How Do Combi Boilers Work ?

Combi boilers have become one of the most important components of modern home heating systems. These devices, which meet both heating and hot water needs, provide a comfortable and efficient living space in homes. 


A combi boiler is a compact device that provides both a central heating system (radiators) and instant hot water. It is usually installed in the kitchen, bathroom, or another suitable area of the house. Combi boilers can operate on natural gas, electricity, or LPG (liquefied petroleum gas) and use these energy sources to heat water and distribute it to the heating system. 

Working Principle of a Combi Boiler 

The working principle of combi boilers is designed to perform two main functions: heating the house and providing hot water from the taps. These functions are achieved through the harmonious operation of various components inside the combi boiler. 

Providing Hot Water 

The combi boiler ensures that water is heated immediately when a tap or shower is turned on. This process occurs in several steps. 

                    Hot Water Detection: When a tap is turned on, the flow sensor inside the boiler detects the movement of water and understands that the water needs to be heated. 

                    Ignition of the Burner: The signal from the flow sensor ignites the burner of the combi boiler. The burner produces heat by burning natural gas or another fuel. 

                    Heating the Heat Exchanger: The heat generated from the burner is transferred to a component called a heat exchanger. The heat exchanger is a network of pipes through which cold water flows. Hot gases passing around these pipes quickly heat the water. 

                   Distribution of Hot Water: The heated water is pumped towards the tap or shower. This process allows the water to be used immediately after it is heated, which is why combi boilers are also known as "instant water heaters." 

Home Heating Function 

Combi boilers provide heating by sending hot water to radiators in different rooms of the house. This process occurs automatically based on the heating demand of the home. 

                    Thermostat and Heat Sensors: The thermostat in the house constantly monitors the temperature of the rooms. When it drops below the set temperature level, the thermostat sends a signal to the boiler, and the heating process begins.

                    Circulation Pump: After the combi boiler heats the water, the circulation pump kicks in and sends the heated water to the radiators. The radiators receive this hot water and distribute the heat into the room.

                    Heat Exchange and Return: As the water heats the room through the radiators, it cools down and returns to the boiler to be reheated. This cycle continues until the desired temperature in the home is reached.

Modulation and Energy Efficiency 

Modern combi boilers are equipped with a technology called modulation. Modulation increases energy efficiency by adjusting the operating speed and power of the boiler according to the current heating needs of the house. For example, as the room temperature approaches the desired level, the boiler starts to operate at a lower power, thereby reducing fuel consumption.

Types of Combi Boilers 

Combi boilers can be categorized into different types based on their operation and energy sources. 

                    Condensing Combi Boilers: These boilers provide higher efficiency by recovering the heat from exhaust gases to heat water. Condensing combi boilers stand out with their energy-saving and environmentally friendly features.

                    Conventional Combi Boilers: Conventional boilers, which are an older technology, provide heating by directly heating the water. These types of boilers are generally less efficient compared to condensing combi boilers. [21]

                    Electric Combi Boilers: These boilers, which operate on electricity instead of natural gas or LPG, are generally preferred in areas where natural gas is not available. 


Points to Consider When Using Combi Boilers

Combi boilers require regular maintenance and careful use to operate efficiently and safely. 

                    Annual Maintenance: Combi boilers should be serviced regularly every year. This maintenance includes cleaning the burners, checking the circulation pump, and evaluating overall system performance. 

                    Ventilation: It is important that the area where the combi boiler is installed is well-ventilated. Insufficient ventilation can pose serious risks, such as carbon monoxide poisoning. 

                    Pressure Control: The water pressure in the boiler should generally be between 1-2 bar. Low or high pressure can cause the boiler to operate inefficiently and even malfunction. 

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