James Elston

Published April 9, 2024

Small combi boilers, as the name suggests, pack a powerful punch in a significantly smaller frame. A small combi boiler can be perfect for smaller properties – it might even fit into your kitchen cabinet.

However, if your new boiler is too small, it’ll need to work twice as hard to run your central heating system, and if it’s too big it’s just a waste of space and energy. That’s why choosing the right size boiler for your home is so important.

Both small gas combi boilers and electric combi boilers boast improved efficiency due to their innovative technology and design, reducing energy consumption and running costs.

So, let’s have a look at some of the top-rated small boilers for homes that you can find on the market in 2024.

The 5 Top-Rated Small Combi Boilers In 2024

These are the best models of combi boilers available on the market in the UK, according to Eco Happy. Based on your needs, you can make an informed decision on what the best small combi boiler is for you and your home. 

1. Worcester Bosch Greenstar 4000


  • Efficiency: 93% (A-rated)
  • Variants: 25kW and 30kW
  • Guarantee: 10-year guarantee
  • Dimensions: Width 400 mm, Height 724 mm, Depth 310 mm


  • Incredibly quiet operation
  • A ‘Quick Tap’ water-saving function which reduces water wastage and promotes eco-friendly usage
  • Full-colour text display for a satisfying user experience
  • Wireless connectivity with the Bosch EasyControl


The Worcester Bosch Greenstar 4000 is available in both 25kW and 30kW models, which gives it a good amount of versatility. If you have a smaller home with 10 radiators and one bathroom, then you can opt for the 25kW and if your home has 15 radiators then the 30kW model will suit you nicely. In fact, the 30kW model is one of the best 30kW boilers on the market.

It has a 93% efficiency rating which means it can save you money on your energy bills while also reducing your home’s carbon footprint. Plus, it can be integrated with the Bosch EasyControl smart thermostat to give you full control over your heating schedule.

We think it’s the best small combi boiler around – but don’t just take our word for it. The Worcester Bosch Greenstar 4000 has won the Which? Best Buy Award for ten years in a row from 2014 to 2023. 

2. Viessmann Vitodens 050-W


  • Efficiency: 92% (A-rated)
  • Variants: 3.2-19kW, 25kW and 30kW
  • Guarantee: 7 years as standard (can be extended to 10 years)
  • Dimensions: Depth 300 mm, Width 400 mm, Height 700 mm


  • Inox-Radial heat exchanger for maximum durability
  • MatriX-Plus burner for clean combustion and high levels of efficiency
  • Integral WiFi interface which can be paired with Viessmann apps
  • Power-saving circulation pump


The Viessmann Vitodens 050-W is even more versatile than the top-rated boiler on our list. It’s available with outputs of 3.2-19kw, 25kW, and 30kW, meaning it’s a great choice for very small to medium-sized homes. 

Its stainless steel Inox-Radial heat exchanger gives this boiler plenty of durability and means that it should last for a long time. The reason it’s second on our list is that it has a slightly lower efficiency rating than the Worcester Bosch Greenstar 4000 and its standard warranty isn’t as long. 

If you’re looking for a combi boiler for a larger home, then we’d recommend the more powerful Viessmann Vitodens 200-W 40kW, which we consider one of the best 40kW combi boilers currently available.

3. Worcester Bosch Greenstar CDi Compact


  • Efficiency: 92% (A-rated)
  • Variants: 28kW and 32kW
  • Guarantee: 10-year warranty
  • Dimensions: Width 390 mm, Height 680 mm, Depth 278 mm (may vary depending on the specific model)


  • Built-in frost protection
  • Low-energy pump for reduced electrical usage
  • User-friendly interface
  • Clear temperature display and simple boiler control knobs


The Worcester Bosch Greenstar CDi Compact is available with outputs of 28kW and 32kW, so it’s more suited to slightly larger homes than the first two boilers on our list. For example, if your home has 15-20 radiators then the 32kW model will be able to supply you with heat and hot water easily. 

Its warranty and efficiency are great but it is lacking some of the more high-tech features of our previous two inclusions. Still, it has a clear user interface and built-in frost protection. So, it comfortably takes third place on our list. 

4. Ideal Logic Plus


  • Efficiency: 92% (A-rated)
  • Variants: 24kW, 30kW, and 35kW
  • Guarantee: 7-year warranty
  • Dimensions: Height 700 mm, Width 395 mm, Depth 278 mm


  • Quiet Mark certified which means it doesn’t produce disruptive noise levels
  • Built-in frost protection
  • Fully backlit LCD interface


The Ideal Logic Plus is highly versatile with three different output ratings available. This means it’s an ideal option if you have a small apartment or a medium-sized house. It also produces little noise when running which is why it’s been awarded the Quiet Mark. Once it’s installed, you won’t even notice it working away in the background. 

It has a fully backlit LCD interface which is really easy to use and the unit can slot into a kitchen cupboard. If you’re looking for a discreet yet powerful small combi, then this is an excellent choice. Ideal boiler prices also tend to be very competitive, and installation costs for small combis are relatively low due to the ease of installing them.

5. Worcester Bosch Greenstar Style 8000


  • Efficiency: 94% (A-rated)
  • Variants: Available in various sizes (e.g. 30kW, 40kW, 50kW)
  • Guarantee: Warranty duration may vary depending on specific model and retailer
  • Dimensions: Height 780mm, Width 440 mm, Depth 365 mm


  • Optional Intelligent Filling System
  • Wireless connectivity with the Bosch EasyControl
  • Full-colour display


The Worcester Bosch Greenstar Style 8000 is available with power outputs of 30kW, 40kW, and 50kW. The more powerful models can supply a home with 15 to 20 radiators and two or more bathrooms. Like the top-rated boiler on our list, it can also be paired with the Bosch EasyControl and its full-colour display makes its interface easy to use. 

The only issue is that the warranty information for this boiler is a little vague and can vary quite widely depending on the supplier. Still, it’s a small combi that packs a massive punch. 

As an honourable mention, the Worcester Bosch Greenstar 2000 is also a brilliant combi boiler and is considered one of the best electric combi boilers on offer by Worcester Bosch.

How We Chose The Best Small Combi Boilers

Here’s how we compiled our list of the best 5 small combi boilers.


We looked for positive customer reviews on sites like Trustpilot that mentioned the reliability of the boilers we were assessing. We wanted to see how they performed in the real world and how often customers had to call out engineers for repairs. 


We analysed what customers said about their energy bills since they’ve been using the boilers on our list. If a boiler was highly efficient and had helped to reduce their bills, then it gained points and had more chance of being included. 

Independent testing bodies

We closely analysed the test results from impartial testing bodies like Which? to see how boilers performed. Sites like this are a more useful source of data than manufacturer sites which are obviously more focused on marketing than providing unbiased information. 

How To Choose The Best Small Combi Boiler For You

Several key factors deserve your attention to ensure you choose the best small combi boiler for your needs. Here are some of the most important aspects to consider:

1. Which? Best Buy Awards: Recognising consistently reliable boilers, the Which? Best Buy Awards offer valuable guidance for consumers. Opting for a new combi boiler with this prestigious accolade assures long-term performance and peace of mind.

2. Warranty: A comprehensive warranty protects you against unexpected repairs and breakdowns. Longer warranties, typically 10 years or more, indicate manufacturer confidence in the product’s quality and durability.

3. Efficiency ratings: Look for energy-efficient compact boilers with high ErP ratings (such as A or A+) to maximise energy savings, lower the running costs of your central heating, and reduce your impact on the environment.

4. Parts availability: Ensure easy access to spare parts and components for future maintenance and repairs. Choosing an electric or gas combi boiler from a popular brand with readily available parts minimises inconvenience and ensures prompt fixes.

5. Home size: The size of your home is an important factor when choosing a combi boiler as it must have enough power to meet your heat and hot water demands. For instance, if your home has up to 10 radiators and one bathroom then a 20kW combi will suffice. If your home has up to 20 radiators and two bathrooms, a combi with an output rating between 35-42kW will be needed.

6. Features: Pay close attention to the specific features a boiler offers. In particular, look for boilers that can be integrated with smart controls. 

7: Brand reputation: You should also read reviews of boiler brands to find out what customers say about their customer service and the services of their engineers. 

8: Budget: Consider how well the price of a boiler fits into your budget. Generally, you should always try and buy the most expensive boiler you can afford, as higher-quality boilers tend to require fewer repairs which saves you money over time. 

If you can find a new combi boiler that ticks all those boxes and benefits your pocket and the environment (like the Bosch Greenstar CDI compact boiler) then you’re good to go. Keeping your central heating running shouldn’t come at the cost of the environment.

Compact vs. Small Combi Boilers

Small combi boiler 

It’s not what you’re thinking – this isn’t the mini marvel you can tuck away in a kitchen cabinet. In the world of boilers, “small” refers to the power it packs, measured in kilowatts (kW). Think of it like a car engine – smaller engines deliver less power, perfect for smaller spaces and more limited heating requirements.

So, a “small boiler” is simply one with a lower output, ideal for cosy homes with modest domestic hot water demands. These often fall within a specific kW range, but remember, “small” is relative – it’s all about finding the best fit for your needs. Still, small combi boiler installation is much more straightforward than the complex installation process for larger units like system boilers. 

Compact combi boiler 

On the other hand, “compact” refers to the amount of space the boiler occupies. And this doesn’t mean miniaturisation, but rather a focus on slim, space-saving design. Think of it like a sleek sports car – powerful, but not bulky.

Compact combi boilers are designed to fit snugly into tight spaces (like kitchen cupboards) without sacrificing performance. This makes them ideal for smaller homes or anywhere where space is limited.

Combi Boilers With Different Output Ratings

Combi boilers come in a range of output ratings, measured in kilowatts (kW). This rating indicates the boiler’s heating capacity, determining how much warmth it can provide. Choosing the right output is crucial for optimal comfort and efficiency.

Navigating the power spectrum:

  • 20-24kW: These are petite powerhouses, ideal for small studios, apartments, and single-bathroom dwellings. Think of them as the nimble ninjas of the boiler world, perfectly suited for compact spaces and limited hot water needs.
  • 25-28kW: Moving up in size and power, these are reliable workhorses, perfect for slightly larger homes with moderate hot water needs. Imagine them effortlessly meeting the demands of two-bedroom houses and single-bathroom dwellings with multiple occupants.
  • 30kW and above: These are the behemoths, built for spacious homes with multiple bathrooms. Think of them as powerful locomotives, capable of pulling the heating and hot water needs of large families with ease.


How much does it cost to install a small combi boiler?

On average, it costs around £1,500 to £3,000 to have a small combi boiler installed by an engineer in the UK. This includes the price of the unit, the installation, and VAT. 

What is the smallest combi boiler you can get in the UK?

The smallest combi boiler you can get in the UK generally falls within the 20-24 kW range. This compact combi boiler is ideal for smaller homes with limited space and low hot water demands, such as apartments, studios, and flats. Smaller combi boilers also tend to be some of the cheapest combi boilers, making them ideal for budget-savvy homeowners.

The smallest boiler in the UK is the Intergas Compact ECO RF 24 – it’ll fit snugly inside any kitchen cupboard!

What boiler brands do plumbers recommend for small combis?

The small combi boilers from three different boiler brands come highly recommended by plumbers:

  • Viessmann: Known for their high-quality components, innovative design, and quiet operation.
  • Worcester Bosch: Praised for their reliability, long lifespan, and excellent customer service.
  • Vaillant: Offer a wide range of boilers with user-friendly controls and efficient operation.

Final Thoughts

Don’t be fooled by its name – a small combi boiler can power your central heating and provide you with hot water, all while minimising your carbon footprint. A quality small boiler with a long warranty and high ErP rating should keep running costs in check – and keep you snug in icy temperatures.

Whether you’re changing from a conventional boiler to a combi boiler, looking for a compact alternative to a system boiler, or simply replacing an old combi, we’re sure you’ll find what you’re looking for in our top 5 list. Ready to unlock the world of comfort and convenience a small combi boiler offers? Then contact Eco Happy for a small boiler quote – as one of the most reliable boiler manufacturers in the UK, we’ve got you covered.

James Elston

Boiler Expert

James Elston is the top boiler replacement and heating expert at Eco Happy. He has over 20 years of experience in the industry, focusing on Gas Safe boiler installations and offering home-heating and energy-saving solutions to homeowners across the UK. From sourcing the most energy-efficient combi boiler to providing specialist heating advice, James ensures that Eco Happy maintains the highest standards and best customer service.

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