Category - Boilers
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Will Scholfield, Engineer

31 Jan : Updated 18 Apr ● 6 min read

Combi boiler: Pros and cons

A combination boiler or combi boiler works differently from a standard or system boiler. It not only heats your hot water but also provides hot water for your central heating system, all within a single unit without the need for a separate hot water cylinder. 

Combi boilers deliver hot water on demand, so there's no need to wait for large amounts of water to heat up when you turn on the hot water tap. You can jump in the shower and have instant hot water!

If you're thinking about getting a combi boiler, then you're in luck. In this article, we'll explore the pros and cons of combi boilers and why they might be the ideal choice for your home.

The pros and cons of combi boilers

A combi boiler is quite different from a standard boiler, and it brings its own set of advantages and disadvantages. Let's take a closer look at the pros and cons of a combi boiler.

Advantages of a combi boiler

Combi boilers are a popular choice in the UK and are often the preferred boiler type in apartments and smaller houses, but some are now powerful enough to meet the needs of larger properties. Here are some of the advantages of a combi boiler:

Highly efficient

Combi boilers are incredibly efficient, with all new models having efficiency ratings of A. This level of energy efficiency means you can save money on your heating bills each year and reduce your home’s carbon footprint whilst you’re at it. 

They’re cheaper

Combination boilers are cost-effective due to the fact that everything is contained within one unit, boasting fewer external controls and components compared to standard or system boilers. This streamlined design can make them more affordable to both install and maintain.

Instant hot water when you need it

Running out of hot water, especially during winter, can be a nightmare. Standard or system boilers may struggle to keep up with high demand, resulting in sporadic shortages because they heat a large volume of water stored in a tank. When this tank empties, it takes time to refill and reheat the water.

However, a combi boiler never runs into this issue altogether as it does not have a hot water tank that can empty and needs to be refilled. Instead, a combination boiler can provide instant hot water by heating the water as soon as you turn on the hot water tap.


Since combination boilers stand out for their compact size, they don't need a tank to store hot water. While there are variations of combi boilers that incorporate a tank, these are typically installed in homes with higher hot water demand. However, most combi boilers are relatively small, meaning they can be installed in a typical large kitchen cupboard or rooms with limited space as long as we can maintain the clearances required by the boiler manufacturers for servicing and maintenance purposes

Easier to install

If you are swapping one combi for another the installation can be easier than a standard or system boiler. This is because a combination boiler comes without complicated components and controls that require separate installation, like a hot water cylinder and multiple controls.

Not only does this make combi boiler installation easier, but it can also cost you less.

However, converting from a standard or system boiler to a combi is more costly due to the removal and relocation of pipework. It can also be quite disruptive to your property because of pipework relocation.

To find out more, check out our user's guide to combi boilers.

Disadvantages of a combi boiler

Although combi boilers have a lot of advantages, there are also some disadvantages to keep in mind if you are considering replacing your standard or system boiler with a combi boiler:

Needs good cold water mains pressure

Most standard or system boilers use gravity to deliver water to the house. In contrast, combi boilers depend on good cold water mains pressure because water is taken directly from the mains and heated. If your home suffers from low water pressure and or flow rate, the combi boiler will not work effectively.

There are ways around this, such as investing in an accumulator to increase the water pressure in the house or contacting the local water authority for advice on upgrading your supply to potentially increase your pressure.  Both these options would entail extra costs or complexities.

Limited use

Combi boilers are limited in their use. They can only usually supply hot water to one tap at a time, so if you're running a shower while turning on another hot water tap, you will lose pressure or could suddenly find yourself experiencing a cold water shower.

Due to this limitation, combi boilers may not be the right choice for large houses with higher demands for hot water, especially when multiple people require hot water at the same time.

No immersion heater

Combi boilers do not have immersion heaters, which are commonly found in conventional boiler hot water cylinders. Consequently, if the boiler is not working, you may not have any central heating or hot water until you fix your boiler.

Is a combi boiler the right choice for you?

Combi boilers work by providing instant hot water, and although this sounds amazing, you need to consider the combi boiler pros and cons to decide whether these boilers are the right choice for you and your home.

Combi boilers are ideal for small to medium homes or apartments due to their compact size and suitability for lower hot water demands. However, they rely on good mains pressure and are limited in the amount of hot water they can provide at the same time, making them potentially less suitable for larger homes that require a large volume of hot water supply.

If you are looking into a replacement boiler for your current system, a combi boiler system is the right choice for you if:

Your hot water demands do not require an additional hot water cylinder i.e. multiple shower usage

  • You have good mains pressure
  • You do not have a power shower
  • You also need to bear in mind that the conversion from a standard or system boiler can be quite disruptive to your property

For more information on why you should change to a combi boiler, check out our useful guide.

Final Thoughts

Although the combi boiler pros and cons list is extensive, the advantages definitely outweigh the disadvantages, especially if you live in a smaller household.

These boilers provide hot water on demand, are small in size, and are easy to install and service. However, these boilers are not the perfect choice for larger homes with multiple bathrooms and or hot water outlets. 

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