May 31, 2021

The traditional gas boiler has discreetly been at the centre of most British homes for half a decade, if the kitchen is the heart of a home, then most certainly the gas boiler is the engine that makes it all work.

They’re often neglected, many times are taken for granted but always missed when they breakdown, the gas boiler, Heatsy salutes you.

For 50 years you’ve kept us and our families warm, protecting us from the cold winters, and gifted us with warm water to bathe and relax after a hard day at the office.

There are generally three main types of gas boiler, Heat Only boiler, System Boiler, and Combi Boiler.

Heat Only Boiler

The Heat Only boiler is the oldest type of boiler, it’s a very simple appliance and generally consists of little more than a gas valve, a burner, and a heat exchanger.

It will be installed with a hot water cylinder, and you’ll usually have two water cisterns in the loft.

System Boiler

The system boiler is a natural progression from the heat only boiler, it’s a lot more sophisticated incorporating many more safety features as well as many of the external parts from the heating system - hence the name, system boiler.

Combi Boiler

The combi boiler is the most popular boiler in the UK, and with good reason.

Being a small island space has always a point of contention in big cities and big bulky hot water cylinders took up far too much of the limited space available in many flats. Enter the combi boiler, with the ability to provide heat for your central heating and instant hot water for your taps there was no longer a need for the hot water cylinder, and we’ve loved them for the last 25 years.

If you’d like a more in-depth explanation of the different types of gas boilers and how they work, read our blog post - What type of boiler do I have?

Now we have a basic understanding of the different types of boilers, we can look at how the magic happens and see how boilers work.

The basic chemistry of how the gas boiler works is very simple:


In our case the fuel is natural gas, the heat comes from an ignition source the oxygen that starts the combustion process comes from the air and the stored energy in the fuel is released as heat.

The heat is transferred through the boiler’s heat exchanger to water which is then distributed by either a pump or gravity throughout the heating system and passed to heat emitters.

For a more scientific analysis of combustion and the complete process of heating your home, look at our blog post - How Your Gas Boiler Works.

Given the importance of the gas boiler in our everyday lives and the potential dangers from gas and CO leaks, it’s not surprising that both the HSE and boiler manufacturers suggest that your gas boiler should be serviced at least once every twelve months.

An annual boiler service is essential maintenance, and vital to ensure your trusted gas boiler continues to operate at its optimum efficiency and to prevent any dangerous CO leaks or costly boiler breakdowns.

To see the checks, we do and the process we follow when servicing your gas boiler visit our Annual Boiler Service page.

There is a common misconception that modern condensing gas boilers are unreliable and don’t last as long as older boilers.

The truth is that the majority of gas boilers breakdown because of poor installation and maintenance, given that your boiler regularly endures flames burning up to 1950 degrees Celsius we think it manages just fine.

Of course, boilers do breakdown even when they’re maintained perfectly and looked after lovingly.

If you need your boiler repaired or you’d like to read more about boiler repairs and how we can help you visit our Boiler Repairs page.

Unfortunately, they don’t last forever, and the day will come when you’ll need a new boiler installation.

Installing a gas boiler is not like fitting a washing machine, it’s a complex piece of building engineering and should only be completed by a competent professional who’s registered on the Gas Safe Register.

A properly installed gas boiler and heating system require complex calculations such as heat loss, pump sizing, and pipe sizing to make sure the installation is correctly specified for your home which will in turn save you money on your energy bills and reduce the risk of unnecessary boiler break downs.

To see which appliances, we recommend and how we install them visit our Boiler Installation page

We hope you enjoyed reading our brief overview of what a gas boiler is and how it works and that you’re intrigued enough to read our more in-depth pieces that go into far more detail.

But for now, we’re happy that hopefully, next time your trusted boiler breaks down or your annual service reminder pops up in your inbox you’ll be a little more forgiving.

We hope you found this article interesting and useful, if you didn’t please let us know why and what we could do to improve it.

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Please remember, we’re heating experts so if you need your boiler repaired, a new heating installation or if you’re struggling with anything we’ve discussed here feel free to get in touch with us now so we can see how our solutions might help you.

Thank you for reading.