Looking for the best combi boiler in 2025? At Heatable, our team of Which?-approved gas engineers has reviewed and ranked the top models based on efficiency, reliability, and value.
Drawing on our experience installing over 50,000 boilers across the UK, we’ve curated this guide to help you find the perfect combi boiler for your home, whether you’re after the best all-around option, the most budget-friendly, or the most efficient.
Quick Take: Top Combi Boilers for 2025
At Heatable, we know choosing a new combi boiler can feel like a slog - time and stress you don’t need! In a rush? Save this page for later and skim this snapshot of our expert guide.
With countless combi boilers out there - each with varying efficiencies, warranties, and costs - picking the right one for your UK home can be tricky. The best choice depends on your setup: think property size, radiators, showers, and hot water demands.
Our biggest tip? Zero in on the warranty. A flimsy 1–2 year guarantee signals a boiler might leave you in the lurch. We only fit boilers from the best brands, all backed by 7–12 year warranties in your fixed price. Our go-to brands are:
Worcester Bosch
Viessmann
Vaillant
Alpha
Our top picks from these brands include:
Worcester Bosch Greenstar 4000 (Best All-Rounder)
Viessmann Vitodens 100-W (Most Energy-Saving)
Worcester Bosch Greenstar 2000 (Best for Small Spaces)
Vaillant EcoTec Plus (Ideal for Bigger Homes)
Alpha E-Tec NX (Top Budget Option)
Want a hassle-free way to find the perfect boiler? Our 60-second form has you covered. Answer a few quick questions about your home, and we’ll match you with a reliable combi boiler - whether you’re in a cosy flat or a sprawling detached house.
What is a Combi Boiler?
Combi boilers are the most popular type of boiler in the UK, primarily because they provide both heating and hot water from a single, compact unit. Ideal for most homes, combi boilers are efficient and space-saving solutions.
Prefer video? Check out our YouTube video review of the best combi boilers:
What Makes a Combi Boiler the Best?
The best combi boilers excel in:
Efficiency: High ratings (e.g., 98% efficiency) save on energy costs.
Reliability: Long warranties and strong customer reviews signal durability.
Value: Balances upfront cost with long-term savings.
Aftercare: Quality support ensures peace of mind.
How We Chose the Best Combi Boilers for 2025
Our selection process, led by expert gas engineers, evaluated:
Warranty Period: Longer warranties indicate manufacturer confidence.
Efficiency Ratings: Higher ratings mean lower bills.
Customer Reviews: Insights from 10,000+ homeowners via Which? surveys.
Brand Reputation: Awards like the Which? Best Buy signal quality.
Aftercare Services: Reliable maintenance support.
Price vs. Value: Balancing cost with performance.
Best Combi Boilers of 2025: Detailed Reviews
Below is our carefully curated selection of the best combi boilers from top UK manufacturers.
These models stand out for their exceptional customer reviews, long warranties, technical superiority, energy efficiency, robust heating capabilities, and award-winning aftercare support.
We prioritised brands with industry-leading support, as reliable aftercare is crucial when issues arise.
#1 Worcester Bosch Greenstar 4000 – Best All-Around Combi Boiler
Key details:
Warranty: 10 years (via Heatable)
Efficiency: 94% (A-rated)
Output: 25–30 kW
Flow Rate: 10.5–12.3 L/min
Price: From £1,152.99
Why It’s the Best: The Worcester Bosch Greenstar 4000 is our top pick for 2025, thanks to its 14 consecutive Which? Best Buy Awards, a 4.7/5 Trustpilot rating (17,000+ reviews), and smart home compatibility with Hive, Nest, and tado°. It’s quiet, compact, and perfect for small to medium homes.
Pros:
Quieter than many competitors, ideal for noise-sensitive environments.
Works with popular smart home systems like Hive, Nest, and tado°.
10-year parts and labour guarantee through Heatable.
Excellent customer support and aftercare services.
Small footprint, fits easily in tight spaces.
Cons:
It is more expensive upfront compared to budget models like Alpha or Ideal.
Best suited for small to medium-sized homes, not ideal for large homes.
Lacks some of the advanced diagnostics features found in Viessmann models.
The image above shows a Worcester Bosch 4000 installed by the Gas Safe engineers here at Heatable. Get your free quote from us here.
"The aftercare service offered by the manufacturer is a key factor in choosing a new boiler as you want to know they will be fixed promptly without any issues". - Allen Hart, Gas Safe Engineer.
#2 Viessmann Vitodens 100-W – Most Efficient Combi Boiler
Key details:
Warranty: 12 years (via Viessmann-trained engineers)
Efficiency: 98% (A-rated)
Output: 26–35 kW
Flow Rate: Up to 14.1 L/min
Price: From £900
Why It Stands Out: With an industry-leading 98% efficiency, the Viessmann Vitodens 100-W saves on energy bills. It offers Wi-Fi connectivity and a stainless steel heat exchanger for durability.
Pros:
Includes features like Wi-Fi connectivity and smart home compatibility.
Stainless steel heat exchanger enhances longevity and reliability.
Offers up to 12 years of warranty when installed by a Viessmann-trained engineer.
A-rated for energy efficiency, capable of up to 98% efficiency.
Cons:
More expensive upfront compared to budget models like Alpha or Ideal.
While compact, it may still be slightly larger than some other models, limiting placement options.
Fewer output ratings compared to some other models.
Advanced features may require a more knowledgeable user or a professional setup.
The image above shows a Viessmann Vitodens 100-W installed by the team here at Heatable. Get a free quote from us here.
"What sets it apart is its impressive connectivity, allowing for remote access to the boiler, performance monitoring, and the ability to diagnose potential faults. This feature is a significant advantage not only for businesses but, more importantly, for our valued customers.” - Phil Cox, former Director of Sales, British Gas.
#3 Worcester Bosch Greenstar 2000 – Best Value for Small Homes
Key details:
Warranty: 6 years (extendable)
Efficiency: 94% (A-rated)
Output: 25–30 kW
Flow Rate: Up to 12 L/min
Price: From £750
Why It’s Great: The Greenstar 2000 is Worcester Bosch’s quietest and most affordable model, designed for small homes. Its compact size fits in kitchen cupboards, and it’s backed by Worcester’s strong reputation.
Pros:
Lower upfront cost compared to other Worcester Bosch models like the 4000.
Slim and compact, making it suitable for small spaces like kitchen cupboards.
Operates quietly, making it ideal for smaller homes or flats.
Backed by Worcester Bosch’s strong reputation for reliability.
Cons:
Standard 5-6 year warranty, which is shorter than the 10-year warranty offered by higher-end models.
Lacks some of the advanced features and smart technology compatibility found in more expensive models.
Lower water flow rate compared to more powerful models like the Worcester Bosch 4000.
Less comprehensive aftercare options compared to premium models.
#4 Vaillant EcoTec Plus – Best for Larger Homes
Key details:
Warranty: 10 years (via Heatable)
Efficiency: 94% (A-rated)
Output: 25–38 kW
Flow Rate: Up to 15.9 L/min
Price: From £1,100
Why It’s a Top Pick: The Vaillant EcoTec Plus offers powerful performance for larger homes, with a high flow rate and Quiet Mark certification for low noise.
Pros:
Ideal for larger homes, offering powerful heating and hot water output.
ErP A-rated for both heating and hot water efficiency.
Quiet Mark certified, ensuring low noise levels.
Compatible with vSMART technology for remote control.
Cons:
More expensive than budget models like Alpha E Tec NX or Ideal Logic+.
Lacks the advanced diagnostic features found in Viessmann Vitodens models.
It may be more powerful than needed for smaller properties, leading to inefficiency.
Larger in size compared to Worcester Bosch Greenstar 4000, making it harder to fit in tight spaces.
#5 Alpha E-Tec NX – Most Affordable Combi Boiler
Key details:
Warranty: 10 years (via Heatable)
Efficiency: 93% (A-rated)
Output: 26–33 kW
Flow Rate: Up to 14.1 L/min
Price: From £700
Why It’s a Great Value: The Alpha E-Tec NX combines affordability with quality, featuring a stainless steel heat exchanger and a slim design.
Pros:
Lower upfront cost compared to premium models like Vaillant or Worcester Bosch.
Slim design, making it easy to fit in small spaces like kitchen cupboards.
Stainless steel heat exchanger enhances durability compared to aluminium.
Up to 10 years, offering good coverage for peace of mind.
Cons:
Less established than top-tier brands like Worcester Bosch or Vaillant.
Fewer output options (26 and 33 kW) compared to other brands.
Lower flow rate compared to more powerful models like the Vaillant EcoTec Plus.
Lacks some of the advanced technology found in higher-end models.
Comparison Table: Best Combi Boilers of 2025
Model | Best for | Efficiency | Output (kW) | Flow Rate (L/min) | Warranty | Price | Which? Award |
Worcester Bosch 4000 | All-Around | 94% | 25-30 | 10.5–12.3 | 10 years | £1,152.99+ | Yes |
Viessmann Vitodens 100-W | Most Efficient | 98% | 26-35 | Up to 14.1 | 12 years | £900+ | Yes |
Worcester Bosch 2000 | Small Homes | 94% | 25-30 | Up to 12 | 6 years | £750+ | Yes |
Vaillant EcoTec Plus | Large Homes | 94% | 25-38 | Up to 15.9 | 10 years | £1,100+ | No |
Alpha E-Tec NX | Budget Friendly | 93% | 26-33 | Up to 14.1 | 10 years | £700+ | No |
Boiler Brands to Avoid
When picking a combi boiler, some brands are best avoided to keep your UK home warm in 2025.
For example, Ferolli scores a dismal 35% in Which? surveys, plagued by breakdowns and hard-to-find parts, with warranties as short as 1–5 years.
Vokera gets a 50% satisfaction score, with 1 in 10 owners hating it - think faulty parts, poor service, and 2-year warranties.
Here’s the golden rule: focus on the warranty. At Heatable, we’ve seen warranties reflect a boiler’s reliability - or at least give you peace of mind with parts and labour cover instead of hefty repair bills. A few years ago, 5 years was decent, but now 7–10 years is standard, with some hitting 12 years.
Avoid combi boilers with less than a 5-year warranty. You might save £100–200 upfront, but repairs (£150–300+) or replacing a cheap boiler will cost you more in the long run.
Go for trusted names like Worcester Bosch, Viessmann, or Vaillant for reliability and efficiency.
Why You Might Not Need the Best Combi Boiler
While top models offer great features, a mid-range boiler can suffice if:
You have a small home with low hot water needs.
Budget is a priority - models like the Alpha E-Tec NX offer great value.
Proper installation and maintenance can make even a budget boiler perform well.
Next Steps For Your New Boiler Journey:
When planning to install a new boiler for your home, there are several important factors to consider. Make sure to refer to the following guides to help you make informed decisions:
To dive deeper into these topics, head over to our advice section or check out our YouTube channel to learn more.
Get a Quote for a New Combi Boiler Today
If you’re aiming to get the best deal on a new boiler, consider getting a quote from us. Here’s why:
Gas Safe installation within 24 hours.
Thousands of satisfied customers with an average score of 4.9 on Trustpilot, surpassing the market leader.
Which? Trusted Trader: Heatable is proudly recognised as a Which? Trusted Trader.
Price match guarantee: We will match any like-for-like cheaper quote.
Flexible payment options, including interest-free finance*.
Up to a 12-year guarantee on selected boilers.
Fixed price guarantee: No hidden costs.
Save your quote and decide later.
Get an instant fixed price on a new boiler here.
To learn more about boilers, visit our advice section, check out our YouTube channel, or read customer testimonials here.
Heat Happy.
