The main purpose of a gas boiler is to heat the room. In other words, the boiler works for heating. But such one-sided functionality is available only to boilers with one heating circuit. Double-circuit boilers are becoming more popular and in demand today. Their main difference from the previous type is the ability to work for hot water supply (DHW), thanks to the presence of a second heating circuit.

 

According manuals online double-circuit boilers have gained great popularity due to their ability to provide greater comfort in domestic use. However, it is easy to assume that a double-circuit boiler is a somewhat more complex device, compared to its single-circuit counterparts. Consequently, such boilers require more thorough maintenance, and boiler repairs , in the event of breakdowns, will be more complex and thorough.

 

How does a double-circuit boiler work?

 

The main difference between a double-circuit boiler and a single-circuit boiler is the presence of a secondary heat exchanger, which is capable of heating water in the DHW mode. Thus, the boiler does not operate to heat the room, but as a flow-through water heater. The main advantage of this mode is that there is no need to install a separate boiler for heating water.

 

Both types of boilers, both single-circuit and dual-circuit, work the same way to heat a room. First, the boiler pump is turned on, which drives the coolant, most often water, through the heating radiators. The sensor measures the temperature of the coolant, if it is lower than that set on the control panel, the burner is turned on and the heat exchanger is heated. The coolant receives heat from it and heats itself.

 

Upon reaching the set temperature, the burner switches off, but the pump continues to operate for some time. After about a minute, the pump also stops. As soon as the coolant cools down, the process starts again.

 

The main difference between a dual-circuit boiler and a single-circuit boiler is the presence of a secondary heat exchanger. When hot water is turned on at the tap, a valve is triggered in the boiler, which directs the water to the secondary heat exchanger. It gradually heats the water, when the tap is closed, the valve is triggered again and the water is directed to the primary heat exchanger.

 

In the case of the primary heat exchanger, the pump runs for a while after the heating has stopped to give the heat exchanger time to cool down, otherwise the water may boil. The secondary heat exchanger does not heat the water above 80°C, so boiling is impossible.

 

Why doesn't the boiler heat water?

 

Under normal operating conditions, a double-circuit boiler operates for heating and hot water supply. However, there are a number of malfunctions that can disrupt the normal operation of the device; it can continue to operate for heating the room, but will not heat the water.

 

Three-way valve clogged with scale

 

A three-way valve in a gas boiler design is designed to redirect the water flow from the primary heat exchanger to the secondary one. This is necessary so that heating occurs not for heating, but for supplying hot water. Water for these purposes is heated in the secondary heat exchanger.

 

The valve itself does not participate in heating the water, but scale can appear on it and make it difficult to switch. During the heating process, the scale layer can build up, and subsequently some parts peel off and get into various elements of the gas boiler in the water flow, for example, into the three-way valve.

 

The accumulation of scale in the valve complicates its operation and subsequent switching to the flow-through water heater mode. As a result, the gas boiler gradually stops working on hot water supply, and only cold water will flow from the tap.

 

The solution to the problem is to clean the valve from accumulated scale; in the most advanced cases, a complete replacement of the part may be required. As a preventive measure, it is necessary to think about installing an additional filter that will reduce the amount of impurities in the water.

 

The flow sensor is faulty

 

The design of a gas boiler includes several sensors that are responsible for the correct operation of the device. We have only superficially examined the operating principle of a double-circuit boiler, but even so it is clear that the boiler switches to the flow-through water heater mode when hot water is opened in the tap. This mode is possible thanks to the flow sensor.

 

The sensor itself is presented in the form of a fan, which rotates under the influence of water pressure. Therefore, if the fan rotates, it means the tap is open and it is necessary to switch to the DHW mode. After the flow sensor starts rotating, the three-way valve is triggered and the water begins to heat up.

 

From this it is clear that if the flow sensor is faulty, the three-way valve will not switch to the DHW mode, the water will not heat up. As a rule, the sensor stops functioning normally due to a serious blockage. There are two options for cleaning the fan. The first is to shut off the common water riser, open the hot water and drain it as much as possible, then close the tap and simply turn on the water.

 

The air that passed through the pipes during the process should clean the fan. If this method is useless, it is necessary to partially disassemble the housing, remove the sensor and clean it manually.

 

The flame sensor is faulty

 

Another sensor in the design of a dual-circuit boiler that can affect the heating of water in the DHW mode is the flame sensor. This sensor is designed to control the presence and strength of the flame in the burner so that the water is not too hot or, conversely, is hot enough, depending on the settings made on the control panel.

 

The flame sensor is a thin wire that is located above the burner. In order for the sensor to continue to function properly, it must be located at a certain distance from the flame. However, in practice, there are cases when, under the influence of high temperatures, the sensor is deformed and changes its original location.

 

As a result of deformation, the sensor stops performing its functions, the flame becomes either weak or completely absent. Due to this, the water either heats up weakly or does not heat up at all. There are also rarer cases when, as a result of deformation of the flame sensor, the water, on the contrary, heats up too much.

 

To restore the boiler functionality, it is necessary to return the flame sensor to its original state.

 

Low water pressure

 

For normal operation of the gas boiler in both modes, a sufficient level of water pressure in the system is required. Otherwise, the water will not heat up for either heating or hot water supply.

 

Low water pressure in the water supply system may be a temporary phenomenon, for example, caused by preventive maintenance work by public utilities. However, if such work is not carried out, it is necessary to visually inspect the valves and pipe joints. The valves must be open enough for normal water flow, and there should be no leaks at the pipe joints.

 

If a leak is detected, it must be localized and eliminated as soon as possible. If no leaks are detected, but the water pressure remains low, it is necessary to fill the expansion tank with water, this will help eliminate the incorrect operation of the boiler, but only for a while.

 

Scale in the heat exchanger

 

A gas boiler, both double-circuit and single-circuit, belongs to the category of climate control equipment. Devices of this type are capable of providing our home with warmth and comfort, but they also require regular preventive cleaning. If this need is ignored, the operation of the gas boiler will soon be disrupted.

 

One of the main requirements for prevention is cleaning the boiler and its elements from scale. Often, the formed scale gets into the heat exchanger and accumulates in it, as a result of which normal water heating is disrupted. A clear sign that the heat exchanger needs to be cleaned from scale is when the water from the tap is cold, gradually warming up weakly, but very quickly becomes cold again. The burner starts working, but soon goes out.

 

It is better to clean the heat exchanger in a comprehensive manner. Comprehensive cleaning involves manual mechanical cleaning, after which it is replaced by chemical cleaning, which involves washing with chemicals.

 

To carry out mechanical cleaning of the heat exchanger, it must be dismantled, which implies partial disassembly of the boiler and some of its associated elements, so it is better to invite a specialist for such work.

 

Methods of cleaning a gas boiler

 

To avoid having to solve problems with water heating, the gas boiler should be regularly subjected to preventive cleaning. It is necessary to clean the boiler from accumulated scale, primarily the heat exchanger, as well as from soot and carbon, which also accumulates during the operation of the device.

 

Preventive cleaning of the heat exchanger from scale is carried out mechanically or chemically. In the case when cleaning from scale occurs not as a result of a malfunction, but for preventive purposes, complex cleaning can be omitted, and one option can be chosen that is most suitable for you.

 

The burner, nozzles, gas pipes, chimney, tubes, etc. are cleaned from soot. To clean from soot, you will need several brushes - soft and hard, a brush, a couple of rags or rags, keys for disassembling the body.

 

Cleaning of boiler elements from scale is carried out approximately once a year, but the frequency may vary depending on the degree of water hardness, the use of filters for cleaning and softening water. It is possible to clean the boiler from soot and carbon less often, depending on the intensity of use, cleaning is recommended to be carried out once every two to three years.