Best Small Combi Boilers in 2025

Compact boilers are favoured by 70% of UK homeowners, and it’s not hard to see why. 

These small but powerful units are effective, efficient, and take up minimal space in your home. In fact, many leading manufacturers design new boilers to fit inside kitchen cabinets.

But don’t let their smaller size mislead you – these compact boilers are just as powerful as their larger counterparts, delivering excellent heating and hot water performance. 

So, if you’re looking for the right compact boiler for your home, we’ve done the legwork and found the top four performers from three reliable boiler brands.

Best Compact Combi Boilers For Kitchen Cupboards

• Best Value: Viessmann Vitodens 050-w
• Best Premium: Worcester Bosch Greenstar CDI Compact
• Best Price: Ideal Logic Plus
• Best for Saving on Your Energy Bill: Worcester Bosch Greenstar 4000

Model	Dimensions in mm (H x W x D)	Available Outputs
Viessmann Vitodens 050-w	700 x 400 x 300	3.2 to 19kW, 25kW, and 35kW
Worcester Bosch Greenstar CDI Compact	690 x 390 x 280	28kW, 32kW, 36kW
Ideal Logic Plus	700 x 395 x 278	24kW, 30kW, 35kW
Worcester Bosch Greenstar 4000	724 x 400 x 310	25kW, 30kW

If you are strongly considering putting your boiler in a kitchen cupboard, take a look at our guide that covers the best way to do it and the rules and regulations around it.

Best Value Compact Combi Boiler: Viessmann Vitodens 050-w

This is one of the most popular boilers in the Viessmann range and, in our opinion, one of the best combi boilers to buy right now.

Vitodens 050-w 25kw combi-boiler is ideal for small homes and flats

At 700mm in height, 400mm in width, and 300mm in depth, the Vitodens 050-w combi boiler is compact and perfectly fits in kitchen cabinets.

Ideal for homes with 3 bedrooms or more, this energy-efficient boiler has a lower hot water consumption than average, so it helps reduce your utility bills. 

The boiler can be set to modulate its output so it doesn’t always run at maximum power. This smart functionality helps to further minimise energy usage.

Vitodens 050-w30kw combi boiler is ideal for medium-sized homes

Vitodens 30kw combi-boiler is a great choice if you have two bathrooms. Thanks to its extra 5kw power, it can handle higher hot water demands.

This model can also be programmed to reduce its power so that it uses only as much energy as necessary to heat your home.

Vitodens 050-w combi-boiler: Efficiency

• A-rated for both heating and hot water
• Up to 97% efficiency rating
• Features a modulating burner
• Adjusts output to match your home’s heating needs
• Reduces energy consumption and costs

Vitodens 050-w combi-boiler: Prices

• Vitodens 050-W 25kW – £1,035
• Vitodens 050-W 30kW – £1,109
• Vitodens 050-W 35kW – £1,265

Vitodens 050-w combi-boiler: Warranty

• Standard 7-year warranty
• Up to 10-year extended warranty

Best Premium Compact Boiler: Worcester Bosch Greenstar CDI Compact

The Greenstar CDI Compact is a popular option for installers and property owners because of its cutting-edge features like EasyControl app compatibility, better ErP efficiency rating, and solar compatibility.

Its modest size is also a major plus, especially for UK homes with limited space where it can be fitted into a kitchen cabinet.

This Worcester Bosch offers great value and is one of the most compact combi boilers available. It has received five stars for efficiency and is generally regarded as an entry-level boiler as it’s simple to use, install, and operate.

Greenstar CDI Compact 28kW combi-boiler is ideal for small homes and flats

The 28kW model is perfect for smaller properties. It efficiently handles heating and hot water needs for 1-2 bedroom homes or flats.

Greenstar CDI Compact 32kW combi-boiler is ideal for medium-sized homes

For medium-sized homes, the 32kW version steps up to meet higher demands. This model balances power and efficiency, making it well-suited for 3-4 bedroom houses or properties with multiple bathrooms. 

Greenstar CDI Compact 36kW combi-boiler is ideal for large homes

The 36kW model is designed for larger homes with high heating and hot water demands. It’s perfect for properties with 4+ bedrooms or multiple bathrooms, ensuring consistent performance even during peak usage times without compromising on energy efficiency.

Greenstar CDI Compact combi-boiler: Efficiency 

• A-rated for both heating and hot water efficiency
• Up to 94% energy efficiency
• Features Greenstar Intelligent Filling System for optimal pressure maintenance
• Modulating burner adjusts output to match your home’s heating demands
• Low energy pump reduces electrical usage
• Standby mode minimises energy consumption when not in use

Greenstar CDI Compact combi-boiler: Prices

• Worcester Bosch Greenstar 28CDi Compact 24kW – £942
• Worcester Bosch Greenstar 32CDi Compact 32kW – £1,111
• Worcester Bosch Greenstar 36CDi Compact 36kW – £1,370

Greenstar CDI Compact combi-boiler: Warranty

• Standard 5-year warranty
• Up to 10-year extended warranty

Best Price Compact Boiler: Ideal Logic Plus

This British-made Ideal Logic model is a great choice for its high efficiency and user-friendly design featuring a clear digital display. It complies with all ErP requirements and operates on an A-rating performance standard.

If you’re looking for an inexpensive central heating system, we consider it an excellent entry-level option.

In addition, Ideal Heating is known for its excellent consumer-friendly after-sales care, so you can have peace of mind knowing that support is readily available if you ever need assistance with your boiler.

Ideal Logic Plus 24kw combi-boiler is ideal for small homes and flats

The 24kW model is the go-to choice for smaller spaces, perfect for studio apartments or small homes with 1-2 bedrooms. This compact powerhouse delivers quick hot water and efficient heating without taking up too much space. Its quiet operation is a bonus for open-plan living areas.

Ideal Logic Plus 30kW combi-boiler is ideal for medium-sized homes

For medium-sized homes with 2-3 bedrooms and multiple bathrooms, the 30kW version offers more power to meet higher demands. It provides ample heating and hot water for families while keeping energy bills in check.

Ideal Logic Plus 35kW combi-boiler is ideal for large homes

This model is built to handle the demands of 4+ bedroom homes or properties with multiple bathrooms. It ensures you’ll never run out of hot water, even during those busy morning rushes.

Ideal Logic Plus combi-boiler: Efficiency 

• A-rated for both heating and hot water efficiency
• Up to 94% energy efficiency
• Fully modulating operation, adjusting output based on demand
• Energy Saving Trust
• Low energy pump for reduced electrical usage

Ideal Logic Plus combi-boiler: Prices

• Ideal Logic Plus 24kW – £847
• Ideal Logic Plus 30kW – £1,019
• Ideal Logic Plus 35kW – £1,039

Ideal Logic Plus combi-boiler: Warranty

• Standard 7-year parts and labour warranty
• 10-year warranty on the heat exchanger

Best for Saving on Your Energy Bill: Worcester Bosch Greenstar 4000

The Greenstar 4000 combi boiler range comes in two models: 25kW and 30kW. 

While these new compact boilers might cost a bit more upfront, they’re A-rated for efficiency, which means you could save up to £600 on your yearly energy bills. So, even though you’re paying more at the start, you might end up saving money in the long run.

Greenstar 4000 25kw combi-boiler is ideal for small homes and flats 

With the ability to heat up to 10 radiators, the 25kW version is ideal for small homes and apartments.

However, we must mention that you get a 10.5 litres per minute flow rate, so it’s only suitable if you have one washroom and use minimal water. Otherwise, this would be a wrong choice as it is the lowest output-generating model.

Greenstar 4000 30kW combi-boiler is ideal for medium-sized homes

For medium-sized homes with 3-4 bedrooms, the 30kW version steps up to meet higher demands. It can handle up to 15 radiators and offers a flow rate of 12.3 litres per minute, making it suitable for properties with multiple bathrooms.                              

Greenstar 4000 combi-boiler: Efficiency 

• A-rated for both heating and hot water efficiency
• Up to 94% energy efficiency
• Features innovative “QuickTap” water-saving technology
• Modulating burner adjusts output to match your home’s heating demand
• Low energy pump reduces electrical consumption

Greenstar 4000 combi-boiler: Prices

• Greenstar 4000 25kW – £1,162
• Greenstar 4000 30kW – £1,389

Greenstar 4000 combi-boiler: Warranty

• Standard 5-year warranty
• Up to 10-year extended warranty
• 10-year warranty on the primary heat exchanger

How to Choose the Best Small Combi Boiler

When buying a boiler, you should look for several things in addition to the price and a high efficiency rating to avoid unexpected costs down the road.

Installation

The installation process of a new boiler in your home should be hassle-free and convenient. If you select a high-quality unit from a reputable manufacturer, thanks to their expertise, this process won’t take long.

Don’t forget to ask about installation costs for specific models. While it might be tempting to go for the cheapest option, remember that a high-quality boiler may have higher installation costs but could save you money in the long run.

Boiler Size

A big boiler uses extra fuel and is more expensive to run, so make sure to select the right size to meet your home’s hot water needs.

We recommend consulting a Gas Safe licensed engineer since they consider various elements, such as the number of radiators, bathrooms, and occupants, as well as the quality of insulation in the home. The standard size range for domestic boilers is 14–35kW.

Heat Control

Check if the boilers you’re considering are compatible with your preferred heating controls. Some models are compatible with cutting-edge WiFi-enabled intelligent controls and can be operated remotely from anywhere using an app on your smart devices.

Others are available with simple manual controls or programmable thermostats that you can configure to turn on and off at specific times.

Fuel Source

The fuel source used in your home may influence your options. Natural gas, oil, LPG (Liquified Petroleum Gas), and electricity are the four most popular fuel types for boilers.

The majority of homes in the United Kingdom use natural gas. However, it’s essential to comprehend how natural gas codes affect your installation choices. We recommend discussing these restrictions with your specialist or natural gas provider.

FAQs

What are the dimensions of small combi boilers?

The Worcester Bosch combi boiler CDI is the smallest combi boiler system currently available. It has a diameter of 280mm, a breadth of 390mm, and a height of 690mm.

Because of its size, it’s an excellent alternative for studio apartments and tiny homes and can easily be stashed away in kitchen cabinets.

How long should a compact combi boiler last?

Most modern gas boilers last between 10 and 15 years if purchased from a reputed company and kept in good condition. If your current boiler system is approaching this age, it might be time to consider an upgrade.

Although there is no specific rule for when you should replace a boiler, it all depends on the boiler manufacturer, how much you’ve used it, and how well you’ve taken care of it.

What compact gas boiler size to buy?

Most compact gas boilers have a power output of under 25 kW, perfect for studio apartments, flats, and smaller homes. However, this depends on the number of occupants and radiators in the home and the usual water usage.

A 25kW boiler can usually handle a one or two-bedroom home. For less frequent use, a boiler with a lower output might suffice. Larger homes or homes with higher water usage require 30kW or 35kW boilers, depending on the number of bedrooms and bathrooms.

Can I install a compact combi boiler of my own?

A DIY installation is not advised if you are not qualified by law or unfamiliar with how to perform this operation.

While it’s legal to perform gas work independently, you can only install a combination boiler if you have the necessary Gas Safe qualifications.

Boiler installation companies ensure all their employees have proper credentials or have undergone specialised training.

Some UK boiler manufacturers prefer you invest in getting their expert staff for installation. Not only is it illegal to install the boiler yourself, but you may also lose the warranty. So, it’s better to hire a Gas Safe professional to have your boiler installed correctly.

Final Thoughts

Boiler Central always tries to save you from wasting time deciding on the best combi boiler, so we hope we’ve provided all the information about compact boilers you need to navigate the various models available.

To recap, the Viessmann Vitodens 050-w is best for overall value and energy efficiency. The Worcester Bosch Greenstar CDI Compact offers advanced features and the most compact size. The Ideal Logic Plus is a cost-effective option without compromising on quality, while the Greenstar 4000 is best for homeowners looking to save on their energy bills in the long run.

Want to know exactly how much your new Viessmann boiler will cost? Contact us today, and we’ll break down all the costs for you.