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The best boiler is the one that suits your home and is fitted well. These are the brands we install most, why we fit them, what a fitted boiler costs and how long the warranties last. Below that are the full results of our study of 888 boiler models.
| Brand | Why we fit it | Manufacturer warranty |
|---|---|---|
| Worcester Bosch | We’re an accredited installer, and parts are easy to get in London, so repairs are quick. | Up to 12 years, depending on model |
| Vaillant | We’re an accredited installer, and the ecoTEC range is compact and quiet, which suits flats. | 5 to 10 years, depending on model |
| Ideal | The Logic range is good value and parts are widely stocked. | 5 to 10 years, depending on model |
| Baxi | Straightforward to service and sensibly priced. | 5 to 10 years, depending on model |
Every installation also comes with our own guarantee of at least 12 months.
| Boiler type | Typical fitted price |
|---|---|
| Combi boiler (replacing an existing combi) | from £1,795 + VAT |
| Larger combi boiler | from £2,455 + VAT |
| System boiler | from £1,958 + VAT |
| Conventional (regular) boiler | from £1,925 + VAT |
All prices are + VAT and are “from” prices for parts and labour, fitted. They vary depending on the boiler make and model and job complexity, and we confirm a fixed price before work starts. Prices apply during office hours; parking or the congestion charge may be added.
Not sure which type you need? See which heating system suits your home.
Get a free boiler quote: 0203 504 4000
Or request a quote online on our boiler installation page.
We scored 888 boiler models from 21 brands to find the best boilers in the UK. Each model was scored on power output, efficiency, warranty length, average price and how many of its spare parts were in stock for next-day delivery. Prices in the study are for the boiler only, not fitted.
Warranties were correct when the study was written. They can change, and may need registration or an accredited installer.
| Category | Top model | Output | Efficiency | Warranty | Boiler price | Score |
|---|---|---|---|---|---|---|
| Best combi | Vokera Evolve C 42kW | 42.0kW | 94% | 10 years | £1,010 | 65.6 |
| Best regular (heat-only) | ATAG IR40 40kW | 38.8kW | 94% | 14 years | £1,390 | 64.4 |
| Best system | Vokera Unica MAX 30S | 31.2kW | 94% | 10 years | £1,040 | 64.1 |
The Vokera Evolve C 42kW scored best overall, with 94% efficiency, a 10-year warranty and 58% of its parts in stock for next-day delivery. The ATAG IR40 has the longest warranty of the three at 14 years, but only 24% of its parts were available next day. The Vokera Unica MAX 30S suits medium to large homes with a higher demand for heating and hot water.
The top five combi models, showing one model from each range:
| Rank | Model | Output | Efficiency | Warranty | Boiler price | Parts next day | Score |
|---|---|---|---|---|---|---|---|
| 1 | Vokera Evolve C 42kW | 42.0kW | 94% | 10 years | £1,010 | 58.0% | 65.6 |
| 2 | Vokera Unica Max 35C | 34.4kW | 94% | 10 years | £905 | 58.0% | 64.9 |
| 3 | Alpha E-TEC PLUS 33kW | 29.7kW | 93% | 13 years | £925 | 30.3% | 63.8 |
| 4 | Ferroli BLUEHELIX RRT Tech 34C | 34.0kW | 94% | 10 years | £875 | 49.5% | 63.5 |
| 5 | Viessmann Vitodens 100-W B1KF 32kW | 32.0kW | 94% | 12 years | £1,175 | 37.5% | 63.4 |
A system boiler works with a separate hot water cylinder, so it suits homes with more than one bathroom. The top five:
| Rank | Model | Output | Efficiency | Warranty | Boiler price | Parts next day | Score |
|---|---|---|---|---|---|---|---|
| 1 | Vokera Unica MAX 30S | 31.2kW | 94% | 10 years | £1,040 | 58.0% | 64.1 |
| 2 | Viessmann Vitodens 100-W B1HC 32kW | 32.0kW | 94% | 12 years | £1,175 | 37.5% | 63.8 |
| 3 | Ferroli BLUEHELIX RRT Tech 30S | 30.0kW | 94% | 10 years | £750 | 49.5% | 63.3 |
| 4 | ATAG I24S 24kW | 23.2kW | 94% | 14 years | £1,310 | 24.0% | 62.6 |
| 5 | Vaillant ecoTEC plus 637 | 37.6kW | 94% | 10 years | £1,537 | 52.0% | 62.5 |
Conventional boilers work with a hot water cylinder and cold water tanks, and suit larger homes on an older system. The top five:
| Rank | Model | Output | Efficiency | Warranty | Boiler price | Parts next day | Score |
|---|---|---|---|---|---|---|---|
| 1 | ATAG IR40 40kW | 38.8kW | 94% | 14 years | £1,390 | 24.0% | 64.4 |
| 2 | Vaillant ecoFIT Pure 430 | 30.5kW | 94% | 10 years | £1,002 | 52.0% | 63.1 |
| 3 | Worcester Bosch Greenstar 8000 Life 30kW | 30.0kW | 94% | 12 years | £1,255 | 29.4% | 61.5 |
| 4 | Baxi 830 Heat 30kW | 30.0kW | 93% | 10 years | £944 | 34.5% | 60.0 |
| 5 | Worcester Bosch Greenstar 24Ri | 24.0kW | 92% | 10 years | £954 | 29.4% | 58.0 |
These scores cover each brand’s whole range, not just its best model. Alpha came top with 65.5 out of 100, thanks to consistent output, efficiency, warranty and price. Vokera was second (64.8), helped by the best next-day parts availability (58%) and a low average price (£742).
| Rank | Brand | Efficiency | Warranty | Boiler price | Parts next day | Score |
|---|---|---|---|---|---|---|
| 1 | Alpha | 93% | 8 years | £954 | 30.3% | 65.5 |
| 2 | Vokera | 93% | 7 years | £742 | 58.0% | 64.8 |
| 3 | Vaillant | 94% | 9 years | £1,263 | 52.0% | 60.5 |
| 4 | Ferroli | 96% | 7 years | £714 | 49.5% | 60.0 |
| 5 | ATAG | 94% | 14 years | £1,824 | 24.0% | 57.6 |
| 6 | Baxi | 93% | 7 years | £888 | 34.5% | 57.5 |
| 10 | Glow-worm | 91% | 6 years | £725 | 19.8% | 54.2 |
| 14 | Ideal | 93% | 9 years | £1,177 | 14.7% | 52.4 |
| 16 | Worcester Bosch | 92% | 7 years | £1,650 | 29.4% | 51.8 |
| 18 | Potterton | 91% | 3 years | £974 | 34.0% | 48.5 |
Worcester Bosch and Ideal rank lower in the study mainly because of higher average prices and fewer parts in stock for next-day delivery. That does not make them poor boilers. Worcester Bosch and Vaillant are the brands we fit most, because we are accredited installers and can get their parts quickly in London.
ATAG’s average warranty of 14 years is almost three times the five-year average across all brands, and every ATAG boiler comes with at least 12 years. Vaillant, Ideal and Navien follow with an average of nine years. We found no link between price and warranty length: the brands with the longest and shortest warranties both average £1,500 to £1,900.
The average boiler in the study cost £1,090, boiler only. Heatline was the cheapest brand on average at £492, followed by Biasi (£618) and Vokera (£742).
Replacement parts averaged £286.75 across all brands. The heat exchanger was the most expensive part at £1,249 on average, followed by the fan (£242.20) and the gas valve (£232.70). Heat exchanger prices varied hugely, from £107 for Biasi to £3,521 for Elco, so it is worth checking part prices and availability as well as the price of the boiler.
Gas combi and system boilers averaged 92.7% efficiency and gas boilers overall 92.5%, both A rated. Oil boilers followed at 91%. Electric boilers averaged 90% (B rated), although some individual electric models scored higher.
In February 2025 we analysed 888 boiler models across 21 UK boiler brands, using data from Boiler Guide and DHS Spares. Each model was given a weighted score for efficiency, power output, warranty length, average price and next-day parts availability.
Model details were cross-checked against BOXT, Green Central, Heatable and Compare Companies. Replacement part prices and availability came mainly from DHS Spares and City Plumbing, with availability based on UK next-day delivery. Each table shows one model from each range, so a single range does not fill the list. Warranty details come from the manufacturers, for example ATAG’s warranty page.
In our study, Vokera, with 58% of its parts in stock for next-day delivery. That helped its models rank highly.
Ferroli’s range averaged 96% across its models, the highest of any brand. Most modern gas boilers are 92 to 94% efficient.
Not always, but a longer warranty and good parts availability usually mean fewer and quicker repairs. Correct sizing and a good installation matter as much as the brand.
See our combi sizing guide.