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Last updated: 25th March, 2024


What Is A System Boiler?

What Is A System Boiler?

Key takeaways

  • ntegrated Components: System boilers have built-in parts like expansion vessels and pumps, making installation easier and saving space.
  • Efficiency: They are energy-efficient and compatible with solar thermal systems, offering better hot water flow rates.
  • Consistent Water Pressure: System boilers maintain a steady water pressure, providing consistent hot water even in homes with multiple bathrooms.

The best boiler for your home will be one that can meet the demands for hot water and central heating within the household.

A system boiler is one of the best for homes with a high demand for hot water because they store hot water in a separate cylinder, which gives you constant access.

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There are lots of different kinds of boilers and boiler systems out there which can make it hard for you to find the best one for your home. With the right engineer on your side, you can find an efficient boiler system that will provide hot water and central heating on demand, at a rate that is suitable for your household.

For many homes, a system boiler can be the best option, and we have written this guide to help you figure out whether this is the case for you. We are going to discuss what a system boiler is, how much they cost, as well as the pros and cons of this kind of boiler.

What Is A System Boiler?

First things first, we need to talk about what a system boiler is. This is one of the three main kinds of boiler systems that are available in the United Kingdom.

A system boiler works by directly providing heat to your central heating and hot water system through a storage cylinder. This kind of boiler works similarly to a conventional or standard boiler, as both types need to store hot water that can be used throughout the house. However, there are some key differences between the two.

Unlike regular boilers, a system boiler takes water directly from the system in your home.

This makes them a more compact system than regular boilers, while still being able to provide a high volume of hot water, making them highly versatile.

How Does A System Boiler Work?

To help you decide whether a system boiler is the right option for your home, let us take a look at how they work.

Some kinds of boiler, such as an oil boiler, require large external parts in order to provide heating and hot water. For an oil boiler, for example, an oil tank also needs to be installed along with the boiler unit to provide fuel.

However, with a system boiler, almost everything is built inside of the unit. The only external part of this kind of boiler is the hot water cylinder which holds hot water.

System boilers work by taking hot water directly from the system that is already in your home, as they are connected directly to the mains. As they have a direct connection, there is no need for a hot water tank which would have to be installed into the attic as with regular boilers.

Instead, the cylinder is a smaller unit and is used by system boilers for both hot water and central heating. These kinds of boilers can provide heating and hot water on demand for as long as the hot water cylinder is full.

The hot water cylinder does need to be refilled from time to time.

Is A System Boiler The Best Kind?

There are three main kinds of boiler systems available – system boilers, combi boilers, and regular boilers.

To help you determine whether a system boiler is the right choice for you, we need to make some comparisons between the different kinds of boilers that are available. The best kind of boiler system will be one that can provide a good level of hot water and central heating based on the demand within your household.

System Vs. Combi Boilers

Combi boilers, also known as combination boilers, combine both hot water and central heating into one unit.

As system boilers rely on a hot water cylinder, which is external, they can provide a higher volume of hot water than combi boilers. As hot water is kept on standby in an external cylinder with system boilers, they can provide more hot water than combi boilers that keep everything in one unit.

Combi boilers are great for homes with limited space, as they are compact units that have everything contained in one, whereas system boilers require external cylinders as well as the boiler unit. But this does not mean that combi boilers are free from limitations.

Without an external cylinder for hot water, which system boilers rely on, combi boilers cannot provide as much of a high demand for hot water. This can cause issues in large homes with multiple bathrooms or households that are home to a lot of people, all of which have their own demands for hot water. 

If you live in a large home with multiple bathrooms, your best bet is a system boiler instead of a combi boiler.

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System Vs. Regular Boilers

Regular boilers are known by several different names, including conventional, heat-only, or open-vetted. These are the terms to keep in mind when shopping for regular boilers, as each brand uses slightly different variations on the name.

These kinds of boilers are traditional systems, and they are usually found in older homes, so many people in the United Kingdom might have some experience with a regular boiler system.

Unlike both system and combi boilers, regular boilers are not directly connected to the water mains of your property and so do not get the water this way. Instead, for regular boilers to get water for the heating system feeder an expansion tanks also need to be installed. These are usually installed into the attic of a property.

For regular boilers to work, the feeder unit fills with cold water which it gets from the mains. This water then flows down to the boiler, with the help of gravity, as the expansion vessel keeps the level of water consistent.

An expansion vessel must also be installed along with a regular boiler and feeder as the water expands when it is heated.

The pipework that is needed for regular boilers to be installed makes the process complicated. In most cases, regular boilers are only recommended in a like-for-like replacement which means that if you already have a regular system, then getting a new regular boiler is a good idea.

A system boiler is more straightforward to install, which can make it a better option for most homes. There is less pipework required, and the installation process will be quicker, which can be a great advantage for most properties.

What Type of Home is Suited to a System Boiler?

When considering a new boiler for your home, understanding which type fits your specific needs is crucial. System boilers, known for their efficiency and capacity to meet high hot water demands, are particularly well-suited for a variety of home types. This section explores the characteristics of homes that can benefit the most from installing a system boiler, optimizing for SEO to ensure high visibility on Google rankings.

Medium to Large Sized Homes with Multiple Bathrooms

System boilers are ideal for medium to large-sized homes that have higher hot water needs, especially houses with two or more bathrooms. Unlike combi boilers, which provide hot water on demand but can struggle with multiple outlets simultaneously, system boilers store hot water in a cylinder, ensuring a steady supply even during peak usage times.

Homes with Limited Loft Space

Unlike regular boilers that require a separate cold water tank, system boilers only need a hot water cylinder, usually placed in an airing cupboard. This makes them a good choice for homes with limited or no loft space, as they don't require the additional space for a tank, making them more compact and easier to fit in smaller properties.

Homes Looking for Efficient Heating Systems

System boilers are designed for efficiency. They work by pumping hot water directly to radiators and the hot water cylinder, minimizing heat loss and maximizing heating efficiency. This makes them a suitable choice for homeowners looking to reduce their energy bills and increase their home's energy efficiency rating.

Properties with Existing Conventional Systems

For homes looking to upgrade from a conventional boiler system, a system boiler offers a straightforward transition. They can utilize the existing pipework and radiators, making the switch less disruptive and more cost-effective. This ease of integration is a significant advantage for older properties or those seeking an upgrade without extensive modifications.

Homes with a Steady Water Pressure

System boilers rely on the mains water pressure to deliver hot water. Homes with a stable and adequate mains pressure can maximize the efficiency and performance of a system boiler, ensuring that hot water is readily available when needed without fluctuations in pressure.

Eco-conscious Households

Many system boilers are compatible with solar thermal systems, making them an excellent option for eco-conscious households looking to reduce their carbon footprint and harness renewable energy sources. This compatibility allows homeowners to enjoy lower energy bills and contribute to a greener environment.


System boilers offer a versatile and efficient heating solution for a wide range of homes, particularly those with higher hot water demands, limited space for expansion tanks, or those looking to improve their energy efficiency. Understanding the specific needs of your home can guide you in choosing a system boiler that provides comfort, efficiency, and reliability. By catering to the unique characteristics of your property, a system boiler can be an excellent investment towards a more sustainable and cost-effective home heating system.

Incorporating targeted keywords such as "system boiler for home," "efficient heating systems," and "best boiler for multiple bathrooms" throughout this section helps optimize for Google SEO, ensuring that homeowners searching for reliable and efficient heating solutions can easily find and benefit from this information.

Pros Of System Boilers

System boilers combine the best parts of a regular boiler and combi boiler, giving you reliable hot water and central heating on demand.

Like a combi, system boilers get hot water directly from the mains supply, which can make them better for smaller homes as it eradicates the need for a hot water tank in the attic like traditional systems. With system boilers, hot water is stored in a separate cylinder to meet a higher demand which is why they are a great option for larger homes or those with multiple bathrooms.

There are various pros of system boilers that all homeowners should be aware of, as this can help them decide whether this is the right choice for their property.

System boilers take on the best parts of a combi boiler and a regular boiler such as:

Easy Installation

System boilers offer a simpler installation process than other kinds of boilers because they do not rely on complex pipework as regular boilers do.

In a system boiler, most of the heating and hot water compartments are installed into the unit, and the only separate part of the boiler is the hot water cylinder. The unit for this kind of boiler is compact, which makes it versatile, and is easy to install into even small spaces such as an airing cupboard.

High Hot Water Demand

System boilers are perfect for large homes or those with multiple bathrooms as they can provide a high hot water level on demand. As they rely on a separate hot water cylinder, the hot water levels provided by system boilers are higher than traditional systems making them the best for larger properties.

With the separate hot water cylinder, multiple taps can be turned on at once allowing multiple people to get bathed, take a shower, or wash the dishes at the same time without limiting the hot water access in the house.

Strong Water Pressure

Likewise, as system boilers rely on a separate hot water cylinder, they can provide a stronger water pressure than other systems.

The water used by system boilers comes directly from the mains, as opposed to a separate tank in the loft like traditional systems, the water that comes out of your taps or showers will be at a higher pressure.

Economical Running Costs

System boilers have a pump, which allows them to operate faster and run more economically than other models.

Space Saving

As system boilers do not require a separate tank or a feed, they are space-saving.

The only separate part of a system boiler is the hot water cylinder which is compact. System boilers are great for properties without a loft.


System boilers can be more efficient than other models because of the high water demand they provide. Another great factor of these boilers is the fact they can also be combined with solar-powered panels, making your home more environmentally-friendly.

The hot water cylinder can be paired with solar power to keep the temperature high, and this is a great option if you are concerned about your impact on the environment.

Best System Boilers

When selecting a system boiler for your home, it’s vital to choose a model that is reliable, efficient, and suitable for your specific needs. Top brands in the heating industry like Vaillant, Viessmann, Worcester Bosch, Alpha, and Ideal offer excellent system boilers, each with distinct features and benefits. Let’s explore these options:

Vaillant ecoTEC System Boiler Range

Vaillant's ecoTEC range, especially the ecoTEC Plus, is celebrated for its high efficiency and eco-friendliness. Ideal for a variety of home sizes due to its compact design and quiet operation, the ecoTEC Plus also boasts a high-efficiency pump, which is a boon for reducing energy consumption. It’s a top pick for medium to large homes looking for sustainable heating solutions.

Viessmann Vitodens System Range

The Viessmann Vitodens system, particularly the 200-W model, is lauded for its cutting-edge technology and exceptional energy efficiency. These boilers are equipped with a stainless steel Inox-Radial heat exchanger and a modulating MatriX cylinder burner, ensuring durability and reduced emissions. Environmentally conscious homeowners, especially in larger residences, will find this range appealing.

Worcester Bosch Greenstar System Range

Known for their reliability, the Worcester Bosch Greenstar range, including the 8000 Life model, offers high build quality and user-friendly controls. These boilers are versatile and robust, making them suitable for a wide array of homes. They also offer smart thermostat compatibility, which is a plus for tech-savvy users in modern homes.

Alpha E-Tec System Boiler Range

The Alpha E-Tec range strikes a balance between performance and affordability. With a stainless steel heat exchanger, these boilers promise efficient heat transfer and durability. Their compact size makes them ideal for smaller homes or properties with limited space, offering a high-efficiency Grundfos pump for energy savings.

Ideal Logic Plus System Boiler Range

Ideal's Logic Plus range is known for its ease of installation and maintenance. These compact, efficient boilers with a user-friendly control panel are popular among both installers and homeowners. Suitable for small to medium-sized homes, the Logic Plus range is notable for its low lift weight and comprehensive warranty.

Choosing the Right System Boiler

Selecting the appropriate system boiler involves evaluating your home's size, hot water demand, and efficiency preferences. For larger homes with higher hot water needs, robust models like the Vaillant ecoTEC Plus or Worcester Bosch Greenstar are advisable. Conversely, for smaller homes or those with budget considerations, the Alpha E-Tec or Ideal Logic Plus ranges might be more appropriate.

Energy Efficiency and Environmental Impact

Each of these boilers has unique energy efficiency ratings and environmental impacts. For instance, the Viessmann Vitodens range stands out for its low emissions, while the Vaillant ecoTEC Plus excels in reducing energy consumption. Understanding these aspects can help you make a choice that aligns with your environmental values and efficiency goals.

Smart Home Features

For those interested in integrating their heating system with smart home technology, the Worcester Bosch Greenstar range offers excellent compatibility with smart thermostats, adding convenience and potential for further energy savings.

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Frequently Asked Questions

What the difference between a system boiler and a regular boiler?

The main difference between a system boiler and a regular (conventional) boiler lies in their setup and components. A system boiler directly heats your central heating system and produces hot water for a storage cylinder. They usually contain most of the major components of the heating and hot water system built-in, making them more efficient and less space-consuming. On the other hand, regular boilers need a cold water storage tank in the loft to feed the hot water cylinder and an additional tank that maintains the water level of the central heating system.

What are the disadvantages of a system boiler?

While system boilers are efficient and suitable for high hot water demand, they have some disadvantages. They require a cylinder for storing hot water, which means they need more space compared to combi boilers. The hot water supply is limited to the size of the cylinder, and if it runs out, you have to wait for it to reheat. Also, the initial installation of a system boiler can be more complex and costly than that of a combi boiler.

Do I have a system or combi boiler?

You can determine whether you have a system or combi boiler by checking for a hot water cylinder. If you have a boiler that directly heats your water and you don't have a hot water storage cylinder, it's likely a combi boiler. If you have a hot water cylinder (usually found in an airing cupboard), but no cold water storage tank in the loft, you likely have a system boiler.

How do I know if I have a system boiler?

You likely have a system boiler if you find a hot water cylinder in your home but no water tanks in the loft. System boilers are connected to a cylinder that stores hot water, but they don’t require a cold water tank, differentiating them from regular boilers.

What are the 3 types of boilers?

The three main types of boilers are combi (combination) boilers, system boilers, and regular (conventional) boilers. Combi boilers provide hot water and heating directly from the boiler, system boilers heat your central heating system and store hot water in a cylinder, and regular boilers require both a cold water tank and a hot water cylinder.

Do I have a system or heat only boiler?

To determine if you have a system or a heat only (regular) boiler, check for a hot water cylinder and water storage tanks. A system boiler will have a hot water cylinder but no water storage tanks, while a heat only boiler will have both a hot water cylinder and water storage tanks in the loft.

Should I change regular boiler to system boiler?

Deciding to change from a regular boiler to a system boiler depends on your household’s hot water demands and space availability. If you require more efficient heating and have limited space for a cold water tank, a system boiler might be a better option. It's recommended to consult with a heating professional to assess your specific needs and the suitability of a system boiler for your home.

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Article by
Stephen Day | Co-founder
Gas Safe registered and FGAS certified engineer with over 20 years experience in the heating and cooling industry.