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Last updated: 13th November, 2023


What is a Storage Combi Boiler?

What is a Storage Combi Boiler?

Key takeaways

  • Storage combi boilers combine central heating and hot water with an internal hot water cylinder for higher demand.
  • These boilers draw water from the mains, providing instant hot water without sacrificing water pressure.
  • They offer a compact solution suitable for a range of property sizes, from small flats to large houses.

Storage combi boilers are a popular choice for homeowners who want the benefits of a combi boiler with the added advantage of hot water storage. Our guide explores the key features and benefits of storage combi boilers, including their space-saving design, energy efficiency, and fast hot water delivery.

A storage combi boiler is a modern and efficient alternative to regular combi boilers, offering both central heating and hot water capabilities – but with a notable difference. 

These innovative boilers incorporate an internal hot water cylinder, which means they can meet higher demands for hot water, providing a better solution for homes with multiple bathrooms or larger families.

The key to a storage combi boiler's operation lies in its ability to draw water from the mains supply, heat it up, and deliver instant hot water without compromising on water pressure. 

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This is achieved through a combination of a primary heat exchanger, responsible for heating water as it passes through pipes to radiators, and a secondary plate heat exchanger that ensures clean hot water reaches taps and showers.

Unlike regular combi boilers, storage combi boilers offer increased hot water storage capacity within their compact form, providing the best of both worlds. This versatility allows them to meet the needs of various properties, ranging from small flats to large houses, while providing efficiency and convenience to homeowners.

What Is a Storage Combi Boiler?

A storage combi boiler is a type of boiler that combines the benefits of a traditional combi boiler with an internal hot water cylinder, making it suitable for higher hot water demands. 

Drawing water directly from the mains supply, it heats water instantly and stores a portion of it in the integrated cylinder for later use. This ingenious design enables the boiler to supply hot water instantly to different parts of a household without affecting the flow rate.

Unlike a standard combi boiler, a storage combi boiler has an integrated thermal water store within the boiler unit, so there is no need for an external hot water tank. This compact design makes it suitable for smaller homes and flats where space is limited. Furthermore, it retains the functionality of producing and delivering pressurised hot water, similar to a system boiler with a hot water cylinder.

Essentially, a storage combi boiler brings together the best of both worlds, providing homeowners with a reliable source of hot water while saving valuable space. 

This innovative solution is particularly attractive to those with higher hot water requirements, as it can cater to multiple hot water outlets simultaneously without impacting the water flow rate.

In summary, storage combi boilers offer a practical and efficient alternative to traditional combi or system boilers. By combining an internal hot water cylinder within the boiler unit, they ensure a more constant flow of hot water to meet higher demands, without compromising on space or efficiency.

How Does A Storage Combi Boiler Work?

A storage combi boiler cleverly combines features of both combi boilers and system boilers. It is designed to provide hot water on demand while also storing a certain amount of water for instant use in its integrated hot water cylinder.

Heating water in a storage combi boiler is achieved through the use of heat exchangers. Cold water from the mains supply passes through these heat exchangers, which are typically warmed by either the boiler's gas burner or an electric heating element. This process ensures a consistent supply of hot water whenever needed.

In addition to the heat exchangers, storage combi boilers utilise a cylinder loading system. This technology allows the boiler to heat and store a substantial volume of water in its internal cylinder, ready for immediate use. 

This feature comes in particularly handy during periods of high hot water demand, as it ensures that multiple outlets can be supplied with hot water simultaneously without affecting the flow rate.

While operating in a similar fashion to regular combi boilers in terms of providing central heating, storage combi boilers distinguish themselves with their ability to address higher hot water demand. The integrated hot water cylinder ensures that there is a readily available supply of hot water, even when multiple taps or showers are in use.

Storage combi boilers are highly energy-efficient, as they only heat the water that is actually needed for use. This, in turn, means a reduction in energy consumption and, as a result, lower energy bills. Furthermore, their compact size allows them to fit comfortably in smaller homes or flats, providing the advantages of both combi boilers and system boilers within a single unit.

In summary, by combining efficient heating, hot water on demand, and the convenience of a hot water cylinder, storage combi boilers offer a versatile and efficient solution for homeowners seeking both space-saving design and reliable performance.

Difference between a Storage Combi and a Regular Combi

A storage combi boiler is a combination boiler that also contains an internal hot water cylinder. This additional feature allows storage combi boilers to cater to higher hot water demands, making them suitable for larger homes with multiple bathrooms. 

On the other hand, a regular combi boiler, which is the more common type, provides heating and hot water directly from a single unit, but without any internal storage.

Due to the storage combi's internal hot water cylinder, it can supply more immediate hot water compared to a regular combi. In contrast, a regular combi boiler relies on the mains water supply, which can sometimes result in homeowners having to wait for hot water. 

However, when it comes to storage combi boilers, they draw water from the mains supply too, ensuring an almost constant availability of hot water.

Another notable difference is the installation process. Storage combi boilers are larger and may require more space, but they eliminate the need for a separate cold water storage tank or an external hot water cylinder. 

Regular combi boilers, on the other hand, are compact and easy to install, with no required additional storage.

In terms of energy efficiency, a storage combi boiler might have a slight advantage. It heats and stores hot water only when needed, thus reducing energy wastage from heat loss in an unused hot water cylinder. On the contrary, a regular combi boiler heats water on-demand, which might lead to energy loss if multiple hot water taps are running simultaneously.

It's essential to select the right type of combi boiler to suit your home's particular needs. Storage combi boilers are more suitable for larger properties with higher hot water consumption, while regular combi boilers are recommended for smaller households with fewer hot water requirements.

Understanding The Mechanism

A storage combi boiler is an innovative heating system that combines the benefits of a combi boiler with the added advantage of an internal hot water cylinder. 

This unique feature allows the boiler to meet higher demands for hot water compared to traditional combi boilers, making it suitable for households with increased hot water needs.

The internal cylinder within a storage combi boiler ensures a sufficient supply of hot water while the heating system works alongside it. As water is drawn from the mains, it passes through the primary heat exchanger, which generates heat by transferring energy from the burning fuel to the water. This heated water then circulates through the pipes and heats the radiators in your home.

When there is a demand for hot water, such as when a tap or shower is switched on, the boiler utilises its secondary plate heat exchanger. This ensures that the hot water reaching the taps is clean and free from contaminants. 

The internal hot water cylinder plays a significant role here by storing a portion of the heated water, enabling the storage combi boiler to deliver a consistent flow rate with minimal drop in pressure.

A thermostat regulates the temperature within the storage combi boiler, maintaining a comfortable, energy-efficient environment for your home. If the thermostat senses that the temperature has dropped below the set level, it will signal the boiler to ignite and increase its heating output.

Notably, storage combi boilers require minimal space due to the integrated hot water tank, making them suitable for small flats and homes. Their compact nature allows for a more straightforward installation process compared to separate systems.

In summary, storage combi boilers efficiently manage the heating and hot water needs of a household by combining the convenience of a combi boiler with the increased capacity of an internal hot water cylinder. 

This innovative design ensures a consistent flow rate and clean hot water supply, regulated by a thermostat for energy efficiency and comfort.

Varieties of Storage Combi Boilers

When it comes to storage combi boilers, there are various models available to cater to the diverse needs of homeowners. One popular model is the Vitodens 111-W. This high-performance wall-mounted storage combi boiler is designed to provide rapid, reliable hot water supply along with energy-efficient central heating. Its compact size makes it suitable for homes with limited space, while its innovative technology ensures high efficiency and low energy costs.

Another notable option is the Vitodens 222-F. This floor-standing storage combi boiler offers a higher hot water output than the 111-W model, making it an excellent choice for homes with higher hot water demands. Its energy efficiency and modern design complement its superior performance, rendering it a top choice in the world of storage combi boilers.

Storage combi boilers, as the name suggests, combine the benefits of combi boilers and system boilers. They draw cold water directly from the mains supply, heat the water on demand, and store a supply of hot water in an efficient thermal store. This unique combination offers several advantages over traditional combi and system boilers.

In contrast to storage combi boilers, system boilers require a separate hot water cylinder to store and deliver hot water. This can take up additional space and make installation more complex. Regular boilers, on the other hand, utilise a cold-water storage tank along with a hot water cylinder, resulting in a bulky and less efficient system.

To recap, storage combi boilers such as the Vitodens 111-W and Vitodens 222-F offer a high level of efficiency and convenience for homeowners. These models save space, provide instant hot water, and deliver impressive performance for various household needs. Therefore, they prove to be an astute choice for those looking to upgrade their existing heating systems or install a new one.

Space and Installation Requirements

Storage combi boilers are an excellent choice for households with limited space. Due to their compact size, they can easily fit into small areas, such as kitchen cupboards or airing cupboards. Typically, these boilers come in two main forms: wall-mounted and floor-standing units.

Wall-mounted storage combi boilers are popular in the UK because they require little space for installation. As the name suggests, these units are mounted on a wall, thus freeing up valuable floor space. This type of boiler is particularly suitable for smaller homes or flats, where space might be at a premium.

Floor-standing units, on the other hand, are slightly larger and sit on the floor. They still occupy less space than traditional combi boilers and system boilers with separate cylinders. However, they might not fit into the smallest of cupboards. 

Despite their size, floor-standing storage combi boilers are often an ideal choice for homes with limited airing cupboard space.

Installation of a storage combi boiler needs careful consideration, particularly when connecting to the mains water supply. A qualified engineer should perform the installation to ensure the boiler is working efficiently and safely. This will also help to avoid any potential issues with water pressure and flow rate.

In conclusion, storage combi boilers offer an effective solution for homes with limited space, such as those in the UK. Both wall-mounted and floor-standing units can be installed easily in small areas, like kitchen and airing cupboards. Regardless of the chosen type, a proper installation by a competent engineer is essential to guarantee safety and efficiency in operation.

Suitability Based on Hot Water Demand

A storage combi boiler is an ideal solution for households with high hot water demand. Unlike a standard combi boiler, which heats cold water directly from the mains supply, a storage combi boiler has an internal hot water cylinder, allowing it to meet higher demand for hot water.

In situations where multiple outlets require hot water simultaneously, storage combi boilers excel. Their design enables the provision of hot water for various tasks, such as taking multiple showers or filling a bathtub whilst doing the dishes or washing laundry. Homes with multiple bathrooms or larger families often benefit significantly from the efficient hot water supply of a storage combi boiler.

Another advantage of storage combi boilers is that they provide instant hot water, much like their combi counterparts. This feature eliminates the need to wait for the water to heat up, saving time and energy in the process. Furthermore, these boilers are compact, often similar in size to a standard combi boiler, making them a perfect choice for smaller properties with limited space.

In conclusion, a storage combi boiler is a suitable choice for households with high hot water demand and multiple outlets. Their efficiency, compact size, and built-in hot water storage make them a practical solution for those seeking a reliable and convenient solution to their hot water needs.

Storage Combi Boiler Vs. Regular and System Boilers

A storage combi boiler, as the name suggests, combines the benefits of a regular boiler and a system boiler by incorporating an internal hot water cylinder. This enables it to meet high hot water demands while saving space in smaller homes.

Regular boilers, also known as heat-only boilers, require a separate hot water cylinder and a cold-water storage tank, typically installed in the loft. These systems are more suitable for larger homes that have multiple bathrooms and high hot water demands, as they can supply hot water to many outlets simultaneously. Although they occupy more space, regular boilers are an excellent choice for homes with an existing central heating system, as they can be easily replaced without additional piping or equipment.

On the other hand, system boilers need a dedicated cylinder to store hot water, but not a cold-water tank. They heat water directly from the mains, which eliminates the need for a separate hot water cylinder, making them more space-efficient than regular boilers. However, compared to storage combi boilers, they may not be as effective in meeting high hot water demands in smaller homes.

Storage combi boilers are an ideal choice for those who want a compact solution for their central heating and hot water needs. It not only provides instant hot water but also has the added advantage of an internal hot water cylinder, ensuring a more robust hot water supply.

In summary, the choice between a storage combi boiler, regular boiler, or system boiler depends on the specific needs of your home. Factors such as space, hot water demand, and the existing central heating installation will influence the decision.

Identifying The Best Brands and Models

When selecting a storage combi boiler, it's essential to explore various brands and models. Recognised for their efficiency and effectiveness, storage combi boilers merge the benefits of combi boilers with the addition of internal hot water cylinders to meet higher hot water demands.

One notable brand worth considering is Viessmann. Their Vitodens 111-W B1LD-35 Storage Combi Boiler is particularly powerful and popular among homeowners. It's ideal for those in need of a robust boiler system that can handle the demands of multiple bathrooms or larger properties.

Worcester Bosch is another reputable brand in the industry. Their Combi Greenstar 4000 stands out as an excellent choice for small homes, emphasising energy efficiency and space-saving design.

For those needing an LPG compatible option, the Vitodens 222-F also produced by Viessmann, is a great choice. This boiler is designed to work seamlessly with LPG systems, providing a flexible and reliable heating source for homes not connected to the mains gas network.

When evaluating storage combi boilers, it's crucial to consider the number of radiators it will need to support. Boilers with higher capacities can handle more radiators while maintaining a steady flow of hot water. Both Viessmann and Worcester Bosch offer models with varying output capacities, catering to diverse household requirements. It's crucial to select the appropriate model based on the size and specific needs of your property.

In conclusion, the Viessmann Vitodens 111-W B1LD-35, Vitodens 222-F, and Worcester Bosch Combi Greenstar 4000 are all prime examples of reputable storage combi boilers on the market. By carefully considering the brand, LPG compatibility, radiator capacity, and features, homeowners can confidently choose the best storage combi boiler to suit their individual needs.

Factors to Consider When Choosing a Storage Combi Boiler

When deciding on a storage combi boiler, numerous factors come into play. Firstly, consider your budget. Storage combi boilers can be a pricey investment – their cost generally exceeds that of regular combi boilers due to the additional technology and integrated cylinder. However, the benefits may outweigh the initial outlay.

In households requiring a steady flow of hot water to multiple bathrooms and radiators, storage combi boilers are an ideal solution. They draw water from the mains supply, heating it instantly, while storing some hot water in the cylinder. This capacity allows the boiler to supply water to different parts of the home without affecting the flow rate.

To ensure maximum efficiency, it's crucial to choose the right boiler suited to your household's specific needs. Factors such as the number of radiators, heat exchangers, and the cylinder size come into play. Smaller flats or houses generally have room for a storage combi boiler, providing the advantages of a system boiler without the bulk.

In terms of technology, modern storage combi boilers come with energy-saving features that can reduce monthly bills and provide a greener heating method. Look for models with high efficiency ratings and certifications to make a worthwhile long-term investment.

Finally, when comparing various boiler types, take note of the manufacturer's warranty. A lengthy warranty can offer peace of mind, knowing that repair costs, if any, will be covered by the manufacturer in case of issues or malfunctions. So, selecting a reputable and reliable brand is of paramount importance.

Remember, a storage combi boiler is a long-term investment for your home. It's vital to take all these factors into consideration to find the right boiler that suits your requirements, budget, and personal preferences.

Efficiency and Environmental Impact

Storage combi boilers boast several advantages regarding energy efficiency and environmental impact. Their Energy Efficiency Class A rating contributes to reducing energy bills for households while leaving a smaller carbon footprint.

The design of a storage combi boiler allows it to draw water from the mains and heat it up immediately, offering instant hot water. Additionally, it stores some water in the hot water cylinder, making it accessible for different parts of a household without affecting the flow rate. This dual function helps use fuel more effectively and efficiently.

Moreover, storage combi boilers are compact in size, making them suitable for small flats or houses with limited space. As a result, they require less material to produce, subsequently lowering their manufacturing carbon footprint and promoting more sustainable living.

To summarise, storage combi boilers offer several advantages when considering energy efficiency and environmental impact:

  • Energy Efficiency Class A rating

  • Reduced energy bills for homeowners

  • Smaller carbon footprint due to efficient fuel usage

  • Compact and space-saving design

  • Less material required for production, lowering manufacturing emissions

Professional Installation and Service with iHeat

When it comes to getting a storage combi boiler installed in your property, choosing a reputable company such as iHeat is essential. A storage combi boiler combines both a hot water and central heating system in one unit, making it an efficient choice for your home. However, proper installation and maintenance are crucial for its effectiveness, longevity, and safety.

iHeat is a reliable provider of boiler installations, offering professional heating engineer services to ensure your storage combi boiler is set up correctly. With the right experience and expertise, iHeat can seamlessly integrate both the heating and hot water aspects of your new boiler system, giving you peace of mind that your home will stay warm and comfortable.

In addition to installation, iHeat offers regular boiler service plans, which can play a vital role in keeping your storage combi boiler operating efficiently and safely over time. Regular maintenance and servicing performed by an expert heating engineer can reduce the likelihood of needing repairs and can potentially spare you hefty costs later down the line.

When you invest in a storage combi boiler with iHeat, you can benefit from their boiler plan, including guarantees and warranties. These offers provide the added security of knowing your investment is protected should any issues or complications arise. With the option to purchase an extended warranty, you can have confidence that iHeat will support you and your boiler system for years to come.

Using iHeat's professional installation and service, you can expect high-quality workmanship, commitment to industry standards, and dedicated customer service, ensuring that your storage combi boiler meets your heating and hot water needs flawlessly. Your satisfaction and the efficiency of your new system are the top priorities when you choose iHeat as your boiler installation and maintenance provider.

Advantages and Disadvantages

A storage combi boiler is an innovative heating system that combines the features of a traditional combi boiler with the benefits of a hot water cylinder. It is designed to efficiently provide both central heating and hot water to your home. In this section, we'll explore the advantages and disadvantages of storage combi boilers.

One of the main advantages of a storage combi boiler is its ability to save space. Since it combines the functions of a water heater and a central heating system into a single unit, there is no need for a separate hot water cylinder or cold water tank. This makes it an ideal choice for homes with limited space or for homeowners who wish to free up room for other purposes.

Another advantage is the reduced amount of pipework required, as storage combi boilers do not need separate connections for hot water and central heating. This makes for a cleaner and more streamlined installation process. In addition to being easier to install, the reduced pipework also means that there are fewer potential points of failure, which could lead to leaks or other issues down the line.

However, there are also some disadvantages associated with storage combi boilers. One potential drawback is that their capacity to store hot water can sometimes be limited compared to traditional systems with dedicated hot water cylinders. This may result in periods of reduced hot water availability, particularly during times of high demand, such as early mornings or evenings.

Another disadvantage is that storage combi boilers may be less energy-efficient than other types of boilers. Although they generally have high-efficiency ratings, the inclusion of storage tanks can sometimes lead to increased heat loss compared to combi boilers without built-in storage. This may result in slightly higher energy bills for homeowners.

In summary, storage combi boilers have a number of advantages, including space-saving design, easy installation, and reduced pipework. Nonetheless, potential disadvantages such as limited hot water storage capacity and potentially lower energy efficiency should also be considered when choosing the right heating system for your home.

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Frequently Asked Questions

Are storage combi boilers worth it?

Storage combi boilers can be a great option for households with higher hot water demand. They work by combining the benefits of a combi boiler with an internal hot water cylinder, ensuring a constant supply of hot water. For smaller properties or those with lower hot water needs, a standard combi boiler might suffice. Ultimately, weighing the benefits against the costs will help determine if a storage combi boiler is worth it for your household.

Can you have a storage tank with a combi boiler?

Typically, combi boilers provide hot water on demand from the mains supply and do not require a separate storage tank. However, storage combi boilers do feature an internal hot water cylinder, which allows them to support higher hot water demands without affecting the water flow rate. Consequently, it's possible, only with storage combi boilers, to have a storage tank within the boiler unit itself.

Can I use an unvented cylinder with a combi boiler?

An unvented cylinder is not necessary with a combi boiler system, as they heat water directly from the mains and supply it on demand. Unvented cylinders are more commonly used with system boilers, where a separate hot water cylinder stores the heated water.

Can you have an airing cupboard with a combi boiler?

In traditional systems with hot water cylinders, an airing cupboard is often used to store towels and linen. Since combi boilers don't utilise a separate hot water cylinder, there is no need for an airing cupboard. However, storage combi boilers do have an internal hot water cylinder, allowing you to have an airing cupboard if needed.

Does a combi boiler in a cupboard need ventilation?

Yes, ventilation is crucial for any boiler housed in a cupboard or confined space. Regardless of the boiler type, proper ventilation ensures the appliance operates safely, preventing the build-up of potentially dangerous gases. Always refer to the manufacturer's guidelines for your specific boiler model to determine the required ventilation standards.

Are storage combi boilers energy efficient?

Storage combi boilers are generally energy-efficient, combining hot water and central heating systems in one unit without the need for a separate water storage tank. The high efficiency is due to their ability to provide hot water on demand, reducing energy wastage associated with stored hot water cooling down and reheating. Moreover, modern storage combi boilers often come with energy-saving features and accreditations, further improving their efficiency.

Can you use a boiler cupboard for storage?

While it's possible to use a boiler cupboard for storage, cautious measures should be implemented. Ensure that you follow the manufacturer's guidelines regarding the minimum clearance space required around the boiler. Additionally, avoid storing flammable materials or chemicals near the boiler. It's best to consult an expert if you're unsure about using your boiler cupboard for storage purposes.

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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.