condensing combi boiler

Combi Boiler with Tank

What is a Storage Combi Boiler?

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

Whilst a standard combi boiler draws cold water directly from the mains supply and heats this water on demand, a storage combi not only does this but also stores a supply of hot water too in its very efficient thermal store. 

Storage combi boilers produce and deliver pressurised hot water similar to a system boiler with a hot water cylinder. The key difference being that the cylinder itself is housed inside the boiler unit itself. By storing the heated water this way whenever it’s needed, these boilers come with some great space-saving benefits and are able to deliver hot water to several taps, baths and showers at the same time without the flow rate being affected. These boilers can deliver up to 25l/min flow rate, however, this is dependent on your incoming cold water flow rate.

Previously many boiler manufacturers offered larger floor standing storage combi boilers. Due to the size of these, the scope for where they could be installed was very limited. To make this type of boiler more accessible to customers with different property sizes, many boiler manufacturers have now introduced compact storage combi boilers that can be wall-mounted and installed in properties of all sizes.

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The Components of a Storage Combi Boiler

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

Storage Combi Boiler Components

  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 and make use of innovative technologies, there are storage combi boilers that can provide hot water levels equivalent to a 150L unvented cylinder without needing the space to house a 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 in the above point, 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 boiler with a hot water tank should be a consideration

You have a large family

If you have a large or growing family, a storage combi boiler will be perfect. With multiple family members in one household, you will inevitably find that everyone will want hot water at the same time. 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, simultaneously through multiple outlets

They are easy to install

Storage combi boilers are easy to set up and install for the engineer, this means the installation time is reduced for you and you will have heating and hot water sooner

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What Properties are Storage Combi Boilers Suitable for?

Smaller sized combi boilers with tanks are well suited to larger apartments or flats where there is no space for an open vent or system boiler but there is a high hot water demand. Whilst storage combi models with a larger water storage capacity are suitable for larger family homes with more than one bathroom. 

Ultimately, regardless of whether you live in a flat or an apartment, semi-detached or detached home, 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 suitable for your property.

Advantages of a Storage Combi Boiler

  • 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 of a Storage Combi Boiler

  • More expensive than a standard combi boiler
  • Larger in size than standard combi boilers

What Size Storage Combi Boiler Do I Need?

When choosing a storage combi boiler, it’s important 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, which is why CLS (Cylinder Loading System) has become such a standard in the industry.

Storage combi boilers such as the Viessmann 222-F and 242-F offer the domestic hot water convenience of an unvented cylinder with twice the capacity (200 to 300 litres).

What is CLS (Cylinder Loading System) Technology?

It gets mentioned a lot when talking about storage combi boilers, but what does it actually mean?  Most unvented cylinders use a heating coil to heat up the cylinder. CLS technology specifically replaces this coil with a plate heat exchanger.  A DHW (Domestic Hot Water) pump circulates the cold water from the bottom of the cylinder, through the plate heat exchanger and puts the hot water back to the top of the cylinder.

The Best Storage Combi Boilers

Our recommendations

1. Viessmann 111-W Storage Combination Boiler

Viessmann Vitodens 111-W

This 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 and can fill a standard bath in 8 minutes, while simultaneously also supplying a sink or washbasin.  

All Viessmann boilers modulate energy usage between 5kw and 30kw when not in use, so energy efficiency is always high on their agenda, saving you money on your energy bills.  The advanced sensor technology allows constant output temperatures to be maintained even under high demand.  

This storage combi boiler can also be controlled with a tado° thermostat and smartphone app.  

Viessmann 111-W Storage Combi Boiler Key Features

  • Dimensions (H x W x D): 900mm x 600mm x 480mm
  • 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 separate 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

Find out more in our Viessmann 111-W Storage Combi Boiler Review

2. Vaillant ecoTEC plus Combination Store

Vaillant ecoTEC plus Combination Store

This 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 is a much thicker boiler compared to the wider Viessmann.  Due to the range of choice customers now have to suit their individual homes, it’s important to take proper measurements and consult a heating expert so that you’re buying a boiler that’s suitable for your property.

3. Glow-worm Energy 35 Store Combi Boiler

Glow-worm Energy 35 Store Combi Boiler

The Energy 35 Store is a fully integrated wall-mounted combi boiler with a tank, providing efficient heating ideal for larger properties. The two 21 litre insulated tanks housed inside the unit provide a short reheat time of fewer than 5 minutes.  As a brand owned by Vaillant, the  Energy 35 Store offers another solution in the world of combi boilers that includes a storage tank.

Glow-worm Energy 35 Store Combi Boiler Key Features

  • Two highly-insulated 21-litre integrated tanks provide high-performance heating and instant hot water supply to larger properties
  • Fast re-generation times of less than 5 minutes for hot water demands and quicker than hot water cylinders
  • Avoids the need for a hot water cylinder to free up space and reduces complexity and cost of installation
  • Lower running costs as the unit’s modulating Grundfos pump adapts to actual heating and hot water demand
  • 7-year guarantee with the option to extend

Our Recommended Storage Combi Boilers for Larger Homes

Viessmann Vitodens 222-F Storage Combi Boiler

Viessmann Vitodens-222-F

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

The Vitodens 222-F is designed to easily fit into a kitchen, 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
  • Integral loading cylinder
  • Inox-Radial stainless steel heat exchanger
  • Modulating Matrix cylinder burner
  • 100-litre cylinder with thermal insulation
  • Compatible with Viessmann’s ViStart and ViCare 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

Viessmann Vitodens 242-F Storage Combi Boiler

Viessmann Vitodens 242-F Storage Combi Boiler

The Viessmann Vitodens 242-F is a floor standing gas storage combi boiler that has been designed to make use of futureproof technology, specifically solar. To enable it to utilise solar energy, the Vitodens 242-F can be directly connected to Viessmann’s Vitosol solar collectors for water heating and central heating backup.

The Vitodens 242-F is equipped with an integrated 170-litre hot water storage tank.

Like the Viessmann Vitodens 222-F, the Vitodens 242-F features a compact width and depth, which make it ideal for installation into a kitchen.

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 permanently 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
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