board, after which the three-way valve is activated and switches to heating the water supply.
Modulation errors on the burner
To heat running water, in most cases a boiler power close to maximum is required. In modern boilers, the burner power is regulated over a wide range. The adjustment occurs by changing the amount of gas supplied by the gas valve. The amount of adjustment is determined by the control board depending on the operating logic and settings. The process can be observed visually by the height of the flames on the burner.
If the boiler settings are set to 100% boiler power in DHW mode, but visually the flames on the burner are weak, or obvious interruptions are visible, then you should check:
setting the gas valve (static and dynamic gas pressure)
Such checks should only be performed by a qualified person.
Gas pressure at the entrance to the house has decreased
A gas boiler may not reach temperature due to low gas pressure. Typically, a sensor is installed at the entrance to the boiler to measure pressure. First of all, its indicators are checked to make sure of this malfunction.
Also read with this article: What to do if the pressure in the gas boiler increases
Modern heating equipment is often equipped with a pressure reducer. Adjusting the values on it helps solve the problem described. For private houses with one or two floors, the optimal value is from 1.5 to 2 atmospheres. In houses with more than two floors, the gas pressure should be in the range from 2 to 4 atmospheres.
ATTENTION. Any boiler adjustment requires a careful approach with preliminary study of the instructions. Gas is a dangerous flammable component that can lead to explosions and fires if consumed incorrectly. If you doubt your own abilities, contact a company that services gas installations.
Temperature sensor malfunction
The boiler determines the actual hot water temperature based on the readings of the temperature sensor. Therefore, if for some reason it receives incorrect readings, the boiler may not operate correctly in the hot water preparation mode. The temperature sensor is a thermistor with resistance depending on temperature. Testing such a sensor consists of measuring its resistance at a known temperature. Baxi boilers are equipped with NTC sensors with an inverse dependence of resistance on temperature. At room temperature, the sensor resistance should be approximately 10 kOhm, at a temperature of 45 degrees 4.3 kOhm.
Gas filter clogged
It is installed at the inlet of the boiler to further filter the incoming gas. Protects heating equipment from substances that cause malfunctions. A clogged gas filter delays the flow of gas, which reduces the combustion force, and accordingly the temperature in the house will drop.
The degree of contamination is assessed visually when the filter is unscrewed from the boiler. It is necessary to perform such a manipulation when the equipment is completely turned off.
Attention: A dirty filter must be replaced with a new one.
Heat exchanger clogged (reduced throughput)
Often the fouling of the internal walls of the heat exchanger with scale or mud deposits is the cause of problems with hot water. If tap water does not undergo pre-filtration (rough cleaning) and the temperature of the hot water is too high, the walls of the heat exchanger become overgrown with scale and dirt over time, reducing their thermal conductivity and flow area. Each time the user increases the DHW temperature on the boiler more and more in order to obtain the desired result on the mixer. As the temperature rises, scale forms even faster and, as a result, the temperature of the boiler's hot water supply is at its maximum, and the water does not heat up enough. This process has a particularly negative effect on a boiler with a bithermic heat exchanger. Plate heat exchangers are easy to clean.
Control board errors
The control board should be considered as the cause of hot water problems when all other checks have failed. The cause may be a malfunction in the flame modulation circuit. The boiler control unit constantly adjusts the burner power depending on the conditions, and if there is a fault on the board, the boiler can spontaneously reboot or turn off when it reaches maximum power, which in most cases is required precisely in the hot water preparation mode.
It is also possible that boards may be configured incorrectly as errors. But this only applies to those cases where problems appeared after its replacement. BAXI boards are universal and require customization for a specific boiler.
About the disadvantages of reducing boiler power settings
The service instructions for the Protherm Gepard 23 MTV boiler indicate its efficiency in heating mode: 93.2% at maximum thermal power (23.3 kW.) and 79.4% when operating at minimum power (8.5 kW.) Imagine how The efficiency will further decrease if this boiler has to operate with a minimum power of 4 kW. Please note that during the year, a double-circuit boiler operates most of the time in heating and hot water mode with minimal power. At least 1/4 of the spent gas will literally fly uselessly down the pipe. But clocking, as mentioned above, also reduces the efficiency of the boiler, leads to excessive consumption of water and gas, and makes using water uncomfortable.
“The manufacturer set the minimum and maximum boiler power for a reason. According to you, if it were all that simple, then the manufacturer, with the help of its service representatives, would reconfigure the boilers the way you talk about it. But in these cases the manufacturer insists on fighting the pressure and not the boiler. As I understand it, this is due to the fact that changing the minimum/maximum range on the burner is dangerous, especially for the boiler. If you reduce the pressure of the gas supplied to the burner, will the flame go down, in which case will the burner be damaged over time?
And this is my answer to Sergei: “My boiler has been running for five years now. Every year in the summer I clean and inspect the burner. I don't see any signs of damage or overheating. I do the same for others. There is no protection against low gas pressure on boilers. This means that the manufacturer believes that it is not dangerous. Low pressure is dangerous for boilers with burners in which gas is pre-mixed with air and the finished mixture leaves the burner. Then yes, at low pressure, the flame can even jump inside the burner and really damage the burner. Most household boilers have a different burner. There is a danger of the flame going out or blowing out, but boilers have protection that will turn off the boiler and give an error. The choice is up to the owner - either live with the clock, or change the settings, or buy a boiler or another boiler. Manufacturers, sellers and specialists actually deceive buyers, with rare exceptions they do not inform them about the clocking of a double-circuit boiler at low water flow rates. Buyers think that there will be normal hot water at the minimum flow rate specified in the instructions, but then it turns out that this is not the case. Resetting greatly reduces the efficiency of the boiler. This information is not included in the instructions and descriptions for users. If all this was explained to customers, they would buy other boilers.”
Design features of the gas boiler Baxi (baxi), Navien, Ariston
In any case, it will be useful to become familiar with the equipment of this class and the features of modern models. This knowledge will help you choose the right equipment and avoid making mistakes during operation.
In household boilers Baxi (baxi), Navien and Ariston, gas, diesel and solid fuel are burned to heat water, and electric heating elements are used. To more fully utilize the potential of energy resources, heat exchangers are being improved. They make long ducts of complex shapes to ensure that the liquid remains in the working area for a long time.
The current trend is compactness. Manufacturers offer gas boilers with square bodies of relatively small thickness. Some models, due to their aesthetic characteristics, deserve to be placed in a prominent place.
The next feature is the introduction of automated control systems. They control the combustion process, change operating modes taking into account the readings of temperature sensors on the street and in individual rooms. If the equipment overheats, it turns off without user intervention.
It is necessary to carefully consider situations when the Baxi gas boiler does not heat the water. This happens, for example, when the supply of energy resources is cut off. It is not difficult to carry out an appropriate check even without special professional training.
Circulation pumps, valves, and other typical components and assemblies rarely fail. Their designs are designed for many years of operation without mandatory maintenance. Electronic circuits have no moving parts at all. Their breakdowns occur due to defects. Subject to the rules established by the manufacturer, the service life of modern gas heating boilers is more than 10 years.
Problems with the heating circuit
A clogged filter on the return line in the heating circuit leads to problems in the hot water supply.
Often, the reasons for a malfunction in the functionality of the main line are malfunctions in the wiring:
- return filter clogged;
- incorrect installation of the heating circuit;
- insufficient pump power.
It is recommended to eliminate all of the above problems during preparation for the heating season, otherwise you will have to stop the operation of the unit and completely drain the coolant.
To eliminate clogging, the filter is cleaned, the circuit is washed, and the coolant is completely replaced with a new one.
A lack of power occurs due to the presence of branches located remotely from the pump or due to insufficient performance of the device. As a result, the equipment overheats, energy consumption increases, the batteries do not heat up to the required temperatures or remain cold. In this case, there is only one way out - replacing the pump with a more powerful analogue.
If there are errors during the installation process - an incorrectly selected line slope - it is recommended to redo the wiring, entrusting this matter to professionals.
Troubleshooting: why does a gas boiler not heat hot water well?
If a gas boiler does not heat hot water well due to a clogged or ruptured tube in the heat exchanger, repairs are necessary. It is performed by replacing a failed unit. In this case, threaded connections are not used, so disassembling and subsequent installation yourself will be difficult. To create a high-quality connection by soldering, it is better to invite an experienced craftsman. A qualified specialist will ensure the required level of quality and provide written guarantees.
Finding out about the problem in advance is not easy. The scale layer grows slowly, so it will not be possible to register a clear decrease in power. Extraneous noise can be caused by the passage of sand and other mechanical impurities through the pipes. Technological openings are too small for visual inspection. To complete this, dismantling is required.
The information provided explains why emergencies of this type occur unexpectedly. To prevent them from developing into a more complex problem, you can equip your boiler equipment with a modern remote monitoring system. Some manufacturers offer ready-made solutions in the form of an additional electronic unit and specialized software.
The corresponding application is downloaded to the smartphone. The advantage is the ability to remotely change settings and check temperature sensor readings. If the Navien gas boiler does not heat hot water due to scale, replacing the heat exchanger is not enough. These same contaminants reduce the internal diameter of pipes and narrow the ducts in radiators. A complete cleaning of the system is necessary.
This procedure is performed according to the following method:
- Pour the water into the drain.
- Rinse all circuits sequentially or simultaneously with a special solution.
- It is also used to clean the heat exchanger if it is only clogged and can be used further.
- After assembly, the functionality of the system is checked under pressure.
- Eliminate identified defects (cracks, loose connections).
To remove calcium solutions, magnetic water converters mws or aggressive chemical compounds are used. The duration of the standard procedure for one household object is several hours. Appropriate corrections are made taking into account the actual state of the system. Strong acids can damage metal parts and solder joints of an Ariston double-circuit boiler. For this reason, experienced teams take repair tools to complete orders.
It is possible to carry out such procedures independently. But for many ordinary users it is not advisable for several reasons:
- You have to purchase expensive equipment for pumping liquids that will be used.
- Independent selection of the optimal composition of the solution will cause difficulties.
- During this procedure, there are no mechanisms for operational control of processes within the pipeline system. This increases the likelihood of breakdowns.
- When performing transactions in person, you will not receive official guarantees from a third party. Any problems that arise in the future will have to be resolved at your own expense.
Additionally, it should be noted that careless handling of aggressive chemical compounds can cause harm to health.
Preventive actions
Specialists from companies offering flushing recommend doing this every heating season. It is combined with a general inspection of the equipment. The frequency is adjusted taking into account the level of rigidity, the intensity of operation of Baxi gas double-circuit boilers, and other significant factors.
Tips like this are really helpful. Regular cleaning will prevent more complex procedures. Simultaneous testing will help identify problems at an early stage. However, it is necessary to emphasize the main disadvantage of this technology - it itself can damage the equipment. It is especially unpleasant if defects appear during the heating season. It will be quite difficult to prove the guilt of the workers who did the cleaning.
Prevention and cleaning methods
The heating circuit in the boiler is clogged with scale and needs to be cleaned
. Many gas boilers do not heat water because preventive measures have not been taken beforehand. Heating equipment requires timely maintenance:
- cleaning;
- replacement of components and worn parts, gaskets, seals;
- gas adjustment;
- pressure control.
It is also important to ensure that the coolant level in the expansion tank is correct.
If the Baxi boiler does not heat water due to contamination of the OS elements, it is necessary to clean it. There are several ways:
- Mechanical. It is produced with scale thickness from 1 mm to 3 mm using equipment made of a flexible shaft, with a drive and cutters.
- Hydrodynamic. Occurs by flushing pipes with high pressure water.
- Chemical. For the event, specialized equipment and a composition of aggressive effects on the surface are used.
- Electric discharge. The method allows you to remove high-strength contaminants. A working cable with a certain power/frequency of electric discharge is transported along a water-filled line.
The cleaning method is selected taking into account the type of boiler, the nature of the contamination and the thickness of the scale.
