What to do if a gas boiler breaks down and hot water does not turn on? Diagnostic and repair instruction

Vasily Borutsky
Checked by a specialist: Vasily Borutsky
Author: Sergey Shapoval
Last update: December 2019

The installation of a double-circuit gas boiler can effectively solve the issue of hot water supply. But what if the hot water in the gas boiler does not turn on? Agree that you should not immediately panic and call the rescue service or service center.

We will get acquainted with the principle of operation of the double-circuit boiler, tell about the reasons that can lead to the interruption of the supply of hot water and ways to eliminate the problems that arose.

Understanding the essence of the equipment, you can not only independently identify the causes of a malfunction, but also eliminate most of the malfunctions, as well as restore the supply of hot water in full.

The principle of operation of a dual-circuit gas boiler

To understand why a gas boiler began to heat water poorly or there is no hot water supply at all, you need to understand how it works dual circuit unit. Almost any gas equipment of this type is equipped with several units.

In the main site provides ignition of the gas mixture and its combustion. An additional water unit provides a level of hot water supply and monitors the pressure in the line. For the removal of combustion products outside the housing unit is responsible flue.

When the equipment is started, the pump is activated, which pumps water into the system. The liquid begins to circulate through the tubes of the heat exchanger, where it is evenly heated due to the action of the burner.

Double-circuit boiler operation scheme
The boiler has two circuits, one of which is responsible for heating, and the second for the operation of hot water. Simultaneous operation of two circuits is not possible.

The heating process is controlled sensors or a simple mechanical system or gas boiler automation, depending on the model and complexity of the device.When the set temperature is reached, the gas supply stops. When the temperature drops to a critical value, the burner starts up and the cycle repeats.

Distinctive operation schemes of double-circuit boilers

If there are problems with hot water supply, it is necessary to understand the scheme of the gas unit in the DHW mode to find out the reasons. There are two options with a bithermic and secondary heat exchanger.

Bithermic heat exchanger boiler

The principle of operation of the unit with a bithermic heat exchanger is associated with the configuration - in fact, this is one tube of complex shape located inside another. The coolant moves along the outer section of the tube, and the domestic hot water moves along the inside.

When operating in heating mode, the burner heats the coolant to a predetermined temperature and turns off. When the hot water tap is opened, fluid movement begins along the internal circuit of the heat exchanger, and at the same time, the external circuit blocking valve is shut off.

Bithermic heat exchanger
In double-circuit boilers with a bithermic heat exchanger in one heat exchanger, there are simultaneously internal and external circuits responsible for the operation of heating and hot water

The burner operates continuously at maximum power, providing heating of running water. After closing the tap, the coolant supply valve opens, and the boiler starts to work as usual.

Secondary heat exchanger boiler

In another type of boilers with a secondary heat exchanger, the principle of operation is slightly different. Not only the second circuit is responsible for heating the water, but a separate plate heat exchanger equipped with a three-way valve.

Secondary heat exchanger
A secondary heat exchanger is preferable to a bithermic one - it is easier to remove for washing and cleaning.

When the hot water tap is opened, the heat carrier is redirected from one heat exchanger to another, where heat is transferred to the flowing water. At the same time, the pump continues to work, providing a coolant pumping along a small circuit.

Natural and forced circulation system

The reasons why gas boilers stop heating water may also depend on the way the coolant circulates. But this is more connected not just with water heating, but with the operation of the device itself. The reason for the poor operation of the boiler, included in the circuit with natural circulation, is either non-compliance with slopes or the presence of air jams.

In heating circuits with forced circulation such a problem is absent, since the coolant moves through the system under the influence of a circulation pump. Further, we will not dwell on the operation of the gas boiler itself, but we will consider exclusively the problems of hot water supply, assuming that the boiler functions normally in heating mode.

What to do if the boiler does not heat water?

When combining the functions of heating and hot water supply in a boiler, situations often arise when the heating system is working and there is no hot water. DHW problems can also manifest themselves in another form - the volume of heated water may be insufficient or the temperature is lower than required.

In some cases, a situation may occur when hot or cold water flows from the tap. There is also a reasonable explanation for this, and the reason for such a phenomenon is also easily eliminated.

Secondary heat exchanger clogging

Overgrowth of the heat exchanger by salt deposition is the most common cause of a decrease in the efficiency of hot water supply. As a result of the formation of scale, not only the volume of the heat exchanger decreases, but also a significant decrease in water temperature occurs.

Scale in the heat exchanger
Scale reduces the volume of fluid permeability along the circuit, and, deposited on the walls of the heat exchanger, reduces its thermal conductivity

This is due to the fact that water is not in contact with the metal of the heat exchanger, but with scale, the thermal conductivity of which is significantly lower. The scale is very unstable, it can crack and exfoliate.Even a small piece or plate of scale can simply block the fluid flow.

There are two ways to clean the heat exchanger - mechanical and chemical. The first one is very troublesome and its effectiveness is much lower. In addition, in some models, independent dismantling of the heat exchanger can be not only difficult, but also almost impossible.

Chemical cleaning of a bithermic heat exchanger

Flushing is carried out without dismantling the heat exchanger; a booster of 20-30 liters is required to complete the procedure. Before starting work, drain coolant from the heating system using a Maevsky crane.

Fill the booster tank with flushing solution, and lower the hoses into the tank, the free ends of which are connected to the pipes of the heat exchanger. The movement of fluid is possible only under the influence of a circulation pump, it must be connected to one of the hoses.

Flushing the bithermic heat exchanger
The ends of the hoses must be put on the nozzles of the heat exchanger, and the free ends should be placed in the booster with flushing fluid by connecting a circulation pump. Work can be done without removing the heat exchanger

It is ideal to connect a reversible pump with the ability to change the direction of fluid flow. It remains to start the boiler for heating with a given temperature of 50-60 degrees and leave it for 15 minutes, periodically changing the direction of circulation.

Chemical cleaning of the secondary heat exchanger

Flushing the secondary heat exchanger of the double-circuit gas boiler can be performed similarly to flushing the bithermic heat exchanger. However, it must be taken into account that the secondary heat exchanger is easily removed, therefore, it is possible to improve the quality of cleaning by disassembling it.

To gain access to the heat exchanger, it is necessary to dismantle the front panel of the unit and move the control unit to the side. The heat exchanger is fixed with two bolts in the lower part, turning them out, you can easily remove it.

Most efficiently extracted from a regular place flushing heat exchanger place in a container with a salt-dissolving solution and boil. Instead of a suitable household product, you can use a 20% solution of citric acid.

Boiling the heat exchanger
Good results can be achieved by boiling the secondary heat exchanger in the washing solution.

When cleaning any heat exchanger, rinsing with clean water is carried out at the final stage. This measure is necessary to remove traces of a chemically aggressive substance and stop its effect on the walls of the heat exchanger.

There is another way to clean the heat exchanger - hydrodynamic. Its implementation requires special equipment and pressure control at each stage of cleaning. Therefore, without special knowledge and skills, its independent implementation can be dangerous.

Regular cleaning of the heat exchanger will eliminate the need to use very aggressive compounds and will make it possible to extend its service life. Recommended annual cleaning of the heat exchanger at the end of the heating season.

Flow sensor problems

A possible reason that the gas boiler may stop heating water is a problem with the flow sensor. The device is a small fan that rotates under the influence of a stream of water. As a result of rotation, a signal is supplied to the control board for heating the water. Due to clogging, the fan may stop rotating.

You can eliminate clogging without resorting to dismantling the device. For cleaning, just open and close the water tap several times. If such actions do not give the desired result, then you will have to remove the sensor and carry out its cleaning.

To do this, you must:

  • Disconnect the gas boiler from the mains;
  • Turn off the water tap;
  • Drain the water from the unit.

Typically, the duct sensor is attached with a bracket, removing which, you can easily remove the device.The assembly is removed completely in order to remove the inside, it is necessary to turn the parts in the groove. During disassembly, clean the filter screen and remove the turbine.

Often, turbine blades are coated with a layer of rust that needs to be cleaned well. If you remove the three clamps, then you can take out the turbine itself to clean the inner plane of its landing. Now it remains to assemble in the reverse order.

Cleaning the duct sensor
When disassembling the flow sensor, clean the filter and turbine blades.

If cleaning the duct sensor does not bring the desired result, and there is no hot water, then the entire assembly will have to be replaced.

DHW sensor malfunction

The problem manifests itself in the fact that the boiler starts, but after a few minutes it goes out, giving an error code. This indicates a malfunction of the sensor that determines the temperature of the water supply to the DHW circuit. To find out if the sensor is working, it is necessary to measure the resistance with a multimeter.

Having looked at the instructions, you need to verify the result with the actual temperature of the sensor. If the sensor at room temperature shows a result corresponding to a water temperature of 60 degrees, then it is obvious that the sensor is defective and needs to be replaced.

Given that the sensor is in direct contact with water, to replace it, you will need to not only turn off the water supply tap, but also completely reset the pressure.

Three-way valve problems

If when turning on the hot water supply, it is noticeable that the gas boiler slightly warms the water or the water flows completely cold, then this indicates the circulation of the coolant only along the heating circuit. The reason is clogging or failure. three way valve.

As a rule, a three-way valve fails due to excessive pollution. In addition, as a result of operation, rod wear may occur, failure of the electric motor due to loss of tightness. To remove the three-way valve, you must disconnect the boiler from the network and drain the water from the system.

Three-way valve
With your own hands, you can clean the three-way valve, in case of more serious breakdowns, it is better to contact a specialist or make a complete replacement yourself

The problematic node must be disconnected from all tubular connections, as well as disconnected all electrical wires. Then the three-way valve can be removed for inspection and cleaning. Be prepared for the fact that when you turn off the tubes, some water may spill out.

Most often, inside the three-way valve, residues of scale are found that interfere with the normal passage of water. After removing them, the device performs its functions again. If the motor that moves the inner ball fails, it is better not to resort to repair, but to completely replace the entire assembly.

Conclusions and useful video on the topic

The following video will introduce the progress of cleaning the duct sensor:

A double-circuit gas boiler is a rather complicated device, the repair of which is not always possible with your own hands. But if there are problems with the water supply, then it is possible, based on the material presented, to independently determine the cause of the breakdown.

Knowing about which components and parts affect the operation of the hot water supply and taking timely preventive measures, it is possible to ensure long and uninterrupted operation of the equipment.

Want to talk about how you restored the effect of the hot water preparation circuit with your own hands? Do you have useful information on the topic of the article? Write comments, please, in the form below the block, ask questions, post photos on the topic of the article.

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