Combi Boiler: The Ultimate Guide

combi boiler

Thinking about having a combi boiler installed? 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.


What is a combi boiler?

A combi boiler (also known as a combination boiler) 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.

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Types of combi boilers

We break down the different types of combi boilers below.

combi boiler
  • 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.

  • 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, you should always consult an OFTEC Registered Installer.

  • 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.

  • Electric combi boilerElectric 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.

Combi boiler price: How much does it cost to have one installed?

The average combi boiler in Ireland costs between €500 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 three types of popular combi boilers.

Combi boiler type Price
Worcester Bosch 30kW €2,590
Ideal Logic 30kW €2,370
Glow-worm Combi 30kW €2,370

Source: Gasworks.ie

You should contact a plumber or engineer to advise you on the best option for your specific circumstances.

Energy bills too high? Selectra can help!Our free service can get you a better deal in minutes. Call one of our trained advisers today to find out how much you could save. Call 1800 816 036 or get a free callback now.

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
  • Warmth and Wellbeing Scheme
  • Energy Efficiency Obligation Scheme (EEOS)

For more information, head to our complete guide on SEAI grants for homeowners.

Combi boiler installation

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.

  • Gas combi boiler — A Registered Gas Installer (RGI) will need to carry out the gas combi boiler installation.
  • LPG combi boiler — As with a gas combi boiler, a Registered Gas Installer (RGI) will need to install the LPG combi boiler.
  • Oil combi boiler — An Oil Firing Technical Association (OFTEC) engineer will need to install the oil combi boiler.
  • 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?

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. If you hired a

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 at 75°C for central heating and at 60°C for domestic hot water.

Want information on how to be more energy efficient? Check out our 101 tips on ways to save energy and reduce your bills.

What temperature should the hot water be on a combi boiler?

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.

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.

What are the advantages of a combi boiler?

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

  • Combi boilers are very efficient. 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.

  • They’re less expensive to run than traditional boilers. Since combi boilers are much more efficient than older conventional models, you’re not spending as much money on wasted energy.

  • They heat water immediately. You don’t have to wait for the water to heat since they instantly produce hot water.

  • They’re very compact. They don’t require extra space to store hot water. This makes combi boilers very convenient for people living in smaller spaces.

  • Heating and hot water are controlled separately. 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.

  • You can set up 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.

  • You can control the heating and hot water via 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.

  • If it breaks down, you lose both hot water and central heating. As combi boilers power both your central heating and hot water, you’ll lose access to both if the boiler malfunctions.

  • They can’t meet the high water demand of large homes. If more than one person turns on a tap in different rooms at the same time, the water pressure will significantly decrease.

  • They require strong water pressure. If your water pressure isn’t great, you should probably consider getting a different type of boiler.

  • They have a very complex set-up. 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

Below, we answer some frequently asked questions that people have about combi boilers.

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. In the following table, we have provided some general measurements to help you determine which size combi boiler would be the best option for your home.

Number of bedrooms Number of radiators Number of bathrooms Boiler size
One to three Up to 10 One 24kw to 27kw
Two to four Up to 15 Two 28kw to 34kw
Three to five Up to 20 Two 35kw to 42k

Source: Mr Central Heating

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.

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