Best combi boilers in the UK for energy efficiency (2023 guide)

Finding the right combi boiler for your home can make it a great investment. (Image credit: Adobe)

Combi boilers, also known as combination boilers, have become one of the most popular methods of powering central heating systems in the UK. This is largely due to their energy efficiency of over 90%, which not only saves money on bills but can also help homes to reduce their emissions compared to conventional boilers.

These boilers are also much smaller than older systems and heat water directly from the mains, which means you don’t have to worry about installing a bulky hot water storage tank in your home. This also boosts the boiler’s efficiency, as it only heats water as it’s needed rather than having to maintain a certain temperature in a tank.

Thanks to their growing popularity, there are dozens – if not hundreds – of different boiler models available today, each with its own specifications. In this guide, we’ve reviewed some of the best combi boiler models on the market.

• Ideal Logic+ Combination Boiler: Most affordable
• Vaillant ecoTEC exclusive Green iQ 835 Combi: Most energy efficient
• Baxi Platinum Combi Boiler: Easiest to install
• Viessman Vitodens 111-W B1LD-35 Storage Combi Boiler: Most powerful
• Worcester Bosch Combi Greenster 4000: Best for small homes

We reviewed the best combi boilers in the UK. Here’s a summary of what we found.

Ideal Logic + combi boiler: Most affordable

Image credit: Ideal Heating

• Warranty: Seven-year warranty for parts and labour, 10-year warranty on the heat exchanger
• Output rating: 24kW, 30kW and 35kW
• Efficiency rating: A
• Cost: £879–£1,011

The Ideal Logic + combi boiler is a perfect choice if your main concern is the cost. The boiler is quite affordable but still high quality, so you’ll still get value for money. As an award-winning combi boiler, the Ideal Logic+  holds a Queen’s Award and a Good Housekeeping award due to its quality. 

It has built-in frost protection and provides excellent energy savings. In addition, it holds a Quiet Mark accreditation, so it will perform quietly, making it ideal for kitchen installations. The  Ideal Logic+ combi boiler comes with a 10-year warranty on the heat exchanger and a seven-year warranty for parts and labour, so it’s durable.

Cost

The Ideal Logic+ combi boiler is budget friendly. According to online estimates, the typical price for the unit is £879–£1,011, not including installation. However, even with installation this is an affordable option.

Our recommendation

The Ideal Logic + combi boiler is affordable and comes with a reasonable warranty period that can compete with premium brands. It has a compact size which means it can fit in a standard kitchen cupboard. This combi boiler is ideal for houses with one to three bedrooms and a single bathroom. If you get this combi boiler for your home, you can save on your energy bills as well as the initial costs.

Vaillant ecoTEC exclusive with Green iQ combi boiler: Most energy efficient

Image credit: Vaillant

• Warranty: Five-year standard, 10 years if installed by an improved installer
• Output: 35kW or 43kW
• Efficiency rating: A
• Cost: £1,400–£1,920

If you’re looking for an environmentally friendly combi boiler in the UK, you can’t go wrong with a Vaillant ecoTEC exclusive Green iQ combi boiler. Vaillant has been making high-quality boilers for years and is known as one of the most energy-efficient brands, so you can save money on your energy bills while still getting a great boiler for your home.

The Vaillant ecoTEC Green iQ combi boiler is eco-friendly and 85% of its parts are recyclable. It’s a reliable and high-performance combination boiler that can heat large properties with up to 20 radiators. It comes with a guarantee of up to 10 years if you book a Vaillant Advance installer.

It’s compatible with the Vaillant vSMART™ control, which allows you to control your boiler from your smartphone or tablet. Additionally, it’s Quiet Mark approved, meaning it’s one of the quietest products, so you don’t have to worry about noise in your home. This combi boiler is ErP A rated for both hot water and heating efficiency.

Cost

The Vaillant ecoTEC exclusive Green IQ combi boiler range has a reasonable price, starting at £1,400. However, you have to factor in installation costs, which could take the total price to over £2,000.

Our recommendation

The Vaillant ecoTEC exclusive Green iQ combi boiler is a great option if you own a larger home with a high hot water demand. Despite this, it’s still one of the most energy efficient models on the market. It uses green IQ technology, which allows the boiler to modulate its output down to 10% at times of lower demand, helping you save money on your energy bills. It also has a 94% efficiency rating. It comes equipped with an extra-condense stainless steel heat exchanger, making it a great alternative for eco-conscious consumers. 

Like other combi boilers, it’s compact enough to fit in a kitchen cupboard. You can control its performance using a smart thermostat and mobile app for greater efficiency. To take advantage of the lengthy 10-year warranty, you must use a certified Vaillant installer. 

Baxi Platinum combi boiler: Easiest to install

Image credit: Baxi

• Warranty: 10-year parts and labour warranty
• Output: 24kW–40kW
• Efficiency rating: A
• Cost: Average £880–£1,150

The Baxi Platinum combi boiler is reliable and easy to install, making it a favourite with householders and installers. Built using top-quality brass components, this combi boiler has an output of up to 40kW providing 16.4 litres/minute hot water. 

Homeowners can top up the central heating system pressure without calling an engineer using the EasyFill valve. The boilers are compact, making them easy to install and fit in your home. Baxi boilers are energy efficient, with some models boasting SEDBUK Band A ratings. That means they could help lower your energy bills. 

Cost

On average, prices for the Baxi Platinum start at £880 for the 24kW unit and go up to £1,150 for the 40kW boiler, excluding installation.

Our recommendation

If you are going for the Baxi Platinum boiler in a larger house, we recommend the 40kW model because it has a high power output and provides 16.4 litre per minute flow. These boilers are not too costly and have a lengthy warranty period. It also has a high energy efficiency rating if you are looking to save on your energy bills. 

The Baxi Platinum boiler can power homes with up to two showers simultaneously. It’s suitable for different households because of the reliable components. Unfortunately, it can be slightly bulky compared to the other combi boiler models, so you may have to install it in a loft or garage. 

Viessmann Vitodens 111-W Storage combi boiler: Most powerful

Image credit: Viessmann

• Warranty: Up to 12 years guarantee on parts and labour
• Output: 26kW–35kW
• Efficiency rating: A
• Cost: £1,520–£1,630

Viessmann manufactures a wide range of combi boilers to meet any property’s heating and hot water demands. The Viessmann Vitodens 111-W combi boiler in particular is a top choice because it has an energy efficiency rating of 98%.

This combi boiler has a cylinder loading system (CLS) and 46L integrated stainless steel storage tank, which has the capacity to fill a standard bath in around eight minutes while supplying water to other taps simultaneously. It has a high flow rate of 18 litres/minute, making it suitable for a family home with high water needs.

You can get the 25kW or the 32kW option, which is slightly larger and more suitable for larger homes with several bathrooms and radiators. The combi boiler is rated A for energy efficiency. It has low carbon dioxide emmisions, reducing the impact on the environment. 

Additionally, it is equipped with a user-friendly LED touch screen for easier operation. When you install it, you can use the optional easy-to-install ViCare thermostat and smartphone app. This will help you optimise your heating environment and save energy costs remotely via your phone.

Cost

According to online estimates, the Viessmann Vitodens 111-W combi boiler typically costs about £1,520–£1,630. The initial price can be quite costly compared to other brands but matches up to the boiler’s quality and engineering.

Our recommendation

The Vitodens 111-W combi boiler is a good choice if you need a more powerful boiler. It’s also highly efficient, so it will help you reduce your energy bills. If you get the 32kW model, you can meet the heating demands of a family home with multiple radiators. This boiler is perfect if your house has a high demand for hot water.

Despite being powerful, it’s still compact enough to fit into a cupboard or small storage space. It’s also durable thanks to the warranty period. It has a five-year standard guarantee, which can be extended by an additional seven years if installed by a Viessamann installer. However, if you are looking for a budget friendly option, this combi boiler might be slightly expensive.

Worcester Bosch Greenstar 4000 combi boiler: Best for small homes

Image credit: Worcester Bosch

• Warranty: 10-year guarantee when installed by a Worcester installer
• Output: 25kW–30kW
• Energy efficiency: A
• Cost: £985–£1,050

This UK-based boiler manufacturer has been active since 1962 and established itself as a renowned household name with its wide range of high-performance boilers that come in different sizes, styles and price points for any home. The Worcester Bosch Greenstar 4000 combi boiler is their most popular model yet.

The Worcester Bosch Greenstar 4000 is an excellent choice if you’re looking for an eco-friendly option, as it has a low carbon footprint and is designed to be highly reliable and energy efficient. It can run on a 20% hydrogen blend, meaning it’s ready for potential changes in the UK’s fuel supply. It also has a wide power range that can reduce gas consumption and energy bills. 

This boiler is energy efficient, with an A-rating. Additionally, the Greenstar 4000 is quieter and compact, making it ideal for homes with limited space. It’s also compatible with Worcester Bosch controls and third-party Wi-Fi smart controllers.

Cost

On average, the typical price of this combi boiler is £985 to £1,050 excluding installation costs.

Our recommendation

The Worcester Bosch Greenstar 4000 powerful and would be ideal for a house with multiple bathrooms and several water outlets. The Greenstar 4000 has a 10-year warranty period, offering value for money.

Before selecting a combi boiler, examine your household needs. With this in mind you can choose the brand and model that will work for your home. Ensure that you compare factors such as reliability, warranty period, cost, energy efficiency, eco-friendliness and output rating before making your order.

In order to conduct this research, we used a scoring system based on the key factors to consider when choosing a combi boiler. We rated each brand based on the 100-point scoring system.

• Energy efficiency for each boiler for a total score of 15 points;
• The power outputs of each boiler with a total score of 10 points;
• The warranty period for a total score of 15 points;
• The sound power for each boiler with a total score of 5 points;
• Compactness of the boiler for a total score of 15 points;
• The average price for each boiler for a total score of 15 points;
•  Manufacturer’s level of experience for a total score of 10 points; and
• The reputation of the company on review sites for a total score of 15 points.