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How do Boilers Work

Updated: Jul 19, 2023

Boilers have played a crucial role in providing heating and hot water in residential and commercial settings for many years. Their ability to efficiently convert fuel into heat has made them a reliable choice for various applications. In this blog post, we will explore the different types of boilers and delve into their workings to shed light on their vital role in modern-day living.


What is a boiler?


A boiler is a closed vessel that generates heat through the combustion of fuel, typically natural gas, oil, or propane, to produce hot water or steam. The heat energy produced is then distributed to provide heating and hot water for various applications. Boilers are widely used in homes, industrial facilities, and commercial buildings, making them an integral part of our everyday lives.


How does a gas boiler work?


Gas boilers, also known as conventional boilers, operate on the principle of burning natural gas to heat water. The process starts with the ignition of the gas burner, which directs the flames into a combustion chamber within the boiler. As the flames heat the water-filled pipes surrounding the chamber, the water temperature rises. Hot water is then pumped through the heating system to provide warmth or to the taps to deliver hot water for domestic use.

The combustion of gas in modern boilers is highly efficient, with condensing gas boilers extracting additional heat from exhaust gases to enhance efficiency and reduce environmental impact.



How do heat-only boilers work?


Heat-only boilers, commonly known as regular or conventional boilers, are designed to work in conjunction with a separate hot water cylinder and a cold water storage tank. The cold water tank supplies water to the boiler, where it is heated and then circulated through the central heating system. The heated water is also stored in the hot water cylinder for domestic use.

Heat-only boilers are well-suited for properties with high hot water demands and existing traditional heating systems, offering a reliable and straightforward solution for heating and hot water provision.


How do combi boilers work?


Combi boilers, short for combination boilers, are a popular choice for smaller properties and

apartments due to their compact size and

efficiency. Unlike heat-only boilers, combi boilers do not require a separate hot water cylinder or cold water storage tank. Instead, they heat water directly from the mains supply on-demand.

When a hot water tap is opened, the combi boiler's internal heat exchanger quickly heats the water before delivering it to the tap. Likewise, for central heating, the boiler heats the water that circulates through the radiators without the need for a separate tank. This instantaneous hot water delivery and space-saving design have made combi boilers a preferred choice for modern households.


How do system boilers work?


System boilers, also known as sealed system boilers, operate similarly to heat-only boilers but come with an integrated expansion vessel and pump. The inclusion of these components eliminates the need for a separate cold water storage tank, making system boilers more space-efficient.

System boilers work by heating water and storing it in a hot water cylinder, ensuring a ready supply of hot water for taps and appliances. Additionally, they provide centralized heating by circulating hot water through radiators, providing consistent warmth throughout the property.



Boilers play a vital role in our day-to-day lives, providing the comfort of central heating and hot water. Understanding how different types of boilers function can help homeowners and business owners make informed decisions when selecting a heating system. Whether it's the simplicity of a heat-only boiler, the efficiency of a combi boiler, or the convenience of a system boiler, each type serves its purpose in meeting the diverse heating needs of modern living.




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