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1,567 reviews

Storage Combi Boilers Explained

Becky Mckay
By: Becky Mckay
Updated: 17th June 2022

Storage combi boiler

Does your home have high hot water demand but little space? Then a storage combi boiler could be for you.

Storage combi boilers have many benefits of combi boilers with the addition of an internal hot water cylinder. This allows them to meet higher demand for hot water than the more familiar combi boiler.

What is a storage combi boiler?

A storage combi boiler works like a combi boiler but stores hot water in a cylinder. So hot water isn’t sent directly to the hot water tap as and when you need it like how a combi boiler works.

Storage combi boilers combine the benefits of combi and system boilers. This gives homeowners with no space for a separate hot water cylinder, a solution that can meet high demand for hot water. As water can be sent to several taps, baths or showers at once without the pressure dropping (as it would with a combi).

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How are they different from combi and system boilers?

A combi boiler is a storage combi boiler without the internal cylinder. While a system boiler does store hot water in a cylinder but it’s separate to the boiler.

Combi boilers are the perfect choice for smaller homes that don't have high demand for hot water. But, they're not able to provide a strong flow of hot water to more than 1 hot tap or shower at a time. Typically, a system boiler would be recommended as an alternative, because they store hot water in a cylinder. Not all homes have space to spare for a boiler as well as a cylinder though and that's where a storage combi boiler can help.

Storage combi boiler advantages

If you're in a position where you're considering whether to have a combi or system boiler installed, you might want to consider the advantages of a storage combi boiler.

Hot water cylinder within the unit

The main benefit of storage combi boilers is that you don't need to have the space in your home for a boiler and a separate hot water cylinder. Instead, the cylinder is within the boiler.

Meet high demands for heating and hot water

Combi boilers heat water from the mains as and when heating or hot water is needed, which is ideal for getting instant hot water but not so great for properties with a higher demand for heating and hot water.

By storing hot water, that can be set to multiple outlets at once, storage combi boilers are able to meet higher heating and hot water demands.

Cheaper than a system boiler

As everything is housed within the unit itself, there's no need for an external hot water cylinder or tank, like there is with a system boiler. This makes storage combi boilers not only cheaper in terms of the unit but when it comes to the installation too.

Solar thermal compatible

By storing hot water, storage combi boilers give you the option to keep that water warm with solar thermal, something that isn't possible with a conventional combi boiler.

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Best storage combi boilers

There are very few storage combi boilers on the market. Especially when compared to combi, system and regular boilers.

Fortunately, the storage combi boilers that are available have been manufactured by a number of leading boiler brands. Including, Glow-worm, Vaillant and Viessmann.

How much hot water the boiler can store is an important comparison to make when looking at the best storage combi boilers. The biggest capacity (by quite a long way) is the Viessmann 222-F range which can store 100 litres of hot water.

Storage combi Storage capacity
Glow-worm Energy Store 35 2x 21 litre tanks
Vaillant ecoTEC Plus 938 15 litres
Viessmann 111-W 26 46 litres
Viessmann 111-W 35 46 litres
Viessmann 222-F 100 litres

As well as capacity, you also need to look at output, flow rate and efficiency.

Boiler Model Efficiency CH output DHW output Flow rate
Vaillant ecoTEC Plus 938 94% 30.9 kW 38.7 kW 20 l/min
Glow-worm Energy 35 89.4% 31 kW 35.7 kW 19.7 l/min
Viessmann 111-W 26 94% 25 kW 30.3 kW 20.1 l/min
Viessmann 111-W 35 94% 32 kW 33.9 kW 21.2 l/min
Viessmann 222-F 19 94% 19 kW 21.8 kW 18.2 l/min
Viessmann 222-F 25 94% 25 kW 28.3 kW 23 l/min
Viessmann 222-F 35 94% 32 kW 33.5 kW 11.4 l/min

Vaillant ecoTEC Plus 938

The Vaillant ecoTEC Plus 938 is able to deliver hot water to an outlet within 5 seconds of it being turned on and provides 20 litres per minute. Hot water is stored in a 15 litre actoSTOR cylinder, which aids performance and can be refilled in only a couple of minutes.

Storage combi boilers typically take up more space than conventional combi boilers but Vaillant have reduced the width of the ecoTEC Plus 938 by making it thicker. With dimensions of 720mm x 440mm x 600mm (HxWxD), this is one of the smaller storage combi boilers on the market.

Glow-worm Energy 35

Glow-worm have gone one further with their storage combi boiler by having not 1 but 2 insulated tanks within the unit, doubling the storage capacity from 21 to 42 litres.Once the tanks are empty, there's only a short 5 minute time frame until they're both full of hot water again.

Like the Vaillant ecoTEC Plus 938, this Glow-worm boiler is also, thicker rather than wider, with dimensions of 890 x 470 x 561 (HxWxD), possibly down to the fact that they're owned by Vaillant. Plus, as a wall-mounted unit, you'll be saving space around the home.

Viessmann 111-W

The 46 litre hot water storage tank housed within the Viessmann 111-W is the highest capacity of the 3 storage combi boilers we've looked into here and is ideal for large flats or homes with 2 bathrooms. This is a wide boiler, with dimensions of 900mm x 600mm x 480mm (HxWxD) so it will take up more space than the Vaillant storage combi boiler.

Viessmann 222-F

The Viessmann 222-F can meet very high demands for hot water. This is thanks to an internal storage cylinder with a capcity of 100 litres. To put that into context, some separate hot water cylinders store between 75 and 180 litres.

It’s fitted with a stainless steel heat exchanger for reliable and efficient performance. This helps it achieve efficiencies as high as 98% as it heats your home and hot water. Plus, it will do so with little noise.

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How much does a storage combi boiler cost?

Storage combi boilers are priced around £1,500 but this will vary from model to model. The table below includes prices the popular storage combi boilers we looked at above.

It's also important to make a note of the warranty period as during this period, you're protected by the manufacturer should there be an issue with the boiler.

Storage combi Typical price Max warranty
Vaillant ecoTEC Plus 938 £1,703 10 years
Glow-worm Energy 35 £1,580 7 years
Viessmann 111-W £1,600 – £2,000 7 years
Viessmann 222-F £2,600 – £3,000 5 years

Storage combi boiler disadvantages

As well as the advantages that storage combi boilers have over both combi boilers and system boilers, it's worth noting the possible downsides.

Larger than a combi boiler

Having a hot water cylinder within the unit means that a storage combi boiler is larger in size than a typical combi boiler. However, depending on the size of the hot water cylinder you need, many can be wall-mounted.

Cylinder size determines hot water access

Depending on the model of storage combi boiler, the size of the hot water cylinder will be different. This means that different storage combi boilers are able to store varying levels of hot water. It's important to note the size of the cylinder and how long it takes to refill (which can be as little as 5 minutes).

Tend to be more expensive than a combi

As a combi boiler with the additional benefit of having a hot water cylinder within the unit, they can naturally end up costing more than a conventional combi boiler.

Should you install a storage combi boiler?

Storage combi boilers are the best choice for homes with 1-2 bathrooms and a demand for heating and hot water that's too much for a combi boiler. When considering a replacement boiler and a combi boiler isn't powerful enough, then it would be normal to then look into having a system boiler installed, however, this is only possible if you have the space available for a hot water cylinder.

Rather than committing more space around your home to a new heating system by installing a system boiler, a storage combi boiler could well be the answer.

Combi and system boilers are typically available at a lower price than storage combi boilers, starting at around £500, but higher-end models will be of a similar price to storage combi boilers. It's worth noting that when it comes to installation, a system boiler is likely to cost more as an external hot water tank will need to be installed.

Get free storage combi boiler quotes

Once you've found the most suitable boiler type for your home, whether it's a storage combi, combi or system, then comparing multiple installation quotes will give you the greatest chance of getting the best possible deal.

To help you in finding multiple quotes, use our simple online form, letting us know the details about the work, and you'll be contacted by up to 3 local installers. Each will provide a free no-obligation quote, for you to then compare once you've received them all.

Becky Mckay

About the author

Becky Mckay

Becky is one of our home heating and renewable energy experts and has a wealth of experience writing about the world of heating.

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