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We’ve analysed data from 888 different boiler models across 21 different boiler brands to determine the best boilers in the UK. Weighting key features such as the average purchase price, output, efficiency, warranty length, and availability of replacement parts, we’ve ranked the top models.
Find out which boiler models are the best overall, which are the most reliable, and which are the best brands on the market – including Alpha, Vokera, and Vaillant.
To work out which boilers are the best, we scored them using what we deemed to be the most important metrics for homeowners. We scored 888 boiler models across 21 different companies using the following criteria:
*Warranty disclaimer: Each warranty is accurate as of the date of writing, but warranties are subject to change and may require registration, add-on terms or an accredited installer.
Here are the top 10 boiler models (highest performing model of each range), listed with their weighted scores out of a possible 100:
If you’re looking to upgrade your boiler, we carry out boiler installations across a range of leading brands.
All of the best boilers in the UK were decided using a scoring system that weights efficiency, warranty length, power output, readily available parts and average price.
Here are the top-scoring boiler ranges (scored out of 100) and their models, one from each category (combi, system and regular gas boilers).
While multiple models from the same range scored highly, we’ve listed only the highest-ranking model from each range to provide a clear, representative selection in our top boiler index.
Score 65.6/100
The Vokera Evolve C 42kW Combi boiler is the best overall boiler – scoring 65.6 out of a possible 100. This Vokera model achieved the best score across efficiency, output, price, warranty length, and the availability of readily replaceable parts.
Despite its budget-friendly price tag, the Evolve delivers a strong performance. It achieves efficiency levels of 94% and offers an average kW output of over 40kW. Its compact design and next-day availability make it a practical choice for busy households seeking a quick upgrade.
While several models in the Evolve range scored highly, this ranking is based solely on the 42kW Combi model – the highest performing version.
Score: 64.4/100
The ATAG IR40, known for being a powerful yet compact boiler model, cements its ranking as the third-best boiler.
With a market-leading 14-year warranty, it tops the list for the longest warranty, ensuring peace of mind for buyers. Not only does it offer some security, but it also boasts a powerful output of 38.8kW. Backed by strong efficiency (94%), it could be a solid choice for homes with high heating demands.
Despite scoring high across output, efficiency, warranty, and price, it lacked readily available parts, with only 24% of their stock being available for next-day replacement.
Score: 64.1/100
The Unica MAX 30S from Vokera ranks as the top-performing system boilers in the index, offering excellent value and impressive warranty coverage.
It delivers a high efficiency of 94% and a solid 31.2kW output, making it suitable for medium to large homes with high heating and hot water demand. A standout feature is the generous 10-year warranty, providing long-term peace of mind without additional cost. It also benefits from strong next-day parts availability at 58%, which helps with long-term maintenance and repair.
The Vokera Evolve topped the list of best models, making it not only the best combi boiler in our study, but the best overall boiler model.
The exact model leading the race was the Vokera Evolve C 42kW Combi Gas Boiler, offering a substantial power output for larger homes, a 94% efficiency rating, and an aesthetically pleasing, compact unit. It’s followed by another Vokera model, the Unica Max 35C, as well as boilers from Alpha E-Tec, Ferroli BLUEHELIX RRT, and Viessmann Vitodens.
Here are the top five ranking combi models*:
| Rank | Model | Boiler company | Average output (kW) | Average efficiency (%) | Average warranty length (years) | Average price (£) | Next day availability for parts (%) | Score out of 100 (weighted) |
| 1 | Vokera Evolve C 42kW Combi Gas Boiler | Vokera | 42.0 | 94% | 10 | £1,010 | 58.0% | 65.6 |
| 2 | Vokera Unica Max 35C Combi Gas Boiler | Vokera | 34.4 | 94% | 10 | £905 | 58.0% | 64.9 |
| 3 | Alpha E-TEC PLUS 33kW Combi Gas Boiler | Alpha | 29.7 | 93% | 13 | £925 | 30.3% | 63.8 |
| 4 | Ferroli BLUEHELIX RRT Tech 34C Combi Gas Boiler | Ferroli | 34.0 | 94% | 10 | £875 | 84.3% | 63.5 |
| 5 | Viessmann Vitodens 100-W B1KF 32 kW Combi Gas Boiler | Viessman | 32.0 | 94% | 12 | £1,175 | 37.5% | 63.4 |
* Data note: Only lists one model from each range to avoid repetition and skewed results. Showing you a variety of the best models.
The right boiler size helps you heat your home efficiently without wasting energy or overloading the system. We’ve grouped the best combi boilers by size to help you find the ideal match for your property, whether you’re in a compact flat or a large family home, based on efficiency, warranty, price, and parts availability.
Our leading small combi boilers (24-26 kW) are best suited for flats or homes with 1-2 bedrooms, typically featuring 10 radiators and a single bathroom. Choosing the correct boiler size helps avoid energy waste, as oversized boilers cycle on and off more frequently, resulting in reduced efficiency and increased wear over time.
Here are the best small combi boilers* (24-26kW)
| Rank | Model | Boiler company | Average output (kW) | Average efficiency (%) | Average warranty length (years) | Average price (£) | Next day availability for parts (%) | Score out of 100 (weighted) |
| 1 | Vokera Evolve C 24kW Combi Gas Boiler | Vokera | 24 | 94 | 10 | 845 | 58.0 | 63.4 |
| 2 | Ferroli BLUEHELIX RRT Tech 24C Combi Gas Boiler | Ferroli | 24 | 94 | 10 | 725 | 49.5 | 62.7 |
| 3 | ATAG I24C 24 kW Combi Gas Boiler | ATAG | 24 | 94 | 14 | 1,399 | 24.0 | 62.4 |
| 4 | Viessmann Vitodens 100-W 26 kW Combi Gas Boiler | Viessmann | 26 | 94 | 12 | 1,292 | 37.5 | 62.2 |
| 5 | Vaillant ecoFIT pure 825 Combi Gas Boiler | Vaillant | 25 | 94 | 10 | 907 | 52 | 62 |
* Data note: Only lists one model from each range to avoid repetition and skewed results. Showing you a variety of the best models.
Medium combi boilers (29–31kW) are well-suited for medium-sized homes with 3-4 bedrooms and more than one bathroom, offering a balance of power and energy efficiency without over-specifying for the household’s needs.
Here are the best medium combi boilers* (29-31kW)
| Rank | Model | Boiler company | Average output (kW) | Average efficiency (%) | Average warranty length (years) | Average price (£) | Next day availability for parts (%) | Score out of 100 (weighted) |
| 1 | Worcester Bosch Greenstar 8000 Life 30kW Combi Gas Boiler | Worcester Bosch | 30.0 | 94% | 12 | 1,200 | 29.4% | 61.7 |
| 2 | Vokera Easi-Heat Plus 29Ci Combi Gas Boiler | Vokera | 29.0 | 93% | 5 | 475 | 58.0% | 57.5 |
| 3 | Ariston GENUS ONE NET 30kW Combi Gas Boiler | Ariston | 28.0 | 94% | 12 | 1,825 | 16.1% | 57.4 |
| 4 | Viessmann Vitodens 200-W B2KE 30kW Combi Gas Boiler | Viessmann | 25.4 | 94% | 10 | 1,940 | 37.5% | 57.3 |
| 5 | Vokera Vision 30c Combi Gas Boiler | Vokera | 30.0 | 89% | 6 | 691 | 58.0% | 57.2 |
* Data note: Only lists one model from each range to avoid repetition and skewed results. Showing you a variety of the best models.
Large combi boilers, typically 29 kW and above, are suitable for larger homes with multiple bathrooms, higher water demands, or increased heating needs. These top-ranking models offer a strong combination of warranty, efficiency, and cost, while also considering part availability.
The Vokera Evolve C 42kW ranks highest overall, with the Unica Max 40C just behind. Alpha’s E-TEC PLUS 33kW stands out for its 13-year warranty, while Ferroli offers greater affordability and better access to replacement parts. ATAG places fifth, offering a strong warranty but with a slightly higher price and limited next-day part availability.
Here are the best large combi boilers* (31kW and above):
| Rank | Model | Boiler company | Average output (kW) | Average efficiency (%) | Average warranty length (years) | Average price (£) | Next day availability for parts (%) | Score out of 100 (weighted) |
| 1 | Vokera Evolve C 42kW Combi Gas Boiler | Vokera | 42.0 | 94% | 10 | £1,010 | 58.0% | 65.6 |
| 2 | Vokera Unica Max 40C Combi Gas Boiler | Vokera | 34.4 | 94% | 10 | £1,025 | 58.0% | 64.7 |
| 3 | Alpha E-TEC PLUS 33kW Combi Gas Boiler | Alpha | 33.0 | 93% | 13 | £925 | 30.3% | 64.1 |
| 4 | Ferroli BLUEHELIX RRT Tech 34C Combi Gas Boiler | Ferroli | 34.0 | 94% | 10 | £875 | 49.5% | 63.5 |
| 5 | ATAG I36C 36 kW Combi Gas Boiler | ATAG | 31.2 | 94% | 14 | £1,425 | 24.0% | 63.3 |
* Data note: Only lists one model from each range to avoid repetition and skewed results. Showing you a variety of the best models.
The Vokera Unica MAX 30S System Gas Boiler is the best system boiler, featuring an expansion vessel and eliminating the need for a diverter valve or DHW heat exchanger.
The Unica range ranks highly among other versions, including the combi gas boiler, which ranks second in our overall list. However, it’s the Unica MAX 30 System Boiler that puts it at the top of the list of system boilers.
It’s followed by the Viessmann Vitodens 100-W B1HC 32 kW System Gas Boiler, which ranks sixth in the overall best boiler category. Here’s a look specifically at the top five system boilers* in our rankings:
| Rank | Model | Boiler company | Average output (kW) | Average efficiency (%) | Average warranty length (years) | Average price (£) | Next day availability for parts (%) | Score out of 100 (weighted) |
| 1 | Vokera Unica MAX 30S System Gas Boiler | Vokera | 31.2 | 94% | 10 | £1,040 | 58% | 64.1 |
| 2 | Viessmann Vitodens 100-W B1HC 32 kW System Gas Boiler | Viessmann | 32.0 | 94% | 12 | £1,175 | 37.5% | 63.8 |
| 3 | Ferroli BLUEHELIX RRT Tech 30S System Gas Boiler | Ferroli | 30.0 | 94% | 10 | £750 | 49.5% | 63.3 |
| 4 | ATAG I24S 24 kW System Gas Boiler | ATAG | 23.2 | 94% | 14 | £1,310 | 24.0% | 62.6 |
| 5 | Vaillant ecoTEC plus 637 System Gas Boiler | Vaillant | 37.6 | 94% | 10 | £1,537 | 52% | 62.5 |
* Data note: Only lists one model from each range to avoid repetition and skewed results. Showing you a variety of the best models.
We have categorised the system boilers by size to help you find the ideal power output to heat your home – look through the options for small, medium and large power output (kW).
If you’re looking for a system boiler to heat up a smaller household, then you’ll want to browse the small boilers starting with the Ferroli BLUEHELIX.
Here are the best small system boilers* (24-26kW):
| Rank | Model | Boiler company | Average output (kW) | Average efficiency (%) | Average warranty length (years) | Average price (£) | Next day availability for parts (%) | Score out of 100 (weighted) |
| 1 | Ferroli BLUEHELIX RRT Tech 24S System Gas Boiler | Ferroli | 24.0 | 94 | 10 | 600 | 49.5 | 62.9 |
| 2 | Viessmann Vitodens 100-W B1HF 25 kW System Gas Boiler | Viessmann | 25.0 | 94 | 12 | 1,100 | 37.5 | 62.7 |
| 3 | ATAG I24S 24 kW System Gas Boiler | ATAG | 23.2 | 94 | 14 | 1,310 | 24.0 | 62.6 |
| 4 | Vokera Unica MAX 20S System Gas Boiler | Vokera | 19.5 | 93 | 10 | 933 | 58 | 62.6 |
| 5 | Ferroli BLUEHELIX RRT Tech 18S System Gas Boiler | Ferroli | 18.0 | 94 | 10 | 565 | 49.5 | 62.3 |
The medium system boilers offer a solid output for medium homes with three to four bedrooms. There’s plenty of choice with Voker Unica Max, Ferroli BLUEHELIX RRT, Vaillant ecoFIT, and more.
Here are the best medium system boilers* (29-31kW)
| Rank | Model | Boiler company | Average output (kW) | Average efficiency (%) | Average warranty length (years) | Average price (£) | Next day availability for parts (%) | Score out of 100 (weighted) |
| 1 | Vokera Unica MAX 30S System Gas Boiler | Vokera | 31.2 | 94 | 10 | 1040 | 58.0 | 64.1 |
| 2 | Ferroli BLUEHELIX RRT Tech 30S System Gas Boiler | Ferroli | 30.0 | 94 | 10 | 750 | 49.5 | 63.3 |
| 3 | Vaillant ecoFIT pure 630 System Gas boiler | Vaillant | 30.5 | 94 | 10 | 1,227 | 52.0 | 62.5 |
| 4 | Worcester Bosch Greenstar 8000 Life 30kW System Gas Boiler | Worcester Bosch | 30.0 | 94 | 10 | 1,211 | 29.4 | 61.6 |
| 5 | Worcester Bosch Greenstar 8000 Style 30kW System Gas Boiler | Worcester Bosch | 30.0 | 94 | 12 | 1,317 | 29.4 | 61.4 |
* Data note: Only lists one model from each range to avoid repetition and skewed results. Showing you a variety of the best models.
The larger system boilers offer up to 121kW of output for big buildings and commercial properties. This list also includes the Vokera Unica max once again and the inclusion of the Worcester Bosch Greenstar line.
Here are the best large system boilers* (31kW and above):
| Rank | Model | Boiler company | Average output (kW) | Average efficiency (%) | Average warranty length (years) | Average price (£) | Next day availability for parts (%) | Score out of 100 (weighted) |
| 1 | Vokera Unica MAX 30S System Gas Boiler | Vokera | 31.2 | 94 | 10 | 1,040 | 58.0 | 64.1 |
| 2 | Viessmann Vitodens 100-W B1HC 32 kW System Gas Boiler | Viessmann | 32.0 | 94 | 12 | 1,175 | 37.5 | 63.4 |
| 3 | Vaillant ecoTEC plus 637 System Gas Boiler | Vaillant | 37.6 | 94 | 10 | 1,537 | 52.0 | 62.5 |
| 4 | Alpha ProTec Plus 115 System Gas Boiler | Alpha | 121.0 | 92 | 5 | 1,246 | 52.8 | 62.0 |
| 5 | Worcester Bosch Greenstar 8000 Life 35kW System Gas Boiler | Worcester Bosch | 35.0 | 92 | 12 | 1,357 | 29.4 | 61.9 |
* Data note: Only lists one model from each range to avoid repetition and skewed results. Showing you a variety of the best models.
ATAG IR40 40kW Regular Gas Boiler is the best conventional boiler, ranking above over 800 other models in our study.
Conventional boilers (heat-only) such as the ATAG IR40 are renowned for providing a consistent high-capacity water supply, making them ideal for larger homes with multiple bathrooms.
Let’s take a look at the top-ranking conventional boiler models*:
| Rank | Model | Boiler company | Average output (kW) | Average efficiency (%) | Average warranty length (years) | Average price (£) | Next day availability for parts (%) | Score out of 100 (weighted) |
| 1 | ATAG IR40 40kW Regular Gas Boiler | ATAG | 38.8 | 94% | 14 | £1,390 | 19.5 | 64.4 |
| 2 | Vaillant ecoFIT Pure 430 Regular Gas Boiler | Vaillant | 30.5 | 94% | 10 | £1,002 | 68.3 | 63.1 |
| 3 | Worcester Bosch Greenstar 8000 Life 30kW Regular Gas Boiler | Worcester Bosch | 30.0 | 94% | 12 | £1,255 | 36.5 | 61.5 |
| 4 | Baxi 830 Heat 30kW Regular Gas Boiler | Baxi | 30.0 | 93% | 10 | £944 | 75.6 | 59.9 |
| 5 | Worcester Bosch Greenstar 24Ri Regular Gas Boiler | Worcester Bosch | 24.0 | 92% | 10 | 954 | 29.4 | 58.0 |
* Data note: Only lists one model from each range to avoid repetition and skewed results. Showing you a variety of the best models.
We have categorised the heat-only (conventional) boilers by size to help you filter through the ideal boiler for your home size – check out the best small, medium, and large regular boilers below.
Here are the best small heat-only (regular) boilers, ranging from 24 to 26 kW, suitable for smaller homes with modest heating needs and a separate hot water cylinder system.
These models strike a balance between strong efficiency scores and long warranties, with ATAG leading the category thanks to its standout 14-year warranty. Vaillant also ranks highly, boosted by its part availability, while Ideal trails slightly due to lower next-day availability.
Here are the best small heat-only boilers* (24-26kW):
| Rank | Model | Boiler company | Average output (kW) | Average efficiency (%) | Average warranty length (years) | Average price (£) | Next day availability for parts (%) | Score out of 100 (weighted) |
| 1 | ATAG IR24 24kW Regular Gas Boiler | ATAG | 23.2 | 94 | 14 | 1,270 | 24.0 | 62.8 |
| 2 | Vaillant ecoFIT Pure 425 Regular Gas Boiler | Vaillant | 25.4 | 94 | 10 | 976 | 52.0 | 62.5 |
| 3 | Baxi 825 Heat 25kW Regular Gas Boiler | Baxi | 25.0 | 93 | 10 | 885 | 34.5 | 59.5 |
| 4 | Worcester Bosch Greenstar 24Ri Regular Gas Boiler | Worcester Bosch | 24.0 | 92 | 10 | 954 | 29.4 | 58.0 |
| 5 | Ideal Logic Max Heat H24 Regular Gas Boiler | Ideal | 24.2 | 94 | 10 | 998 | 14.7 | 56.0 |
* Data note: Only lists one model from each range to avoid repetition and skewed results. Showing you a variety of the best models.
Here are the best medium-sized heat-only (regular) boilers, suited for 3-4 bedroom homes with moderate heating and hot water needs. These boilers offer a solid balance of power and efficiency while giving flexibility with separate hot water cylinders.
Vaillant’s ecoFIT Pure 430 tops the list with the highest overall score, supported by excellent efficiency and part availability. Worcester Bosch offers a longer warranty of 12 years, while Baxi and Potterton stand out for affordability, with models available for under £1,000.
Here are the best medium heat-only boilers* (29-31kW)
| Rank | Model | Boiler company | Average output (kW) | Average efficiency (%) | Average warranty length (years) | Average price (£) | Next day availability for parts (%) | Score out of 100 (weighted) |
| 1 | Vaillant ecoFIT Pure 430 Regular Gas Boiler | Vaillant | 30.5 | 94 | 10 | 1,002 | 52.0 | 63.1 |
| 2 | Worcester Bosch Greenstar 8000 Life 30kW Regular Gas Boiler | Worcester Bosch | 30.0 | 94 | 12 | 1,255 | 29.4 | 61.5 |
| 3 | Baxi 830 Heat 30kW Regular Gas Boiler | Baxi | 30.0 | 93 | 10 | 944 | 34.5 | 60.0 |
| 4 | Ideal Logic Max Heat H30 Regular Gas Boiler | Ideal | 30.3 | 93 | 10 | 1,117 | 14.7 | 56.0 |
| 5 | Potterton Titanium 30kW Regular Gas Boiler | Potterton | 30.0 | 93 | 7 | 840 | 34.0 | 55.6 |
* Data note: Only lists one model from each range to avoid repetition and skewed results. Showing you a variety of the best models.
These large heat-only boilers, typically above 31kW, are ideal for large properties with high heating and hot water demands, often featuring multiple bathrooms or older heating systems with traditional radiators.
The ATAG IR40 leads this group with a strong warranty and solid balance of efficiency and price, while Vaillant’s Pure 435 scores highly for part availability.
Here are the best large heat-only boilers* (31kW and above):
| Rank | Model | Boiler company | Average output (kW) | Average efficiency (%) | Average warranty length (years) | Average price (£) | Next day availability for parts (%) | Score out of 100 (weighted) |
| 1 | ATAG IR40 40kW Regular Gas Boiler | ATAG | 38.8 | 94 | 14 | 1,390 | 24.0 | 64.4 |
| 2 | Vaillant ecoFIT Pure 435 Regular Gas Boiler | Vaillant | 34.8 | 94 | 10 | 1,533 | 52.0 | 62.1 |
| 3 | Worcester Bosch Greenstar 8000 Life 50kW Regular Gas Boiler | Worcester Bosch | 50.0 | 94 | 12 | 2,300 | 29.4 | 61.1 |
| 4 | Vaillant ecoTEC plus 435 Regular Gas Boiler | Vaillant | 35.1 | 93 | 10 | 1,453 | 52.0 | 54.5 |
| 5 | Worcester Bosch Greenstar FS 42CDi Regular Gas Boiler | Worcester Bosch | 41.0 | 92 | 7 | 2,091 | 29.4 | 52.3 |
* Data note: Only lists one model from each range to avoid repetition and skewed results. Showing you a variety of the best models.
Alpha ranks as the best boiler brand overall, with a weighted score of 65.5 out of 100. In addition to placing two models in the top 20 (the E-TEC Plus 33kW and the ProTec Plus 115), Alpha’s consistent performance across output, efficiency, warranty, and price helped it top the list of boiler companies.
While Alpha didn’t score as highly as some competitors for stocked parts availability, its all-round performance still beat Vokera (64.8), Vaillant (60.5), Ferroli (60.0), and ATAG (57.6). These scores reflect the strength of each brand’s full boiler range, not just individual standout models.
Vokera ranked second overall with a weighted score of 64.8, scoring highly due to its excellent next-day availability rate (58%) and affordable pricing (£742 average), making it a strong option for those on a budget.
| Rank | company | Average Kw | Average efficiency (%) | Average warranty | Average price | Next-day parts availability (%) | Score out of 100 (weighted) |
| 1 | Alpha | 41 | 93 | 8 | £954 | 30.3% | 65.5 |
| 2 | Vokera | 28 | 93 | 7 | £742 | 58.0% | 64.8 |
| 3 | Vaillant | 26 | 94 | 9 | £1,263 | 52.0% | 60.5 |
| 4 | Ferroli | 19 | 96 | 7 | £714 | 49.5% | 60.0 |
| 5 | ATAG | 26 | 94 | 14 | £1,824 | 24.0% | 57.6 |
| 6 | Baxi | 23 | 93 | 7 | £888 | 34.5% | 57.5 |
| 7 | Johnson & Starley | 22 | 93 | 8 | £805 | 24.3% | 56.9 |
| 8 | Biasi | 24 | 92 | 6 | £618 | 26.7% | 56.8 |
| 9 | Intergas | 26 | 93 | 7 | £946 | 25.9% | 56.5 |
| 10 | Glow-worm | 23 | 91 | 6 | £725 | 19.8% | 54.2 |
| 11 | Keston | 39 | 90 | 7 | £1,651 | 24.0% | 54.1 |
| 12 | Ravenheat | 25 | 91 | 4 | £768 | 35.6% | 54.0 |
| 13 | Ariston | 26 | 93 | 8 | £1,168 | 16.1% | 53.2 |
| 14 | Ideal | 23 | 93 | 9 | £1,177 | 14.7% | 52.4 |
| 15 | Navien | 28 | 93 | 9 | £1,350 | 0% | 52.0 |
| 16 | Worcester Bosch | 30 | 92 | 7 | £1,650 | 29.4% | 51.8 |
| 17 | Main | 22 | 93 | 5 | £654 | 6.9% | 51.1 |
| 18 | Potterton | 23 | 91 | 3 | £974 | 34.0% | 48.5 |
| 19 | Heatline | 22 | 89 | 2 | 492 | 14.1% | 48.1 |
| 20 | Zanussi | 23 | 93 | 3 | £668 | 9.1% | 47.9 |
| 21 | Viessmann | 25 | 95 | 7 | £2,256 | 37.5% | 44.7 |
Vaillant, Ferroli, and ATAG complete the top five. Ferroli stood out for efficiency and warranty length, while ATAG’s score was driven almost entirely by its industry-leading 14-year average warranty, despite higher prices and limited stock availability.
Other well-known names like Worcester Bosch, Ideal, and Viessmann appear lower in the rankings, this is largely due to high average prices and limited replacement stock availability in the UK. Brands such as Heatline and Zanussi offer budget-friendly options but fall short on performance and reliability metrics.
ATAG almost tripled the average warranty length (five years) with their average warranty of 14 years across their models. Although let down by their lack of readily available parts in the UK (24% next-day availability) they still boast the best warranty length by far, outgunning Vaillant, Ideal, and Navien, who all offer an average of nine years warranty.
We found models such as the ATAG I24, I28, I32 and more come with an average warranty of 14 years. All of their boilers come with at least 12 years warranty and can be extended to 18 years.[3]
Warranties are important for peace of mind, but it’s interesting to see that there’s no direct correlation between price and the length of a company’s warranty.
The boiler brand with the longest average warranty (ATAG) has an average price of 1,824.
The scatter plot highlights the insignificance of price to warranty and how there’s no direct relationship between the two, with the longest and shortest warranty both costing between £1,500 – £1,900.
Our study found that the average cost of a boiler is £1,090, but the cost of a boiler varies from one brand to the next. Other factors such as build quality, size, and features may also affect the price.
Heatline offers the most affordable boilers with an average price of £492. They’re followed by Biasi (£618) and Vokera (£742).
Our study found that the average cost of boiler parts across all brands is £286.75, with major components such as the heat exchanger pushing the average up. The heat exchanger is the most expensive part at £1,249, followed by the fans at £242.20 and the gas valve at £232.70.
When purchasing a boiler, parts are important to consider, in case you are required to replace a part in future. Fixes for a boiler can become costly, and that’s why checking that your boiler has warranty, readily accessible parts, and affordable replacements is important.
If you’re having issues with your boiler, it could be worth exploring repairs before considering a new model. Our qualified engineers offer boiler repair services to help get things running again – with emergency boiler, gas boiler, central heating repairs, and even routine maintenance.
Of the top five boiler brands in our rankings, only Vaillant had an average part cost above the UK brand average in our study (£245), with an average of £286.75 across the main components. Alpha (£148), Vokera (£188), Ferroli (£201), and ATAG (£155) all came in under average.
The data shows a wide gap in part price between brands, with Alpha offering the most affordable replacements on average (out of the top five brands).
This stark contrast underlines how drastically costs can vary by brand, making it crucial for buyers to factor in parts replacement prices, not just boiler efficiency or warranty lengths. Heat exchangers are the most expensive boiler part on average, costing £1249 across all brands. The highest price was from Elco at £3,521, while the lowest was from Biasi, whose heat exchanger and DHW heat exchangers averaged just £107 across their different types of boilers, more than 30 times cheaper (£3,414 lower). This wide disparity reinforces the importance of checking the cost of key parts.
Boiler efficiency varies across different fuel types, impacting long-term energy costs and performance. Combi (system) and gas boilers offer the highest average efficiency at 92.7% (A rating) and 92.5% (A rating), while oil boilers follow closely at 91%.
Electric boilers, despite having some of the most efficient individual models, have the average efficiency of 90% (B rating).
Vokera scored highest for parts availability, catapulting the company and its models into the top rankings list, with 58% of its models supported by next-day replacement access.
Among non-electric brands, Ferroli leads with models averaging 94% efficiency across their models.
In February 2025, we analysed 888 boiler models across 31 UK boiler brands using data from trusted third-party sources including Boiler Guide and DHS Spares.
We scored each model using a weighted scoring system, factoring in:
Additional boiler model information was cross-verified with BOXT, Green Central, Heatable, and Compare Companies to ensure data accuracy. Replacement part costs and availability were sourced primarily from DHS Spares and City Plumbing, with availability indicating UK next-day delivery status where applicable.
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