How Does a Combi Boiler Work?

Wherever you live, heat is essential to your household. It’s what keeps us warm during winter and provides us with hot water for showers and cooking daily. Most boilers are either regular or combi boilers. But what is a combi boiler? And how does it work?

In this article, we’ll be discussing combi boilers in detail—the history, the benefits, and how they work. Keep reading to learn more!

What Is a Combi Boiler?

Combi boilers are named for their function: heating your home and providing hot water. But there’s more to it than that. A combi boiler is also known as a combination boiler, because it combines the functions of a central heating system with those of an instant hot water heater. Like any other type of central heating system, combi boilers work by heating water and circulating it through pipes throughout your home. This provides heat to radiators in each room of the house. A combi boiler can also provide hot water on demand through taps in your kitchen and bathroom. In short, a combi boiler provides two primary functions in one convenient package.

How Does a Combi Boiler Work?

How a combi boiler works is a question that boggles the mind of homeowners often. A combi boiler provides hot water (and central heating) using the same fuel source. Thus, you will not need any other appliance to provide your home with either hot water or central heating. Some models even allow you to control both functions at once. For example, if you want warm water immediately, turn on the taps and tap into your instantaneous supply of warmth.

Combi boilers are also known as combination boilers because they provide high levels of efficiency. It means that this kind of boiler’s amount of heat energy can produce more heat than standard ones, given their compact and energy-saving designs.

Thus, it would be best if you did not worry that combi boilers sometimes do not have separate water tanks for hot water and central heating as it is only a matter of making use of one compact unit. This boiler type mostly contains its pump, so homeowners do not need to install a separate one.

What are the Pros n Cons of Using a Combi Boiler?

Pros of using combi boiler:

  • Reduced installation costs

Because of its compact design, it is easier to install than other heating systems.

  • Promotes fuel efficiency

Combi boilers are very efficient compared to standard models. With this boiler type, you can save up to 50 percent on your energy bills every year. They sometimes achieve 99%+ efficiency. You can also choose a combi boiler that uses renewable energy sources such as solar power or biomass to maximize environmental benefits and minimize nonrenewable sources like natural gas usage.

  • Versatile operation mode

This kind of technology allows users to use their heating system in three different modes; high-rate (boost), low-rate (economy), and auxiliary heat (standby). Thus, you can instantly control your heating system without adjusting power levels that waste energy.

  • Limited servicing cost

Combi boilers are easy to maintain because most manufacturers provide a standard one-year warranty on parts and labor. It is also easier to repair them compared with other boiler types. This means you do not have to hire an expensive technician for everyday issues or costly maintenance procedures.

  • Installation flexibility

Combi boilers are compact units, so they need less space in comparison with traditional heating systems. Thus, this kind of technology can help users save more money by avoiding unnecessary installation costs for big rooms or spaces where central heating does not work well. You will only need the right size of this unit to warm up your home effectively.

Cons of using combi boiler:

  • Higher installation cost

Combi boilers are not as cheap as other boiler types, so you will need to spend higher costs on this technology. However, it is still more affordable than oil and gas heating systems.

  • Single equipment design limits storage capacity

Since these units contain both hot water and a central heating source in one compact unit, you cannot store enough water to keep your home warm for a long time. It means when the temperature outside is lower than usual; then your heating system will run out of hot water in no time.

  • Risk of installation mistakes

Combi boilers are easy to install, but if you hire an unqualified person to do this job, they may make mistakes such as damaged equipment and flooding.

  • Single-unit design limits outdoor temperature range

Combi boilers cannot heat your home efficiently during very cold days because their heating performance ranges from +5 to -20 degrees Celsius. Thus, you need more money for a backup system (standard heating or oil/gas) to keep your home warm.

Is Combi Boiler Necessary for Every Home?

The truth is that, regardless of what any sales rep might tell you, a combi boiler system is not necessary for every home. While the hot water delivered by these systems certainly makes life more convenient, they generally don’t make sense where there are other ways to get hot water. Below are the two major factors you should consider when deciding whether or not to install a combi boiler.

1) How Far Away Is the Hot Water Heater?

A major drawback of combi boilers is that they require two separate appliances nearby. The burner sits next to the water heater, while the hot water tank must be placed somewhere nearby. Unfortunately, this means that combi systems are not always the best choice in homes with no space for two separate appliances.

For example, let’s say you have a narrow hallway between your living room and kitchen, but there will be enough space to fit one appliance. In that case, it might make more sense to install a traditional boiler system in the basement or utility room where the oil tank is located. Then, you could install an indirect water heater in the hallway. Not only would this allow you to avoid having two heating appliances in your home, but also it can be cheaper than installing a combi boiler system because there are fewer components involved.

2) How Much Hot Water Do You Need?

You should also consider your hot water usage before deciding on a heating system. For example, if several household members take long showers or like to enjoy steaming-hot baths, you might need more than one water heater for each bathroom. On the other hand, if you’re only taking quick showers and don’t mind drawing a few gallons from the tub before you get in, the need for two separate water heaters could be less apparent.

Combi systems are ideal for people who only want one heating appliance in the basement or utility room. If you fall into this category and don’t mind having your oil tank outdoors, a combi boiler is something to consider. However, if you’re not sure whether you’ll want a second hot water heater, you might consider waiting to install a heating system until this need becomes more apparent. 

In that case, the indirect water heater will likely be your best choice since it can easily adapt to meet future hot water needs. Finally, if you don’t have enough space to place two appliances and you don’t need two separate hot water heaters, you should probably look into a traditional boiler system.

There is no reason to install a combi boiler if there isn’t enough space to fit an oil tank and hot water heater near or adjacent to one another. Similarly, the only reason why you would use a combi system over a more traditional system is if you have a limited amount of space and the convenience of being able to use both appliances in one is more important to you than future expansion. In all other cases, you should consider your hot water usage and the availability of space for multiple appliances.

Can You Install a Combi Boiler by Yourself?

Installing a combi boiler is an easier and cheaper option than installing other heating systems. So yes, you can install a combi boiler by yourself. However, keep in mind that the level of difficulty varies from one model to another, so it’s important to read carefully through the manual before you start consuming your time and resources. In any case, hiring a professional for help would be a better idea because it not only ensures increased safety but also makes sure complete satisfaction with installation work.

How Much Does It Cost To Install Or Replace A Combi Boiler?

Combi boilers come in a variety of prices, and the price varies according to their features. Cost also depends on installation work, whether you want it installed by professionals or you plan to do the installation yourself. Generally, combi boiler systems start from around $500 – $600, but one must keep in mind that this is just an average mean price because some models can be much more expensive than this while others may cost less.

What is the alternative to a combi boiler?

There are several alternatives for combi boiler systems. Among them, you can take a look at the system heaters, which work similarly to combination boilers but do not provide a central heating system. Another option is to install underfloor heating. Underfloor heating provides heat by using hot water circulating through pipes installed under carpets or floorboards.


Combi boilers have many pros and cons, so you need to choose this kind of heating system carefully to avoid problems. It is a compact unit that can save up a lot of money on installation costs compared with other heating systems. Thus, you should not lose the opportunity to install a boiler that can maximize your energy savings with this type of technology.


Can you run out of hot water with a combi boiler?

The short answer is yes, but it would be very unlikely. A combi boiler heats water directly in the heating system rather than storing hot water like a traditional system. This means that, as long as there is enough water to generate hot water for the taps and showers, your heating should keep running.

Do combi boilers run all the time?

Some combi boilers do run all the time, but others are more “smart,” and they’ll turn off when not in use.

Does a combi boiler need a central heating pump?

No, a combi boiler does not need an additional central heating pump. The combi boiler acts as sort of a heat storage unit that interrupts the process of heat transfer from the hot water tank to the radiators. This allows for two sources of heated water at one time, which is great during periods when you want both your hot water and your radiator (heating) source on simultaneously.

Is a combi boiler better than a standard boiler?

It’s hard to give answers that are universally true. There are benefits of combi boilers over standard boilers, but on the whole, boiler technology is evolving quickly with even more advanced types available commercially. Every person will have different needs, so it’s best to ask a specialist before making a decision about buying one type or another. 

Can a combi boiler run 2 showers?

Answer is Yes!

A combi boiler will typically have a water heating capacity of around 40Kw, which is enough to run two showers at a time without difficulty easily. 


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