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Last updated: 22nd April, 2024


Best Combi Boilers For Kitchen Cupboards

Best Combi Boilers For Kitchen Cupboards

Key takeaways

  • Combi boilers are dual purpose appliances providing both central heating and hot water for a property.
  • Combi boilers, especially the latest and greatest can easily fit into a kitchen cupboard.
  • Combi boilers are not only great at heating a property, but also reducing outgoings due to their efficiency.

A combi (combination) boiler is a type of domestic boiler that ‘combines’ a home’s central heating and hot water production into one succinct unit.

As an online boiler installation company, we understand the importance of having a reliable and efficient heating system in your home. 

Combi boilers are a popular choice for many homeowners, especially those who have limited space in their kitchen cupboards. 

In this blog, we will discuss the benefits of combi boilers and recommend specific models from popular brands that are ideal for kitchen cupboards.

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Combi Boilers Explained

Before we dive into the complexities of combis, if you aren’t completely sure what one is, don’t worry, allow us to explain.

A combi (combination) boiler is a type of domestic boiler that ‘combines’ a home’s central heating and hot water production into one succinct unit.

A combi takes water directly from the mains and heats it upon usage. After detecting a hot water request, the combi begins to burn gas in a combustion chamber. 

The hot gases rise and move through a series of pipes and into a component called a heat exchanger, the hot gas running through the exchanger then heats the surrounding cold water.

In a conventional boiler system, this process is done according to a programme and the water is stored in a separate cylinder until it’s needed. 

A combi only starts this cycle upon request (initiating the heating or turning on a hot water outlet), therefore the hot water is almost instant.

Combi Boiler Advantages

As mentioned, modern combis are an extremely popular type of boiler, this is down to their myriad of benefits, including:


Most modern combi boilers are extremely efficient in their heating of a property, with ErP ratings of ‘A’ and 90% conversion efficiencies, meaning hardly any energy used to produce heat is wasted.

Age of Boiler

Efficiency Percentage

Efficiency Rating (ErP)

0+ Years

90% +


10+ Years

85% +


15+ Years

80% +


20+ Years

70% +


25+ Years

60% +


The direct correlation between a boiler's age and its efficiency is clear to see in the newer systems’ ErP. 


Due to the compact casing and combined dual functionality of a combi boiler, essentially they perform the job of two appliances (conventional boiler and water storage tank), while occupying minimal storage space.

Most combis are small enough in dimension to fit easily into a standard kitchen cupboard, meaning they never detract from the decor or purpose of an internal space.

Water Pressure & Speed

Combi boilers take their water supply directly from the mains, this means the water circulating through the home’s central heating system retains a lot of the substantial flow pressure

A conventional boiler often relies on gravity to collect water, whereas a combi’s flow is much stronger and reduces the likelihood of water becoming stuck or ‘pooling’ in curved pipes due to the extra force behind the flow.

A combi boiler can produce instantaneous hot water, which is obviously beneficial for any property. 

Any Home with multiple bathrooms and an old, inefficient heating system may have to accommodate slower water heating speeds, increasing energy wastage, and as a result, energy bills.


Due to their modernity and consumer convenience based design, many combis can be synced with and remotely controlled by technology, such as smart thermostats or apps via a smartphone or tablet. 

This convenience in being able to wirelessly control your property’s temperature is game changing for homeowners, with some apps even being able to detect component faults and automatically notify an engineer.

Water Quality

Water produced from new combi boilers is clean and safe to drink, as it hasn’t been stored in a tank for any amount of time. This reduces the potential of sludge, rust or debris build up contaminating the water supply for a home.

Cheap To Run

Gas is among the most cost effective types of fuel for a heating system, coming in at almost three times cheaper than electricity as an operating fuel.

This indicates once the boiler unit and installation has been paid for, the boiler’s efficiency and low cost fuel will start to pay for itself in money saved much faster than you’d think!


Most modern combis have been designed with operational volume in mind, often excelling in minimising any sound output, with most top of the line boilers being silent when switched on.

Premium boiler brands often receive Quiet Mark awards for their success in acoustical consideration and volume reduction.


Many combi boilers can run on a variety of fuels, gas being the most popular, and can even operate on mains gas or LPG.


Due to their popularity, combi boilers and their replacement parts are very prevalent. This means even if your combi has a problem, their superior availability ensures that there is always an abundance of replacement components that are cheap and easy to source.

Combi Boiler Costs

As with any boiler type, the unit cost and installation rate for a new combi will be manufacturer and merchant dependent.

Average iHeat combi boiler Installation list (guide only):

Installation Type

Price (inc VAT)

Combi to combi swap


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System to combi conversion


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New boiler install


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Back boiler to a combi


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When Should You Replace A Boiler

As a general rule of thumb, any boiler 15 years or older should be replaced. In the time elapsed since the boilers installation the constant advancement in modern technology means upgrading to a newer boiler will work out more efficient, cheaper and safer.

Any boiler with signs of serious degradation, function failure or that has been ‘condemned’ by an expert heating engineer must be immediately disconnected and replaced for safety reasons as well as heating convenience.

Back Boiler To Combi Conversion

An old, inefficient back boiler can actually be converted to either a combi or system boiler, systems can work out cheaper in terms of the conversion due to a lot of the pipework remaining the same. 

However, most people opt for the combi conversion as an upgrading of the entire system could be more efficient in the long run, and may ensure less future faults, reducing repair or maintenance costs.

Secondly, you will need to decide upon the new flue placement of a combi for example, you could keep the same vertical flue position, releasing gases out of the chimney or move it due to the fact combis can operate with a vertical or horizontal flue.

Thanks to the compact design of modern combi boilers, they can be positioned into smaller spaces like a standard kitchen cupboard, or they can be placed in the same spot as the boiler being removed (if you want your boiler moved to a new location there will be additional fees, especially if there is no piping in this area).

The fire will need to be removed, followed by the old boiler, flue, tanks and all relevant piping will be re-routed or installed. Post new boiler installation any area repairs to surrounding walls or where the fire previously was will need carrying out and safety checking.

How Long Does A Combi Installation Take?

Each combi boiler install is a unique case and therefore any time indication is intended as a rough guide only.

For a combi to combi swap we advise to allow for up to 1 full day and for a conversion from a different type of boiler to a combi, we advise to allow for up to 2 full days.

Where Can Combi Boilers Be Installed?

A combi boiler is a versatile appliance that can be installed in several different locations around the property.

Combi boilers are extremely space economic and as mentioned above the most popular place for a combi is in a kitchen or utility cupboard.

Providing the property has suitable insulation amongst other things, a combi can also be stored in a loft or garage.

Other common housing places for a combi boiler include the utility room, bedroom or a basement.

Best compact Combis for Kitchen cupboards

There are many different models of combi boilers available from popular brands such as Worcester Bosch, Vaillant, and Ideal. Here are some specific models that we recommend for kitchen cupboards:

Worcester Bosch Greenstar CDi - Dimensions: W 390mm, D 280mm, H 680mm

The Worcester Bosch Greenstar CDi Compact is a bite size combi boiler that was specifically designed to fit within a standard kitchen cupboard. Despite its compact size, this combi boiler still delivers incredible heating and hot water, with a range of outputs available to suit different homes.

Winner of the Which? Best Buy Gas and Oil Boilers award in September 2021 and produced by one of the most reliable boiler manufacturers on the market, you can count on this boiler to deliver effective and efficient heating for a long time, keeping your home warm with much lower running costs.

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Vaillant ecoTEC Plus 825 - Dimensions: W 440mm, D 338mm, H 720mm

Extremely compact, versatile and powerful, the not to be underestimated ecoTEC plus  in its 25kW size can be a dream edition to your kitchen.

Well crafted and with the dimensions to be extremely space economic, the ecoTEC plus 825 is highly efficient and comes with built in frost protection, as well as quite mark accreditation for its sonic reduction capabilities.

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Viessmann Vitodens 100-W - Dimensions: W 400mm, D 350mm, H 700mm

Efficient, compact, quiet and affordable, the Viessmann Vitodens 100-W combi boiler is the most popular solution available at iHeat. Reviewed as a Which? Best Buy in 2019, the Vitodens 100-W features innovative technology and services combined with reliability and longevity.

This combi helps you to optimise your heating and save on energy costs and can all be done from inside your kitchen cupboard.

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Ideal Logic+ Combi - Dimensions: W 395mm, D 279mm, H 700mm

The Ideal Logic Plus Combi boiler is a fantastic little appliance, scoring highly on efficiency and delivering speedy heating and hot water, all whilst being able to tuck away neatly into a kitchen cupboard.

The boiler is supported by the Queen’s Award for Enterprise 2013 and the Good Housekeeping Reader Recommended Status in 2013 and 2017, so you can be sure it’s a good choice!

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Combi boilers are a great choice for homeowners who want a reliable and efficient heating system that does not take up too much space. They are easy to install, convenient, and can lead to significant energy savings.

Frequently Asked Questions

Can a combi boiler be fitted in a kitchen cupboard?

Yes, a combi boiler can be fitted in a kitchen cupboard, provided there is enough space for installation and maintenance access. The cupboard must also meet the boiler manufacturer's clearance requirements for safe operation.

Does a combi boiler in a cupboard need ventilation?

Yes, a combi boiler installed in a cupboard requires adequate ventilation to ensure safe and efficient operation. The specific ventilation requirements will depend on the boiler model and manufacturer guidelines.

Can you put a Worcester Bosch boiler in a cupboard?

Yes, a Worcester Bosch boiler can be installed in a cupboard. Worcester Bosch offers compact models designed for such installations. However, it's important to ensure that the installation complies with the manufacturer's space and ventilation requirements.

What is the most reliable combi boiler?

The most reliable combi boiler brand often varies depending on consumer reviews and professional surveys. Brands like Worcester Bosch, Viessmann, and Vaillant frequently rank high in reliability and customer satisfaction.

What boilers do plumbers recommend?

Plumbers often recommend reputable brands known for their reliability, efficiency, and customer support, such as Worcester Bosch, Vaillant, and Viessmann. The specific recommendation may vary based on the plumber's experience and the specific needs of the homeowner.

What is the number 1 boiler in the UK?

The "number 1" boiler can vary based on different criteria, such as sales, reliability, or customer satisfaction. However, Worcester Bosch is often cited as a leading brand in the UK for its comprehensive range of high-quality, reliable boilers.

What are the top 3 boiler brands?

The top three boiler brands in the UK, based on reliability, customer satisfaction, and expert recommendations, are typically Worcester Bosch, Vaillant, and Viessmann. These brands are known for offering efficient, durable, and technologically advanced heating solutions.

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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.