Essentially, a boiler is like a big furnace or fire that’s controlled by your thermostat. The main function of a gas boiler is to act as a heater and provide buildings with the hot water they need, which is important for two very big reasons.

Firstly, the hot water produced by your boiler is pumped through your radiators when you turn on your central heating, providing them with a reliable source of heat. This keeps you warm and comfortable in the colder months of autumn and winter — and sometimes during spring and summer as well.

The second main function is providing a steady supply of hot water for your sinks, baths and showers. They do this by heating up a tank or container of water and keeping it at a consistent temperature, which means you can rely on the hot water you need to keep yourself (and your belongings) sparkling clean.

While there are a variety of gas boilers on the market, they all work in much the same way — by heating gas to warm your home. This gas can enter the boiler via two different methods: by being connected to a main or through an LPG bottle.

The hot water produced by your gas boiler is then pumped through your central heating system, travelling via pipes into your radiators to heat your home. Depending on the type of boiler you own, this will either flow directly through taps and showers (combi), or will be transferred and stored in a separate water tank or cylinder (system and heat only).

Central heating works like a circuit – hot water is pumped from the boiler into each radiator in turn, and is in constant, or near-constant, circulation when the heating is switched on. Although you might need to top up the pressure in your radiators from time to time, the same water is used over and over again.

By the time the water has passed through all the radiators, it will have lost some of its heat, but that is restored in the boiler and it is sent around again.

Whether or not central heating is “on” is determined by the thermostat, which helps the temperature of a home stay more or less constant, to within a few degrees either side of your chosen temperature.

The second job of the gas boiler is to heat water. It performs this task in the same way as it does for central heating, that is, through pumping circulated water over the flame so it heats up.

There are two ways it does this:

In both cases, however, the water that is heated over the flame is not the water that comes out of the tap – it is simply used as a medium for heating the water you use.

There are numerous components housed inside a gas boiler, including a gas burner, heat exchanger and a flue. Each element serves a specific purpose, working together to keep your home warm and provide you with a continuous, reliable supply of hot water.

Below are the main individual components, along with the functions they fulfil:

Although it’s gas that heats the water in our boilers and keeps our homes warm, gas boilers actually do need a small amount of electricity to work too. That may sound strange, but electricity is simply used to help specific parts and mechanisms of our central heating systems function.

Electricity is used to power everything from the valve that opens to let gas flow into the combustion chamber, all the way to digital displays and smart thermostats

Combi boilers are suitable for most small and average-sized households. They work by circulating hot water around the central heating system, and also heat up incoming mains water incredibly quickly when a hot tap is turned on. That means instant hot water, 24/7. They don't require storage tanks either, which means they take up hardly any space.

A potential drawback is that if several people turn on different hot taps or showers at the same time, pressure and temperature of the water will drop as the heating capacity is exceeded. Also, since they rely on water mains pressure, they are unsuitable for areas of low pressure.

How long a gas boiler lasts depends on how well it’s cared for, but it’s generally best to replace it every 15 years. It’s not that they’ll suddenly stop working at this age, but this is the point where it becomes more cost effective to invest in a new model.

Gas boilers are complicated appliances that work around the clock to make sure we have hot water and heating, whenever we may need them. They work so hard to keep us comfortable that even the most reliable boiler parts will eventually fail.

There are several signs to be aware of that may signal your trusty gas boiler is reaching the end of the road. It may be regularly breaking down or losing pressure, or you may notice unusual loud bangs coming from your central heating.

If your gas bills start to creep up unexpectedly, that’s another sign that your boiler is not operating efficiently. In all of these cases, we’d recommend calling out a Gas Safe engineer to cast an expert eye over it. It could be that there’s a simple solution, or they may advise you it’s time to invest in a new model.

Our faithful gas boilers can’t last forever, but there are steps we can take to look after and keep them working as efficiently as possible. Annual services performed by a Gas Safe accredited engineer will include essential safety checks and ensure all of its parts are working as they should.

Other top tips for keeping your gas boiler healthy are running it for around 15 minutes even in the summer months. It’s also good practice to keep an eye on your boiler’s pressure to make sure it doesn’t get too low, and try bleeding your radiators if they seem cooler at the bottom.

Not only will your gas boiler last longer if you take good care of it, that extra efficiency will also mean your utility bills stay lower. It will also benefit the environment, as it won’t need to work quite so hard to keep your home warm.

The short answer is yes. Modern gas boilers have been created with technology that has specifically been designed to keep you, your family and your home safe. This is thanks to the development of new safety features, including a sealed or balanced flue.

Older models were typically constructed with an open flue or chimney. These systems worked by drawing in carbon dioxide from the room, the gas was then combusted, and wasted products were ejected outside. However, an open flue can be subject to a range of issues, including blockage.

When a flue becomes obstructed, this can cause the boiler to release carbon monoxide into the home, which is a colourless, odourless and tasteless gas. High levels of carbon monoxide can have negative impacts on health — take a look at our blog post protect your family from CO for more information.

Today, modern gas boilers are manufactured with a balanced or sealed flue. Connecting your boiler to the exterior of your home, this type of flue works by drawing in carbon dioxide from outside, heating and then drawing the waste back out. Unlike an open flue, the air inside your boiler is sealed off from the room where it’s housed, meaning toxic gases are unable to escape.

You may have heard the government is planning to introduce new legislation around the future of heating systems in the UK. The Future Homes Standard will include new rules for new build homes, which means they’ll use alternatives to gas for their heating systems beginning in 2025.

This certainly doesn’t mean that gas boilers will disappear or be banned, as the legislation only applies to new build homes. There’ll still be many efficient gas boilers continuing to heat homes and workplaces in 2025 and beyond, working alongside alternative heating systems to lower carbon emissions for all of us.