Found in over 80% of homes in the UK, the gas central heating boiler is still something of an enigma to many users. It produces hot water and heats our homes but few people really know how a boiler works. While it’s not essential to know, it can be useful to understand what’s gone wrong if your boiler suddenly breaks down.

How a boiler works central heating guide© Daisy Daisy / Shutterstock.com

Gas central heating boiler construction

The basic principle of a boiler is to transfer heat to water. In essence, your boiler works by heating up water that is then pumped around your home.

This is only a very simplistic view of what a boiler is. To understand how a boiler works we need to begin looking at the construction of a gas central heating boiler.

In terms of design and function, a gas boiler works in a very similar way to other types of heating. The difference is that fuel gas is highly flammable and a number of important safety features are included for your protection.

Inside a gas boiler

To understand how a boiler works we need to look at the various key components that you’ll find inside a gas heater:

  • Gas burner: This generates the heat which is used to warm your home.
  • Heat exchanger: A device that is used to transfer heat between a solid object and fluid.
  • Control technology: Used to control the function of your gas heating system.
  • Diaphragm expansion vessel: Diaphragm tanks are pressurised water vessels which allows the water to expand and absorb pressure surges that happen during heating.
  • Exhaust pipe: Often a thin plastic pipe that is pulled through the chimney to remove traces of carbon monoxide that is produced as a by-product of the gas boiler heating process.

Gas heating systems with additional water heating

Although we have covered many of the basic elements inside a gas heating system, there are variants. If a heating system also provides hot water then an additional hot water storage tank is required. 

In most cases an exception can be made for wall-mounted gas boilers that are able to provide hot water on demand.

How a gas boiler works to create heat

A gas boiler functions in a similar way to oil or biomass boilers, with the central element being the burner; this is switched on and off by a heating control. You can either trigger the switch manually or by setting the thermostat to react when the temperature drops below a certain level.

A Piezo ignition, ignites for a period of one to two seconds and then after around one second the gas line opens allowing for an outflow of gas. The delay of opening the gas supply is highly important in gas heating as it prevents the influx of large amounts of gas that if ignited too late could cause an explosion.

The burner is connected to a heat exchanger that heats water in its chamber, the hot water is then pumped in the direction of the heating circuit.

Even though it plays no part in the creation of heat, the heart of gas heating boiler is the control technology. This is responsible for the efficient and trouble-free operation of the system. It also ensures communication between indoor or outdoor temperature sensors and the boiler.

How other types of boilers work

As mentioned previously there are other types of boilers available on the market. How a boiler works for one fuel type can differ from another, but often the principles remain the same.

Looking to replace your gas boiler?

How oil boilers work

Oil boilers perform in a very similar way to gas boilers, converting oil fuel into heat within the combustion chamber, which heats up the heat exchanger, finally heating the water.

The difference between the two fuel types is how the fuel is managed. Oil boilers require a storage tank that is usually found in the back yard or garden. The oil is delivered by a tanker and stored until it’s used. Oil boilers are less eco-friendly than gas boilers. Often you’ll find oil boilers used in the countryside where no gas pipeline is present.

Electric boilers

Similar to oil boilers, electric boilers are often found where there is no access to a gas line. But unlike oil and gas boilers, electric boilers don’t use a solid fuel; instead they transfer energy to heating elements to heat up the water.

While electric boilers ‘burn’ cleaner, they are not as efficient and are more expensive than oil or gas boilers.

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