What Is a Combi Boiler and How Do They Work?

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combi boiler

A combi boiler combines your hot water and heating into one. Usually starting at around €1,000, a combi boiler could be the best way in getting your energy bills down and your efficiency rating up. In our combi boiler guide, we break down the advantages and disadvantages of having one, as well as answer all your combi boiler FAQs so that you can decide if it’s the best option for your home today.

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What Is a Combi Boiler?

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A combi boiler (also known as a combination boiler or condensing boilers) provides both hot water and heating from one single unit. A combi boiler is linked to your mains water supply and the water is heated as it passes through the boiler. This allows you to have hot water as soon as you turn on the tap (or in about 20 seconds).

Combi boilers are popular for small to medium sized homes as they can meet the heating demands and don’t require large hot water cylinders and tanks. Models are available for electric and oil fired systems, as well as for natural gas and LPG.

What Are the Different Types of Combi Boilers?

We break down the different types of combi boilers below.

combi boiler
  1. Natural Gas Combi Boiler
    These are the most popular combi boilers in Ireland. Since natural gas is cheaper than electricity, oil and LPG, the running costs are lower. To have a natural gas combi boiler installed, you should consult an RGI Registered Installer.
  2. Oil Combi Boiler
    While they do exist, oil combi boilers are not very common in Ireland. They cost around 40% more than gas combi boilers to install. The running costs are also more expensive. For an oil boiler installation for your home heating, you should always consult an OFTEC Registered Installer.
  3. LPG Combi Boiler
    For homes not connected to the gas mains, LPG may be the best choice. LPG is more expensive than natural gas, but it’s still cheaper than electricity. LPG is available to purchase in both bottled supply and bulk storage. For installations, you should consult an RGI Registered Installer.
  4. Electric Combi Boiler
    Electric combi boilers use an electrical element to heat water. While these are popular for homes that don’t have access to natural gas, oil or LPG, the running costs are significantly more expensive. These boilers are only suitable for homes with limited hot water needs.

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How Much Does a Combi Boiler Cost?

The average combi boiler in Ireland costs between €1,100 and €3,000. The price you will pay for a combi boiler depends on the following various factors:

  • The brand and model of combi boiler
  • The type of boiler you’re replacing
  • Your location
  • What floor the boiler will be on
  • If you want to move your boiler to a new location
  • Any extras you would like to have (such as smart features)

In the following table, we have compiled some quotes for seven models of popular combi boilers.

Combi Boiler ModelPrice
Worcester Bosch 30kW*From €2,790
Ideal Logic 30kW*From €2,690
Glow-worm Combi 30kW*From €2,450
Ideal Logic Max**From €2,700
Ideal Logic Vogue**From €2,900
Ideal Logic Combi Boiler**From €2,600
Ideal Logic Max Combi Boiler**From €2,700

Sources: Gasworks.ie* and Completeplumbing.ie*
Last Updated: 30/11/2023

You should contact a plumber or engineer to advise you on the best option for your specific circumstances. You can also enquire to some energy providers who also offer boiler related services. For example, have a look at the Bord Gais boiler services, or contact Energia Ireland for further details.

Can I Get a Grant for a New Combi Boiler?

If you own and occupy a home that was built before 2006, you may be eligible for a boiler grant with the Sustainable Energy Authority of Ireland (SEAI). The following SEAI grants provide funding for boilers:

  • Better Energy Warmer Homes Scheme
  • Energy Efficiency Obligation Scheme (EEOS)

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How Does a Combi Boiler Installation Work?

Let’s have a look at some frequently asked questions people have regarding combi boiler installations.

Can I Install My Own Combi Boiler?

The person required to carry out the combi boiler installation depends on the type of boiler.

  1. Gas combi boiler
    A Registered Gas Installer (RGI) will need to carry out the gas combi boiler installation.
  2. LPG combi boiler
    As with a gas combi boiler, a Registered Gas Installer (RGI) will need to install the LPG combi boiler.
  3. Oil combi boiler
    An Oil Firing Technical Association (OFTEC) engineer will need to install the oil combi boiler.
  4. Electric combi boiler
    You can install the electric boiler yourself. However, it’s best to hire someone who has plumbing experience to carry out the work for you. With an electric combi boiler, an electrician will need to complete the final wiring.

Where Should a Combi Boiler Be Installed?

simple house left

Even though many companies are releasing more aesthetically pleasing boilers, most individuals still prefer to have them hidden away in their homes. The top locations to have a boiler installed include the following:

  • Utility room
  • Kitchen
  • Loft
  • Bathroom
  • Bedroom
  • Garage
  • Cupboard

How Long Does It Take To Install a Combi Boiler?

If you are swapping a combi boiler for another combi boiler, the engineer should be able to complete the installation within a day.

If the boiler you are replacing is very old or if you’re changing the boiler type, the installation will be a bit more complicated and could take more time. You will need to be around once the combi boiler has been fitted so that the engineer can show you how to use the new controls.

What Happens After My Combi Boiler Is Installed?

Most boiler installers will provide a guarantee of their services. If you have reason to believe the engineer did not safely install the boiler, follow up with them immediately. They must resolve the issue straight away or refund you the cost of hiring a new engineer.

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What Is the Most Efficient Way To Run a Combi Boiler?

combi boiler

Even if you have the most efficient combi boiler, you will still need to use it in a certain way in order for it to run at maximum efficiency. You should not keep the central heating on all the time. It’s more efficient to set the heating to come on only when you need it.

The domestic hot water, however, can be left on all the time as the combi boiler only provides hot water on demand. It can take up to 20 seconds for the water to actually get hot once you turn it on. It’s recommended to set the temperature to 75°C for central heating and to 60°C for domestic hot water.

What Temperature Should the Hot Water Be on a Combi Boiler?

ambient thermometer blue left

Combi boilers have controls that allow you to set the temperature of the water. The recommended temperature for domestic hot water is 60°C. This is the temperature that kills legionella bacteria.

Since combi boilers don’t require a water tank, it’s unlikely that legionella bacteria will develop. Therefore, it is possible to set the water temperature a bit cooler if you like. For general safety, however, the recommended minimum temperature to kill bacteria is 60°C.

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What Are the Pros and Cons of Combi Boilers?

Let’s have a look at some of the pros and cons of having a combi boiler so that you can decide if it’s worth having a combi boiler installed in your home.

Pros

  • Efficiency
  • Cheaper Than Traditional Boilers
  • Instant Hot Water
  • Compact
  • Separate Heating and Hot Water
  • Different Heating Zones
  • Controlled by an App

Cons

  • Dual Function Risks
  • Limited for Larger Homes
  • Require Strong Water Pressure
  • Complex Setup

What Are the Advantages of a Combi Boiler?

Combi boilers have many advantages. The main advantages include the following:

  • Efficiency
    They use much less energy than gas-fired boilers because they don’t have to constantly heat a hot water tank. They also run at 90%+ efficiency, thus giving them an A rating.
  • Cheaper Than Traditional Boilers
    Since combi boilers are much more efficient than older conventional models, you’re not spending as much money on wasted energy.
  • Instant Hot Water
    You don’t have to wait for the water to heat since they instantly produce hot water.
  • Compact
    They don’t require extra space to store hot water. This makes combi boilers very convenient for people living in smaller spaces.
  • Separate Heating and Hot Water
    You’ll no longer need to fire up the whole heating system to take a quick bath. This can save you quite a bit of money.
  • Different Heating Zones
    Different rooms may need to be at different temperatures at different times. Some rooms (like a spare bedroom) would rarely need heating at all. With a new digital control system, you can set up the heating to suit your home and lifestyle.
  • Controlled by an App
    Some combi boilers are compatible with heating apps, thus allowing you to control your heating and hot water remotely via your smartphone, tablet or computer.

What Are the Disadvantages of a Combi Boiler?

There are more advantages to having a combi boiler than there are disadvantages. However, depending on your situation, the disadvantages may outweigh the advantages. Let’s have a look at the cons of having a combi boiler so that you can decide if it’s worth getting one or not.

  • Dual Function Risks
    As combi boilers power both your central heating and hot water, you’ll lose access to both if the boiler malfunctions.
  • Limited for Larger Homes
    If more than one person turns on a tap in different rooms at the same time, the water pressure will significantly decrease.
  • Require Strong Water Pressure
    If your water pressure isn’t great, you should probably consider getting a different type of boiler.
  • Complex Setup
    Therefore, repairing a combi boiler is often much more expensive than repairing a conventional boiler. They also tend to require more time to fix, thus increasing the cost of labour.

Combi Boiler FAQs

Can a Combi Boiler Run Hot Water and Heating at the Same Time?

A combi boiler does not run both hot water and heating at the same time. The system will either transport the hot water to your radiators to heat your home or it will transport it directly to your tap. The system will prioritise hot water requirements over room heating requirements.

Can a Combi Boiler Run Two Showers?

Generally speaking, a combi boiler can provide water for two showers but the flow rate will be poor. Since combi boilers heat hot water on demand, ensuring that you have enough hot water for two showers is also a big request.

To have enough hot water for two simultaneous showers, you will need to have a larger combi boiler installed. Here are some general measurements to help you determine which size combi boiler would be the best option for your home:

Number of BedroomsNumber of RadiatorsNumber of BathroomsBoiler Size
Small flats and apartmentsUp to 10115-18 kW
Three to four bedroomsUp to 15118-24 kW
Larger homesOver 202 or more30 kW+
Varies1-10121-28 kW
Varies11-15229-35 kW
Varies16-213 or more36 kW+

Sources: Combi-Boilers.net, BoilerCentral.com, and DuffyHeating.ie
Last Updated: 30/11/2023

How Long Do Combi Boilers Last?

A modern combi boiler lasts for around 15 years. If you get a good quality combi boiler and regularly service it, it could potentially last you even longer.

If you get a cheaper combi boiler of lower quality, it could end up costing you more money in the long run because you may need to have it replaced sooner. For peace of mind, look into seeing if you can get the warranty extended on your boiler. Many boilers come with extended warranties of up to 10 years.

Are Combi Boilers Being Phased Out?

From next year, the installation of oil combi boilers will no longer be permitted in new builds in Ireland. From 2025, the installation of gas combi boilers in new builds will also be banned.

The services and products mentioned on this website may only represent a small selection of the options available to you. Selectra encourages you to carry out your own research and seek advice if necessary before making any decisions. We may receive commission from selected partner providers on sales of some products and/or services mentioned within this website. Our website is free to use, and the commission we receive does not affect our opinion or the information we provide.

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