What is a Combi boiler?

A Combi boiler is one of the most common options you’ll encounter if you’re looking to install or upgrade your central heating system. So, what is a Combi (or combination) boiler, how do they work, and what are their key benefits?

At Ideal Heating, we’ve been a leading UK manufacturer for over 100 years, and we believe in making the complex simple. Combi boilers are the UK’s most popular heating solution, but are they the best solution for your specific home? In this guide, we will answer common questions about these models and compare them to other types of boilers on the market.

Browse all Combi boilers today.

How does a Combi boiler work?

So, how do Combi boilers heat our radiators and taps? Whenever you turn on a hot tap or switch on your thermostat, the Combi boiler detects the demand and instantly starts heating water directly from the mains. Within a few seconds, you’ll have piping hot water wherever you need it.

Because it’s under pressure already from the mains, the water flows naturally, and there’s often no need for a pump. This means that Combi boilers only heat the amount of water you need, when you need it. One of the biggest differences between Combi boilers and other models is that they don’t use a separate hot water storage tank; they provide both hot water and heating in a single appliance. As a result, they are much more energy efficient, which could mean lower utility bills for you and your family.

For more information, head to our blog, How to make your Combi boiler even more energy-efficient. 

What size Combi boiler do I need?

When it comes to finding your ideal boiler size, which is measured in kilowatts (kW) rather than feet or inches, there are several things to consider. The number of bedrooms, radiators, and bathrooms in your home will all factor into helping you choose your Combi boiler.

For a smaller property like a one-bedroom flat with 10 radiators, a 26kW Combi boiler like the compact Logic+ Combi would provide plenty of power. In a larger home where there is more demand for hot water, the stylish Vogue MAX Combi would be a better fit, it’s available in sizes up to 40kW.

Try our boiler size calculator for an expert recommendation. 

What are the advantages of Combi boilers?

The main advantage of Combi boilers is that they only heat the water you need. Unless you have a reasonably large family or use a lot of hot water, it’s inefficient to have water boiled all the time just in case you need it. That’s why Combi boilers should cost less to run than other models, as well as being more environmentally friendly.

Most people who have conventional or System boilers save money by having their heating on a timer, for example, they will set it to switch off at 11 pm and start heating at 6 am. With a Combi boiler, there’s no need to do that as hot water is available 24/7. If you get up early or come home late, you can still run a bath or have a shower.

Another benefit of Combi boilers is that they don’t take up much space. Many homes have them in the kitchen, utility room or under the stairs, and there’s no need for a separate cold or hot water tank. That’s a huge plus if you live in a flat or don’t have a loft.

If you’re installing a boiler from scratch, the Combi boiler will probably work out cheaper than other models as there’s less equipment and pipework to fit.

Learn more about the benefits of high-efficiency condensing boilers here.

Why a Combi boiler might not be for you

Combi boilers have a relatively limited flow rate. Generally, the central heating will momentarily switch off when you turn on a tap. If you turn on two hot taps simultaneously, you will notice a noticeable drop in pressure.

If you have a large family and high hot water use, such as two or more bathrooms, you may find that a large tank served by a System or Heat Only boiler will better suit your needs. Furthermore, if your Combi boiler breaks down, you lose access to hot water immediately, as there is no backup immersion heater found in a storage tank.

Is it time for an upgrade? Our guide to replacing an old boiler.

What are my other central heating options?

As a general guide, a Combi boiler will probably be the best option if you’re in a relatively small household and don’t have multiple demands on your hot water simultaneously.

As household sizes get larger, and the number of bathrooms grows, the case for a conventional or System boiler gets stronger. All types have their pros and cons, so you need to decide which one to choose based on your expected usage patterns.

Heat only boilers

A Heat only boiler (sometimes called a regular, conventional or open vent boiler) is the type of boiler that was standard in homes before the advent of the Combi boiler. It consists of a cold water storage tank, main boiler and hot water storage tank. Cold water is fed to the boiler, where it’s heated up and sent to the central heating system and the hot water tank until it’s needed.

Should you draw a bath, the hot water will need to be replaced, so you’ll have to wait for it to reheat before you can use more hot water. If several rooms all demand a small amount of hot water at the same time however, it will cope because the water has already been heated.

Read our full guide to Heat Only Boilers.

System boilers

Just like a conventional boiler, System boilers feed the central heating and the hot water storage tank, but there’s no need for a cold tank as the boiler is fed directly from the mains. They also work at higher pressure than conventional boilers.

System boilers therefore, work in the same way as conventional boilers: once the hot water in the tank is used up, you’ll need to wait for it to fill up with hot water before it can be used again.

Read our full guide to System Boilers

Reliability You Can Trust

At Ideal Heating, we are committed to quality and mutual success with our customers. Whether you are choosing a Combi, System, or Heat Only boiler, we provide the expertise to ensure you have made the right choice for the next generation.

Explore the full Ideal Heating Boiler Range. 

If you need help deciding, try our boiler selector tool or find a trusted local installer to take the next step with confidence.