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Last updated: 16 June 2021

Combi Boilers: An In-Depth Guide

What Is a Combi Boiler?

Are you interested in installing a boiler but are unsure which type to choose? A combi (or combination) boiler is the most preferred choice of boiler systems in British households, as it provides heat both for the radiators and domestic hot water on demand. Combi boilers provide a fast and efficient supply of instant hot water since they take water directly from the mains and heat it as required.

We can help you compare combi boiler prices and quality by offering you up to four free, no obligation boiler quotes from our qualified suppliers. You simply need to fill in the contact form on the right, and our team will get in touch with you as soon as possible. This will allow you to make an informed decision and make sure that you make a wise investment. You can also take a look at our section on boiler brands, to know which is the best combi boiler on the market for you!

Combi boiler running costs are not high, as they only heat water when a hot tap or shower is turned on. In addition, there is no need to find extra space for a hot water cylinder or tank, making combi boilers an excellent space saving solution. The lack of water storage tank also means that no extra heat will be lost from a tank and then more energy used to reheat it, making combi boiler a more energy-saving option than its equivalents. 

How Does a Combi Boiler Work
Combi Boiler Features

How Does a Combi Boiler Work?

A few variations of combi boilers exist, but they all tend to work in the same way. When the temperature falls below the adjusted level, the room thermostat sends a signal to activate the boiler, and the heat will then be conducted into the central heating system. Once the required temperature has been reached, the thermostat reacts again to de-activate the combi boiler.

To supply the hot water that comes out of the taps, the cold mains water passes over a highly efficient heat exchanger. The heat exchanger transfers the vast majority of the heat from the burnt gas (approx. 90%) to the cold water and then distributes it to the taps as needed. Control valves inside the combi boiler proceed in different directions, either directing the water flow through central heating or leading it to a hot water tap – never both at the same time.

A combination boiler produces a continuous flow of hot water; however, a slight decline in water pressure may be experienced if more than one appliance is using the boiler at the same time. This makes combination boilers more suitable for smaller households, where people do not tend to use hot water simultaneously.

Pros of Combi Boilers

  • The combi boiler system is highly efficient, as it is designed to provide instant hot water as well as heating the central heating system.
  • The combination boiler system has a compact and neat looking design, making it a space-saving solution for smaller houses and flats.
  • It is very reliable and easy to install and produces hot water only on demand.
  • Since combi boilers do not have to store any hot water, there will be zero heat loss, which will help to save money on gas bills.

Cons of Combi Boilers

  • Combi boiler installation process can be tricky. There are moving parts within the boiler unit, so there is a higher risk of making errors than with a conventional boiler.
  • Combination boilers are better suited to small households, as you can only use hot water from a combi boiler system for one task at a time. Combination boilers struggle to provide hot water and heating at the same time. Therefore it might be sensible to just regulate the heating programmer accordingly.
  • A problem might occur when the combi boiler breaks down. Then, quite frankly, you will have no other water heating application than the kettle. However, most of the conventional boilers are equipped with an electronic immersion heater, thus even when the boiler fails to work, you are still able to use hot water.

How Much Will a Combi Boiler Cost?

For best results, it is recommended to buy a brand new combi boiler from a respected retailer or manufacturer. Although new boilers are more costly than for example second-hand equipment, they are guaranteed to last for a longer period. In addition, further repairs are often included in your warranty.

The cost of the combination boiler depends on two main elements. Firstly, the size of the household—the more bedrooms and bathrooms you have, the bigger and more expensive boiler you will probably need. For instance, a small combi boiler is suitable for max. 1 bathroom and 3 bedrooms and will cost around £500-800. A medium-sized combi boiler costs slightly more—between £1,200 and £2,000. Another thing to consider is the quality of the model you choose. Prices differ according to the quality, efficiency, and durability of the branded products: get the best combi boiler deals on Greenmatch!

Combi Boilers


Is a combi boiler the right choice for me?

Combination boilers perform to a high level at a reasonable cost, which is also a reason why they account for well over half of all the new domestic boiler installations in Britain every year. It is more appropriate for smaller houses and flats with a shower solution, rather than for large households with several bathrooms since a slight decline in water pressure might occur if more than one appliance is using the boiler at the same time.

Which combi boiler should I choose?

Combi boilers come in different styles and sizes. It depends whether you are looking for a more economical solution, or plan to invest in an eco-efficient model to benefit from lower heating bills in the long run. You should make sure to pick your boiler in the right size, as it can have a remarkable effect on your heating bills.  Further, think carefully how efficient you need your boiler to be. Boilers are rated on an efficiency scale, ranging from A to G, where A stands for the most energy efficient type of boiler.

Are combi boilers more costly compared to other types of boilers?

New boilers are not cheap and prices range depending on the brands and types of boilers available. Boiler prices normally vary from close to £500 all the way to £2,500, so it is necessary to collect all the facts before making the investment. Combi boilers are expected to cost anything from £500 up to £2,000.

Do all types of showers work with combi boilers?

Most of the standard shower installations are compatible with a combination boiler, however, pump assisted showers require tank fed boiler systems. Combi boilers might not be suitable for modern multi-jet showers, which demand higher water pressure than a combi boiler can provide.

Do combi boilers provide good water pressure?

The water is supplied from the mains; therefore the water pressure is generally good. However, the flow can be limited if several appliances are using hot water at the same time. If you have more than one bathroom, a traditional system boiler might be a more suitable option. Larger combi boiler models are generally better at combatting any decline in performance due to the strain on the system.

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