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Storage Combi Boilers

Learn about storage combi boilers, what they are, who they are for, the internal parts and which one Boilerhut recommends.

A storage combi boiler is a combi boiler with a hot water tank. This allows them to provide hot water more quickly and can help reduce problems with water pressure. The hot water tank generally makes the units larger than ordinary combi boilers.

Here at Boilerhut, we regularly install storage combi boilers in homes across the UK. They’re a great product that fits between combi boilers and system boilers and their hot water tanks.

We can install storage combi boilers nationwide, and as we’re a Viessmann Premium Partner, Viessmann combi boilers and storage combi boilers are our speciality. We can offer excellent warranties and servicing through Viessmann themselves.

What does this guide cover?

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More Information About Combi Boilers

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Further Reading…

What does this guide cover?

More Information About Combi Boilers

< Back to the main combi boiler installation and details page

Further Reading…

What is a Storage Combi Boiler?

In simple terms, a storage combi boiler is a combi boiler with an integrated internal hot water tank (thermal water store). This means that it has a hot water cylinder housed within the boiler unit itself.

Storage Combi = Combi with hot water storage tank.

  • A standard combi boiler draws cold water directly from the mains supply and heats this water on demand (when you turn on a tap or shower).
  • A storage combi also draws cold water from the mains supply to heat on demand, but it also has a 46-litre supply in a tank. This allows it to add more water to the incoming mains during times of high load; when one person is in a shower and another turns on the hot tap, for example.

Storage combi boilers deliver pressurised hot water like a system boiler with a hot water cylinder. The critical difference is that the cylinder is housed inside the boiler unit, so everything is in one place.

These boilers have tremendous space-saving benefits by storing the heated water this way. They can deliver hot water to several taps, baths and showers simultaneously without the flow rate being affected.

These boilers can deliver up to 25l/min flow rate; however, this depends on your incoming cold water flow rate.

In the past, many boiler manufacturers only offered large floor-standing storage combi boilers. Due to the size of these, the scope for where they could be installed was minimal.

To make this type of boiler more accessible to customers with different property sizes, Viessmann and Vaillant have now introduced compact storage combi boilers that can be wall-mounted and can be installed in properties of all sizes.

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How Does A Storage Combi Boiler Work?

Combi boilers work by heating cold water from the mains supply through a heat exchanger and allowing it to flow through your home to a tap or shower.

Storage combi boilers do the same thing. But they can produce more hot water than the cold water mains or a standard combi boiler of similar power can supply when required due to their internal tank. It uses a cylinder loading system (CLS) to keep the water hot.

What is CLS (Cylinder Loading System) Technology?

Storage combi boilers use a cylinder loading system (CLS) to keep water hot. It takes cooler water from the bottom of the hot water tank and pumps it through the plate heat exchanger to keep the water hot. A traditional stand-alone hot water cylinder will use a heating coil to heat the water. The CLS is the internal, and more efficient storage combi process.

Read more about heat exchangers here >

The Components of a Storage Combi Boiler

Storage combi boiler - Vitodens 111-W breakdown

Storage combi boiler – Vitodens 111-W breakdown

Using the Viessmann Vitodens 111-W as an example, the diagram shows the components of a storage combi boiler:

  1. 46-litre stainless loading cylinder
  2. Stainless steel Inox-Radial heat exchanger
  3. Variable speed combustion fan
  4. Integral expansion vessel
  5. High-efficiency pump

Why Choose a Storage Combi Boiler?

You don’t have the space for a hot water cylinder

With an integrated hot water tank storage combi boilers can provide hot water levels equivalent to a 150L cylinder without needing the space to house an actual separate cylinder. This means you can save space in your garage, airing cupboard or loft and still get the hot water you need.

A system boiler isn’t suitable

Due to the space issues described above, this type of boiler is an ideal substitute for households where a system boiler cannot be installed.

You have a property with multiple bathrooms

If your property has more than one bathroom, this type of combi boiler with an internal hot water tank is a great option between a combi and a full system setup. Not sure if they’re right for you? Get an instant and free online quote with Boilerhut, and we’ll call you back to discuss your options.

You have a large family

A storage combi boiler will be perfect if you have a large or growing family. With multiple family members in one household, you will inevitably find that multiple people want hot water simultaneously. Whether the hot water demands are from the shower, the bath, or the kitchen sink, a storage combi boiler is equipped to deliver hot water as and when you need it through multiple outlets.

They are easy to install

Storage combi boilers are easier to set up and install for a heating engineer than a full system but more complicated than a traditional condensing combi boiler. This helps reduce installation time, getting you heating and hot water as soon as possible.

Viessmann combi boilers

We specialise with Viessmann because we believe they provide a premium product with superior parts, warranty and servicing options. Viessmann combi boilers offer industry-leading efficiency and can save you money on your gas bills paying back their initial installation cost in just a few years.

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What Properties Are Storage Combi Boilers Suitable For?

Storage combi boilers are excellent for mid-sized homes and large flats or apartments. If a traditional combi boiler can’t provide the hot water needed for your property, a storage combi boiler is a great option if an entire system boiler is overkill.

If you have two bathrooms that might use hot water simultaneously, storage combi boilers could be a great option. You get to keep your cupboard space, and a model like the Viessmann Vitodens 111-W can be put on the wall like a standard combi boiler.

Ultimately, regardless of whether you live in a large flat or an apartment, semi-detached, detached or terraced home, if your household has high hot water demands and housing a separate hot water cylinder isn’t suitable, there will be a storage combi boiler ideal for your property.

Advantages And Disadvantages Of A Storage Combi Boiler

Advantages

  • Cheaper to purchase and install than open vent and system boilers.
  • Great for saving space: no need for attic tanks or hot water cylinders.
  • Easy to install and set up for the installer.
  • Compact size; some models can fit inside a kitchen cabinet.
  • Options available for properties of all sizes.
  • They provide the ability to deliver hot water to multiple sources simultaneously.
  • They offer the same money-saving benefits of a standard combi boiler by only providing hot water when it’s needed.

Disadvantages

  • More expensive than a standard combi boiler.
  • Larger than standard combi boilers.
  • More complicated internal mechanisms.
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What Size Storage Combi Boiler Do I Need?

When choosing a storage combi boiler, it’s essential to consider the size of the property in relation to how much water will need to be heated throughout. Don’t be afraid to take advantage of the space if you have it. Space-saving is one of the most important benefits of a storage combi boiler.

When thinking about size, there are two things to consider: how much water you’ll need, and how much room you have.

The Viessmann Vitodens 222-F 32kW is a large, floor-standing storage combi boiler with a 100-litre hot water tank that offers the equivalent hot water of a 300-litre system boiler cylinder.

The Viessmann Vitodens 111-W is a wall-mounted boiler and larger than combi boilers of similar power. It’s available in 25kW and 32kW versions. The 111-W has a 46-litre hot water tank, which provides water equivalent to a stand-alone 150-litre hot water tank.

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The Best Storage Combi Boilers

Our recommendations:

1. Viessmann 111-W Storage Combination Boiler

Viessmann Vitodens 111-WThis is a high-performance storage combi boiler, perfect for a larger flat or a family home with high demand for hot water on a daily basis.  With its CLS technology (Cylinder Loading System) and 46-litre integrated stainless steel storage tank, this storage combi boiler produces 18 litres of hot water per minute. It can fill a standard bath in 8 minutes while supplying a sink or washbasin.

All Viessmann boilers modulate energy usage, so energy efficiency is always high on their agenda, saving you money on your energy bills.  The advanced sensor technology maintains constant output temperatures even under high demand. Modulation allows a boiler to reduce heating power from its maximum output; a Vitodens 111-W can modulate from 2.9kW to 32kW.

This storage combi boiler can also be controlled with a tado° thermostat or the new Viessmann smart thermostat and smartphone app.

Please read our full review >

Key Features:

  • Dimensions (H x W x D): 950mm x 600mm x 500mm
  • Cylinder loading system (CLS) and integrated stainless steel storage tank
  • User-friendly control via backlit LCD touchscreen
  • High hot water capability with a flow rate of 18 l/min
  • Available in outputs from 4.7 to 35.0 kW
  • Hot water performance equivalent to a separately installed 150L cylinder
  • User-friendly dials for rapid adjustment of heating and hot water
  • Energy efficiency class: A
  • Optional wireless remote control available
  • Optional solar thermal backup
  • Up to 10 years extended warranty available with Boilerhut

2. Vaillant ecoTEC plus Combination Store

Vaillant ecoTEC pro storage combiThis combi boiler with a hot tank from Vaillant delivers great performance with lower energy consumption.  It produces 20 litres per minute of hot water when needed, and then modulates to using only 16% power, saving you fuel and money.

Vaillant ecoTEC plus Combination Store Key Features

  • ErP A rated for both hot water and heating efficiency
  • Dimensions (H x W x D): 720mm x 440mm x 600mm
  • Integrated hot water storage device at the back of the boiler
  • Hot water within 5 seconds
  • Flow rate of up to 20 l/min
  • A wide range of heating control options are available
  • 5-year guarantee as standard, with 7 to 10 years available when you book a Vaillant Advance installer

The Vaillant isn’t as tall or wide as the Viessmann 111-W, but it is much deeper. It’s essential to take proper measurements and consult Boilerhut engineers when buying a boiler to ensure it will fit where you want it installed. This boiler may not fit in most cupboards.

Feel free to read our full ecoTec combi review >

3. Glow-worm Energy 35 Store Combi Boiler (discontinued)

glow-worm 35 storage combiThe Energy 35 Store was a fully integrated wall-mounted combi boiler with a tank, providing efficient heating that was ideal for larger properties. The two 21-litre insulated tanks inside the unit gave a short reheat time of fewer than 5 minutes.

As a brand owned by Vaillant, the  Energy 35 Store offered another solution in the world of storage combi boilers.

Glow-worm Energy 35 Store Combi Boiler Key Features

  • Two highly-insulated 21-litre integrated tanks provided high-performance heating and instant hot water supply
  • Fast re-generation times of less than 5 minutes for hot water demands and quicker than hot water cylinders
  • Avoided the need for a hot water cylinder, freeing up space and reduced the complexity and cost of installation
  • Lower running costs as the unit’s modulating pump adapts to actual heating and hot water demand
  • 7-year guarantee with the option to extend
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Storage Combi Boilers for Larger Homes

Our recommendations:

1. Viessmann Vitodens 222-F Storage Combi Boiler

The Viessmann Vitodens 222-F is a floor standing gas storage combi boiler, designed for providing heat and hot water to large homes thanks to its integrated 100-litre hot water tank.

The Vitodens 222-F is designed to easily fit into a kitchen or utility room, both in terms of its looks and in terms of its standard kitchen unit dimensions, which allow for easy integration

Viessmann Vitodens 222-F Key Features

  • Rated heating output: 1.8 to 35 kW
  • Internal 100-litre hot water cylinder
  • Inox-Radial stainless steel heat exchanger
  • Modulating Matrix cylinder burner
  • Compatible with Viessmann’s apps
  • Colour touch-screen with a graphic display of energy consumption
  • No LPG conversion kit needed
  • 10-year guarantee when installed by a Viessmann-trained installer like Boilerhut

Read our full Vitodens 222-F review >

Large floor standing storage combi boilers

2. Viessmann Vitodens 242-F Storage Combi Boiler (Discontinued)

The Viessmann Vitodens 242-F was a floor-standing gas storage combi boiler designed to use solar technology alongside gas. The Vitodens 242-F was equipped with an integrated 170-litre hot water storage tank.

Like the Viessmann Vitodens 222-F, the Vitodens 242-F featured a compact width and depth, which make it ideal for installation in a kitchen or utility room.

Viessmann Vitodens 242-F Key Features

  • Integral solar cylinder
  • 5-inch colour touchscreen
  • Inox-Radial stainless steel heat exchanger
  • MatriX cylinder burner with Lambda Pro Control combustion controller for permanent high efficiency and clean combustion
  • Floor area of 0.4 m², so can fit into any recess
  • Compatible with Viessmann’s Vitoconnect 100 WLAN adaptor for smart home control
  • 10-year guarantee when installed by a Viessmann-trained installer like Boilerhut

Storage Combi Boiler Range

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Viessmann Vitodens 111-W

  • Size: 25kW, 32kW
  • Efficiency: 94% / A-rated
  • Warranty: 10 Years
  • Stainless Steel Heat Exchanger
  • 46 Litre Hot Water Tank
  • Up to 21.2 Litres/Min Hot Water
Read Our In-Depth Review

Vaillant ecoTEC plus combi store

  • Size: 25kW, 32kW
  • Efficiency: 89% / A-rated
  • Warranty: 10 Years
  • Stainless Steel Heat Exchanger
  • Up to 15.9 Litres/Min Hot Water

Viessmann Vitodens 222-F

  • Size: 32kW
  • Efficiency: 94% / A-rated
  • Warranty: 10 Years
  • Stainless Steel Heat Exchanger
  • 100 Litre Hot Water Tank
  • Up to 23 Litres/Min Hot Water

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Frequently asked questions

Yes. They’re great for properties that have low cold water flow rates, multiple bathrooms or no space for a more traditional boiler and hot water cylinder/tank. They aren’t for everyone, of course, but they’re a great option for some properties.

They work exactly the same way as a ‘normal’ combi boiler but they include a hot water tank. This allows them to push more water through the home than comes in through the cold water flow rate, for a temporary amount of time.

  • Combi boiler – an on-demnd heating and hot water unit that uses fuel, usually natural gas, LPG or oil. No need for separate hot water cylinders in the property.
  • Storage combi boiler – a combi boiler with an in-built hot water tank/cylinder for better hot water flow during high demand.
  • System boiler – a system boiler heats water and stores it in a large hot water cylinder, normally situated in an airing cupboard. Great for large hot water demand in large homes.
  • Storage combi boiler – a combi boiler with an in-built hot water tank/cylinder for better hot water flow during high demand, but not as high as a system boiler. A single unit: no external hot water tank.

A storage combi boiler is a ‘normal’ combi boiler that includes a hot water tank. This allows it to provide hot water instantly, with low cold water flow or when the demand is high.

Storage combi boilers come in differen sizes depending on your property’s requirements. They can be, pretty much, the same size as a ‘normal’ combi boiler. They can also be as large as a big single-door fridge – but these come with 170 litre hot water tanks.

We would pretty much always recommend the Viessmann Vitodens 111-W. This is a wall-hung storage combi boiler with a 46 litre hot water tank. It modulates 1:10 (meaning the 32kW version can run as low as 3.2kW saving you money) and is industry-leading rated as 98%/Class A efficient. Lastly, we can provide a 12 year warranty.

  • Size – They are generally larger than normal combi boilers so some people may struggle to put them in the same place as a previous unit.
  • Cost – They are generally more expensive due to the increase components and complexity.

Storage combi boilers have a hot water tank inside the unit. The size of the tank, and boiler, will depend on the amount of water the unit can hold. Our most popular storage combi is the Viessmann Vitodens 111-W, this has a 46 litre hot water tank.

Storage combi boiler prices are generally higher than a standard combi. This is because of the additional components, complexity and size of the unit. Alongside the storage combi boiler itself being more expensive, installation is more difficult because of the size. It can sometimes require two engineers to lift the unit into place which increases the labour cost.

Storage combi boilers are larger than normal combi boilers. As such, they are much heavier and will probably require two engineers to install them into a property. Get a quote online today and we’ll call you back to discuss your options.

Yes, you could, but it’s better to consider a storage combi boiler. They are relatively popular and Boilerhut installs a lot every year. They are larger and more expensive than standard combi boilers but provide more hot water flow.

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Witten by Bernard Morgan (Engineer).
First Published: December 4, 2023. Updated: December 8, 2023

More Information About Combi Boilers

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Further Reading…

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