Let’s be honest - shopping for a new boiler isn’t anyone’s idea of a good time. But if you’re going to spend a few grand on something that powers your heating and hot water, you want to get it right.
With dozens of brands and models out there, finding the best boiler in the UK can feel like wading through sludge. Luckily, we’ve done the hard graft for you.
Based on real sales data, industry awards, and thousands of customer reviews, we’ve nailed down the #1 boiler in the UK for 2025 - and yep, it’s a name you’ll definitely recognise.
P.S. We install a wide range of boilers nationwide with Gas Safe engineers. Just answer a few quick questions to get your fixed price — and you could have your new boiler fitted as soon as tomorrow.
First off: how do we define “#1”?
Before we crown the champion, let’s break down what makes a boiler stand out. At Heatable, we evaluate boilers based on:
Sales Figures - high sales reflect consumer trust and market dominance.
Industry Awards - awards and endorsements from trusted names like Which? signals quality and performance.
Customer Reviews - real-world feedback from homeowners and engineers tells us about reliability and aftercare.
Efficiency and Features - saving cash and cutting carbon? Yes, please.
Aftercare – how solid is the warranty, and how easy is it to get help if something goes wrong?
Using these criteria, one boiler rises above the rest: the Worcester Bosch Greenstar 4000.
Why the Worcester Bosch Greenstar 4000 Is #1
Leading the Pack in Sales
Worcester Bosch is a household name in the UK, and for good reason. The brand dominates the market, with the Clean Heat Market Mechanism (CHMM) reporting that the top four manufacturers, including Worcester Bosch, sell around 1.5 million gas boilers annually in the UK.
While exact model-specific sales are trickier to pin down, the Greenstar range - especially the 4000 model - is a flagship product, widely installed by Gas Safe engineers across the country. Its popularity stems from its versatility, fitting small flats to larger homes with ease.
Award-Winning Performance
The Worcester Bosch Greenstar 4000 has bagged some serious silverware. It’s been awarded the Which? Best Buy Award for 14 consecutive years, a testament to its reliability and customer satisfaction.
In Which?’s 2024 survey of 10,028 homeowners and 198 heating engineers, Worcester Bosch scored an impressive 82% overall, with the Greenstar 4000 praised for its ease of repair and stellar customer service.
This model also boasts a 94% efficiency rating, making it one of the most eco-friendly gas boilers on the market.
Rave Reviews from Homeowners and Engineers
When it comes to reviews, the Greenstar 4000 shines. On Trustpilot, Worcester Bosch enjoys a 4.7/5 rating from over 40,000 reviews, with customers praising the 4000’s quiet operation, energy savings, and robust build. Engineers love it too, citing easy access to spare parts and straightforward servicing.
In Which?’s surveys, Worcester Bosch consistently earns high marks for reliability, with fewer breakdowns reported compared to competitors. One customer summed it up perfectly: “It’s a boiler you fit and forget - reliable and efficient.”
Prefer video? Our co-founder Ben Price joins Gas Engineer Allen Hart to put the Worcester Bosch 4000 through its paces - watch below.
Standout Features
The Greenstar 4000 isn’t just popular; it’s packed with features that make it a homeowner’s dream:
High Efficiency: A 94% ErP rating means lower energy bills and a reduced carbon footprint.
Smart Compatibility: Works with Bosch EasyControl and other smart thermostats for remote heating management.
Quick Tap Technology: A flick of the tap pre-heats water, delivering instant hot water and minimising waste.
Long Warranty: Up to 10 years (or 12 with a Worcester-accredited installer), giving you peace of mind.
Available as a combi or system boiler in various outputs (25 kw to 42 kw), it’s adaptable to homes of all sizes. Plus, it’s hydrogen-blend ready, future-proofing your investment as the UK transitions to greener fuels.
“Worcester Bosch is the UK’s go-to boiler brand for a reason. As an engineer, the big win is how easy and affordable parts are to get — quicker fixes, lower costs, less hassle.” - Patrick Garner, Gas Safe Engineer.
How Does It Stack Up Against the Competition?
While the Greenstar 4000 takes the top spot, other boilers like the Viessmann Vitodens 100-W and Vaillant ecoTEC Plus are strong contenders.
The Viessmann boasts a 98% efficiency rating and cutting-edge tech like the Inox-Radial heat exchanger, but it’s pricier and less widely installed.
Vaillant’s ecoTEC Plus is a favourite for its quiet operation and 10-year warranty, but it lags slightly in Which? scores compared to Worcester Bosch.
What sets the Greenstar 4000 apart is its balance of affordability, reliability, and widespread engineer support. It’s not the cheapest - expect to pay £1,500–£2,500 (excluding installation) - but its long-term value and low running costs make it a worthy investment.
Comparing the UK’s Top Boiler Brands in 2025
The table below compares Worcester Bosch, Vaillant, Viessmann, Baxi, and Ideal based on sales, awards, warranty, Trustpilot reviews, and aftercare. Sourced from Which?, Trustpilot, and industry reports, it highlights why Worcester Bosch leads as the UK’s #1 boiler brand.
Criteria | Worcester Bosch | Vaillant | Viessmann | Baxi | Ideal |
Sales | Market leader (~1.5M boilers sold annually, CHMM). Greenstar 4000 widely installed. | Strong premium market share, slightly behind Worcester Bosch. | Growing but less dominant than top brands. Popular in trade. | Solid mid-range sales (~25% market share). | High sales in budget/mid-range, trails Worcester Bosch. |
Awards | Which? Best Buy 14 years (2011–2024), Royal Warrant. | Which? Best Buy 2020, 80% survey score. | Trade-focused accolades, fewer consumer awards. | Good Housekeeping awards, less frequent Which? wins. | Queen’s Award (2013, 2019), Good Housekeeping (2013, 2017). |
Warranty | 5–7 years, up to 10–12 years (guarantee) with accredited installer. | 5 years, 7–10 years with Advance installer (warranty). | 7 years, up to 10–12 years with accredited installer. | 7 years standard (warranty). | 7–10 years, up to 12 years with Max-accredited installer. |
Trustpilot | 4.6/5 (47,135 reviews, 2025). 79% 5-star. Reliable, quiet. | 4.4/5 (20,000+ reviews). Quality praised, slightly lower score. | 4.0/5 (~10,000 reviews). Mixed, some installer issues. | 4.5/5 (25,000+ reviews). Good for budget models. | 4.8/5 (43,000 reviews, 2025). High satisfaction, affordable. |
Aftercare | 24/7 support, live chat, fast engineer service. 96% positive feedback. | Reliable, 5/5 Which? for spares. No live chat, call charges apply. | Good parts availability, smaller engineer network. | Strong UK parts, 7/7 support. Slightly less praised. | 7/7 support, live chat. Excellent but smaller network than Worcester. |
Why Trust Heatable’s Verdict?
At Heatable, we’re not just about selling boilers; we’re about finding the right fit for your home.
Our Gas Safe engineers have installed thousands of Worcester Bosch boilers, and we’ve seen firsthand how the Greenstar 4000 performs.
We cross-reference industry data, customer feedback, and expert opinions to ensure our recommendations are rock-solid. Sources like Which?, Trustpilot, and Boiler Guide back up our choice, giving you confidence in our pick.
Ready to Upgrade Your Boiler?
The Worcester Bosch Greenstar 4000 is the #1 boiler in the UK for 2025, blending top sales, award-winning performance, and glowing reviews.
Whether you’re replacing an old boiler or installing a new one, this model delivers warmth, efficiency, and reliability without breaking the bank.
Want to see how it fits your home? Get a fixed-price quote from Heatable in under a minute.
Our hassle-free online system connects you with trusted installers, and with 0% APR finance options, you can spread the cost affordably. Click here to start your journey to a warmer, more efficient home!
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 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.
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To learn more about boilers, visit our advice section, check out our YouTube channel, or read customer testimonials here.
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