Best Combi Boilers in the UK: Compare Popular Models Before You Buy

How Much Does a New Combi Boiler Cost?

Combi boiler prices in the UK typically range from around £800 for a budget entry-level unit up to £2,000+ for a premium, high-output model. Installation adds to that, and the total depends on whether it's a straight combi-to-combi swap or a full conversion from a system or regular boiler with a tank in the loft.

As a rough guide:

• Budget combi boilers (Baxi Main, Vaillant ecoFIT Pure entry models, Ideal Logic): £800–£1,300
• Mid-range combi boilers (Baxi 800 series, Worcester Bosch Greenstar 4000, Ideal Vogue Max): £1,100–£1,700
• Premium combi boilers (Vaillant ecoTEC Plus, Worcester Greenstar 8000 Life, Viessmann): £1,600–£2,500+

These are unit prices only. Installation cost sits on top and varies by property — flue routing, pipework, and whether you're relocating the boiler all affect the final figure. The only way to get an accurate number for your home is a property-specific quote.

What Size Combi Boiler Do I Need?

Combi boiler output is measured in kW, and the right size depends on how many bathrooms you're running and how big your home is — not the boiler's price tag. Output affects how well a boiler copes with hot water demand: an undersized unit can struggle to keep up when more than one outlet is running at once, though the flow and pressure you actually feel at the tap also depend on your mains supply and pipework, not output alone.

• 1 bathroom, up to 2 bedrooms: a 24–28kW combi is usually enough
• 1 bathroom, 3 bedrooms: look at 28–32kW, which gives more headroom when the shower and kitchen tap are both in use
• 2 bathrooms, 3–4 bedrooms: step up to 32–36kW, which is where models like the Baxi 836, Vaillant ecoFIT Pure 835 and Ideal Vogue Max 32 sit
• 2+ bathrooms, larger homes: 35kW and above, such as the Worcester Greenstar 8000 Life or Ideal Vogue Max 40kW

If you're not sure which bracket your home falls into, our engineers can assess your property — pipework, insulation, mains pressure and hot water demand — and confirm the right output as part of a proper survey.

Baxi Combi Boilers

Baxi boilers carry a SEDBUK A-rating across the range and are built to be compact enough for a standard kitchen cupboard. Some current models, including the 836, are hydrogen-ready — check the individual review for confirmation on a specific model, since this isn't consistent across the whole range. Baxi tends to sit at the more affordable end of the market without cutting corners on warranty length.

Baxi 836 Combi Boiler. The most powerful unit in the 800 range, with 26.4kW for central heating and 36kW for hot water. Built for medium-sized homes with up to two bathrooms, it comes with a 10-year manufacturer warranty (register within 30 days of installation). Read the full Baxi 836 combi boiler review for the latest price guidance, output breakdown and FAQ.

Baxi 800 Combi Boiler. An overview of the Baxi 800 series, covering the range's output options and where each one fits. See the Baxi 800 combi boiler review for sizing guidance.

Baxi 830 Combi Boiler. Sits between the 800 and the 836 on output. Full detail in the Baxi 830 combi boiler review.

Baxi Main Eco Compact 30kW. A budget-conscious option from Baxi's Main range, with a smaller footprint that suits flats and smaller properties where cupboard space is tight. Read the Baxi Main Eco Compact 30kW review.

Not sure which Baxi fits your property? The Baxi combi boiler reviews roundup compares the models we've reviewed side by side.

Worcester Bosch Combi Boilers

Worcester Bosch is one of the most recognised names in UK heating, and the Greenstar range covers everything from compact flats to larger family homes. Build quality and parts availability are among the reasons engineers recommend the brand — servicing and repairs tend to be straightforward, since most Gas Safe engineers, including ours, work on Worcester Bosch units regularly.

Worcester Bosch Greenstar 4000. A reliable mid-range combi built for typical two-to-three-bedroom homes, with the compact casing Worcester Bosch is known for. Details in the Worcester Bosch Greenstar 4000 boiler review.

Worcester Bosch Greenstar 4000 30kW. The 30kW output variant of the 4000 range, sized for homes with slightly higher heating demand. See the Worcester Bosch Greenstar 4000 30kW review.

Worcester Greenstar 8000 Life 35kW. One of Worcester Bosch's higher-output models, aimed at homes with higher hot-water demand. Read the Worcester Greenstar 8000 Life 35kW review.

Worcester Greenstar 36Cdi Compact. An older but still widely fitted model, popular for straightforward like-for-like replacements. See the Worcester Greenstar 36Cdi Compact review.

For the full lineup in one place, the Worcester Bosch boiler reviews page covers the Worcester Bosch models we've reviewed.

Ideal Combi Boilers

Ideal Boilers has built its reputation on straightforward, reliable units across a wide output range, with the Logic and Vogue Max families covering most UK households. It's a British-made brand, and tends to sit slightly below Worcester Bosch and Vaillant on price while still offering solid warranty terms — a common choice where budget matters but reliability can't be compromised.

Ideal Logic. Ideal's entry-level combi, a solid, no-frills choice for smaller homes and flats. Read the Ideal Logic boiler review.

Ideal Logic Max C30. A step up in output from the standard Logic, suited to slightly larger homes with one bathroom. See the Ideal Logic Max C30 boiler review.

Ideal Esprit Eco2 30kW. A mid-tier model with a compact case, positioned between Ideal's entry and premium ranges. Full details in the Ideal Esprit Eco2 30kW boiler review.

Ideal Instinct. One of Ideal's more recent boiler ranges, built with a focus on quiet running and simplified servicing. Read the Ideal Instinct boiler review.

Ideal Vogue. Ideal's premium range, sitting above the Logic and Esprit Eco2 on output and build. See the Ideal Vogue boiler review for a full look at the range before checking the specific Vogue Max outputs below.

Ideal Vogue Max 32. A higher-output combi from Ideal's premium Vogue Max range, worth a look if your household has higher hot-water demand than a standard one-bathroom home — check the review for the full output detail. See the Ideal Vogue Max 32 boiler review.

Ideal Vogue Max 40kW. The largest output in the Vogue Max range, built for bigger homes or higher simultaneous hot water demand. Full spec in the Ideal Vogue Max 40kW review.

Ideal Atlantic 30kW. A dependable mid-output option from Ideal, commonly fitted as a direct combi replacement. Read the Ideal Atlantic 30kW boiler review.

Vaillant Combi Boilers

Vaillant's ecoTEC and ecoFIT Pure ranges are among the most widely specified combi boilers in the UK. The German engineering reputation carries a slight price premium over Baxi and Ideal, and it's a brand engineers generally rate well — though as with any brand, reliability comes down to correct sizing and regular servicing as much as the badge on the case.

Vaillant ecoTEC Plus. Vaillant's flagship range, a proven performer across a wide range of home sizes. Read the Vaillant ecoTEC Plus review.

Vaillant ecoTEC Plus 832. The higher-output variant in the ecoTEC Plus line, built for homes with higher hot-water demand. See the Vaillant ecoTEC Plus 832 boiler review.

Vaillant ecoFIT Pure. A newer, more budget-friendly range from Vaillant, aimed at smaller homes and straightforward installations. Full detail in the Vaillant ecoFIT Pure review.

Vaillant ecoFIT Pure 825. A mid-range output in the ecoFIT Pure line — as a general guide it suits typical two-to-three-bedroom homes, but check the review against your own property before deciding. See the Vaillant ecoFIT Pure 825 combi gas boiler review.

Vaillant ecoFIT Pure 830. A step up in output from the 825, for homes with slightly higher hot water demand. Full spec in the Vaillant ecoFIT Pure 830 boiler review.

Vaillant ecoFIT Pure 835. The highest-output model in the ecoFIT Pure range, built for larger homes with higher hot-water demand. Read the Vaillant ecoFIT Pure 835 review.

For a full side-by-side comparison, the Vaillant combi boiler reviews page covers the Vaillant models we've reviewed.

Glow-worm, Viessmann and Alpha Combi Boilers

Glow-worm Energy 30C. A value-focused combi from Glow-worm, built for smaller homes where budget is the priority without cutting corners on reliability. Read the Glow-worm Energy 30C boiler review.

Viessmann Combi Boilers. Viessmann sits at the premium end of the market, with a focus on build quality and longer component life. Viessmann combi boiler reviews, cost and installation guide covers pricing and what to expect from installation.

Alpha Combi Boilers. Alpha is a value-focused British brand, built for straightforward like-for-like replacements without the premium price tag. Read the Alpha combi boiler review for the full spec.

Which Brand Should You Choose?

There isn't a single "best" brand — there's a best brand for your budget, your property, and how long you want the warranty to run. As a general guide:

• Best on price: Baxi and Ideal tend to sit toward the more affordable end without sacrificing warranty length or build quality
• Best all-rounder: Worcester Bosch balances price, reliability and parts availability well, and is a widely recognised name in UK heating
• Best for longevity: Vaillant's ecoTEC Plus range has a strong reputation for durability, provided it's sized and serviced correctly
• Best for premium builds: Viessmann sits at the top of the market on component quality, at a matching price

If two brands are neck and neck on your shortlist, the deciding factor is often which one your installer services most often — faster parts, faster fixes, and an engineer who already knows the unit inside out.

Related Buying Guides on This Page

Alongside the combi boiler reviews above, we've included a few related pages that aren't combi boilers themselves but come up in the same buying journey: the Worcester Greenstar 18Ri review and the Vaillant ecoFIT Pure 418 boiler review, which both cover regular (heat-only) boilers suited to larger homes that already have a cylinder and tank, and the Worcester Bosch EasyControl review, which covers a smart heating control rather than a boiler. Worth a look if any of those fits how your home is set up.

Combi vs System vs Regular Boilers

Most models on this page are combi boilers, which heat water on demand with no tank or cylinder — the right choice for most flats and terraced houses in London. If your home has a separate hot water cylinder already, or you regularly run two showers at once, a system boiler paired with that cylinder can perform better under simultaneous demand. Our engineers can talk you through which setup suits your property when you book a survey.

Ready to Get Your New Boiler Installed?

Reading reviews only gets you so far — the right boiler for your home depends on your current system, your pipework, and how many bathrooms you're running. Two homes on the same street with the same layout can still need different output, depending on insulation and how the existing pipework is routed. Our engineers can confirm the right output for your property and talk you through a personalised quote before any work starts.

Get a personalised boiler installation quote in London from Serviceteam's Gas Safe registered engineers. We install all the brands and models covered on this page, and every installation comes backed by our own workmanship guarantee on top of the manufacturer's warranty.