Best Combi Boilers Under 40kW

Finding the right boiler for your home can seem like an impossible task, especially when there are so many different brands and models available on the market that each boast incredible features.

That’s why we’ve kept it short and simple by compiling a list of all the best combi boilers under 40kW and their features.

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1. Viessmann Vitodens 050-W 35kW

With compact dimensions, low weight and quiet operation, the attractively priced Vitodens 050-W 35kW is a mid-range combi boiler that can integrate effortlessly into any living space without compromising on quality; making it ideal for both new build homes and modernisations. 

Key Boiler Features:

• Efficiency: 92% (A-Rated) 

• Stainless steel heat exchanger

• Hot Water Flow Rate: 14.5 l/m

• User-friendly LED display for easy operation

• Quiet operation thanks to low fan speed

• Wi-Fi interface

• Which? Best Buy Gas Combi Boilers September 2021

• Compact size: W 400mm, D 350mm, H 707mm

• Warranty: 10 Years on parts and labour with iHeat

One of the most significant benefits of the Viessmann Vitodens range is the use of a stainless steel Inox-Radial heat exchanger as this is much more durable and provides a high resistance to corrosion in a wide variety of pH levels than an aluminium heat exchanger, which is used by many other boiler brands.

As winner of the Which? Best Buy Gas Combi Boilers September 2021, it’s evident that this is a much loved, reliable combi boiler. 

Owners of the Viessmann Vitodens 050-W scored the boiler highly for its reliability and good build quality. Owners were left satisfied after buying and engineers voted it as generally easy to service and repair.

Which? couldn’t find any major cons, other than that some replacement parts can be tricky to get hold of.

A study also found that faults in Viessmann boilers are infrequent, with around three quarters experiencing no faults at all within the first six years of ownership.

2. Viessmann Vitodens 100-W 35kW

Efficient, quiet and affordable, the Vitodens 100-W 35kW combi boiler is our most popular solution available at iHeat, thanks to its incredible heating abilities which are packed into a compact frame.

Featuring innovative technology and services combined with reliability and longevity and comes ready for smart technology, this boiler will help you to optimise your heating and save on energy costs; a win-win. 

Boiler Features:

• Efficiency: A-Rated 

• ErP Heating Seasonal Efficiency of 94%

• Stainless steel heat exchanger

• Hot Water Flow Rate: 12.4 l/m

• User-friendly LED touchscreen for easy operation

• Quiet operation thanks to low fan speed

• Wi-Fi interface

• Which? Best Buy Gas Combi Boilers September 2021

• Compact size: W 400mm, D 350mm, H 707mm

• Warranty: 10 Years on parts and labour with iHeat

As we mentioned earlier, the entire Vitodens range uses high quality stainless steel Inox-Radial heat exchangers which efficiently convert the supplied energy into heat. 

The Vitodens 100-W in particular uses a wide range of high quality brass and copper internal components, making it incredibly reliable and longer lasting.

3. Ideal Logic+ 35kW

The Logic+ is Ideal’s most popular boiler thanks to its compact dimensions and powerful, yet efficient, heating and hot water abilities, making it ideal for medium sized homes.

Boiler Features:

• A-Rated for efficiency

• Aluminium heat exchanger

• Hot water flow rate 12.5 / 14.5 litres per minute

• Compact dimensions W 395mm D 278mm H 700mm

• Easy-to-use fully backlit LCD

• Frost protection

• Quiet Mark Certified

• Winner of Queen’s Award for Enterprise 2013

• Good Housekeeping Reader Recommended in 2013 and 2017

• Warranty: 10 years on parts and labour with iHeat

The Ideal Logic+ 35kW combi is a fantastic boiler with a wide range of highly efficient features for an affordable price, helping you to make savings all around. 

As the winner of the Queen’s Award for Enterprise, Product of the Year and Good Housekeeping Reader Recommended, there’s no doubt this boiler can provide you with an effective and reliable heating solution.

4. Alpha E-Tec 33kW

The Alpha E-Tec 33kW is one of our best selling combi boilers thanks to its great affordability without compromising on quality.

The E-Tec is also Alpha’s most compact model yet, making it perfect for small and medium sized homes and fitting in standard kitchen cupboards.

The entire E-Tec combi boiler range features brand new stainless steel heat exchangers and zinc plated expansion vessels, making them highly robust, more corrosion resistant and much longer lasting. 

The E-Tec 33kW also has a high-efficiency pump which helps to deliver impressive hot water flow ratings of 14.1 litres of hot water per minute and the single electrode drive charge is very easy to access, meaning your boiler will be easy to control and manage after installation.

Boiler Features:

• Stainless steel heat exchanger

• High efficiency pump and hydroblock assembly

• Easy-access dry-change NTCs

• Combined condensate and pressure relief valve connection

• Zinc plated expansion vessel to prevent corrosion

• Rated A (89%) for energy efficiency

• Compact dimensions: W 440mm, D 255mm, H 712mm

• 10 Year Warranty with iHeat

• 14.1 litres/minute

5. Alpha E-Tec Plus 38kW

The E-Tec Plus 38kW is similar to the E-Tec but is physically larger in size and has a few extra benefits, such as copper pipe tails with isolation valves, an integrated filling loop and a control panel and bottom cover. 

They’re also slightly more efficient than the standard E-Tec, with an A Rating of 93%, helping you to make big savings on your home heating bills.

This boiler can keep your home at the right temperature all year long without costing you an arm and a leg to do so thanks to its low purchase price and high efficiency ratings.

Boiler Features:

• Stainless steel heat exchanger

• High efficiency pump and hydroblock assembly

• Easy-access dry-change NTCs

• Combined condensate and pressure relief valve connection

• Zinc plated expansion vessel to prevent corrosion

• Rated A (89%) for energy efficiency

• W 440mm, D 255mm, H 712mm

• 10 Year Warranty with iHeat

• 15.9 litres/minute

• Copper pipe tails with isolation valves

• Integrated filling loop

• Control panel and bottom cover

6. Worcester Bosch Greenstar CDI Compact 36kW

The Worcester Bosch Greenstar CDI Compact 36kW is an incredibly powerful boiler in a compact unit, meaning it can deliver fantastic heating and hot water all throughout your home, all from inside a standard kitchen cupboard.

Boiler Features:

• Rated A for Efficiency (91%)

• Aluminium Heat Exchanger

• Hot Water Flow Rate 14.7 l/m

• Frost protection

• Wide choice of controls for greater comfort and economy

• Low energy pump to reduce electrical waste

• Compact dimensions W 390mm, D 280mm, H 680mm

• Warranty: 10 Years on parts and labour with iHeat

7. Worcester Bosch 8000 Style 35kW/40kW

The Worcester Bosch 8000 Style 35kW and 8000 Style 40kW is one of the most premium models on the market by far, featuring a brand new modern design packed full of innovative new features that help keep your home warm and your boiler working at its best.

• Efficiency: A-Rated 94% (35kW) 91% (40kW)

• Hot Water Flow rate 14.3 l/m (35kW) 14.7 l/m (40kW)

• Compact Dimensions: W 390mm, D 280mm, H 680mm

• Available in black or white

• Easy-to-use full colour display

• Wireless connectivity

• Warranty: 10 Years on parts and labour with iHeat

40kW Boiler FAQs

How Many Radiators Can a 40kW Combi Boiler Run?

A 40kW combi boiler can power up to 20 radiators in your home.

How Many Bedrooms Can a 40kW Combi Boiler Heat?

A 40kW combi boiler is most suitable for homes with 3-4 bedrooms.

How Many Bathrooms Can a 40kW Combi Boiler Service?

In order to meet the demand for heating and hot water, a 40kW boiler is most suitable for homes with 2-3 bathrooms.

Which Size Boiler is Right for Your Home?

Looking for a Boiler Under 40kW?

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