Best Gas Combi Boilers

Overview

From long-established UK manufacturer Worcester Bosch, the Greenstar i range built on the success of the earlier i Junior models and became one of the UK’s best-selling gas combi boiler lines.

Offering A-rated efficiency (around 94%) and hot water flow rates of up to 12.3 litres per minute (30i model), the Greenstar 25i and 30i delivered strong all-round performance at a competitive price point — helping them become firm favourites with homeowners and installers alike.

While newer Worcester Bosch models are now available, the Greenstar i range remains a solid and dependable choice, particularly where budget and proven reliability are key considerations.

Is the Greenstar 25i or 30i right for my home?

The Greenstar i range is available in two outputs:

• 25i – suited to smaller homes with modest hot water demand
• 30i – higher output, better suited to homes with greater hot water use

Both models are capable of comfortably heating one to three bedroom homes, but the 30i offers improved hot water performance — making it a better choice where multiple outlets may be used in close succession (for example, running a bath while using taps).

While neither model struggles with day-to-day heating demands, homeowners with higher hot water usage may prefer the added capacity of the 30i.

Size and installation

Both models measure 330mm in depth, meaning they are not the most compact boilers on the market. Where cupboard space is limited, Worcester Bosch also offers slimmer alternatives within its wider Greenstar range.

Installation is straightforward for most properties and parts availability remains excellent due to the popularity of the range.

Reliability and support

One of the Greenstar i range’s biggest strengths is long-term reliability. Worcester Bosch has consistently been rated highly for:

• Build quality
• Reliability
• Installer recommendation

These models have historically received Which? Best Buy status, reflecting strong performance and owner satisfaction.

Verdict

The Worcester Bosch Greenstar 25i and 30i remain reliable, well-proven gas combi boilers, particularly suited to small and medium-sized homes.

However, they are now best viewed as a value-focused, established option, rather than Worcester Bosch’s most advanced offering. Homeowners seeking the latest design features, quieter operation, or improved modulation may wish to consider newer Worcester Bosch ranges.

That said, for buyers prioritising proven reliability, widespread installer familiarity, and competitive pricing, the Greenstar i range continues to be a sensible and dependable choice.

Did you know? Worcester Bosch has consistently ranked among the top boiler manufacturers in independent surveys, scoring highly for build quality, reliability, and installer recommendation — one of the key reasons the Greenstar i range became such a UK best-seller.

Specification

Please select a model below to view its specifications.

• Greenstar 25i
• Greenstar 30i

Overview

From German manufacturer Viessmann, the Vitodens 100-W is one of the most widely recommended gas combi boiler ranges in the UK, known for excellent build quality, long service life, and strong efficiency.

The 100-W range has earned a reputation for delivering premium engineering at a competitive price point, making it a popular alternative to UK brands for homeowners who value efficiency, quiet operation, and reliability.

Is the Viessmann Vitodens 100-W right for my home?

The Vitodens 100-W range is well suited to homes where space, efficiency, and noise levels are important considerations.

Key benefits include:

• Compact footprint – smaking it ideal for kitchen cupboards
• High seasonal efficiency – A-rated
• Very quiet operation – with noise levels typically around 46–47 dB

This makes the Vitodens 100-W a strong choice for flats and smaller to medium-sized homes, as well as properties where the boiler is located close to living or sleeping areas.

Output options and suitability

The Vitodens 100-W series is available in multiple outputs, typically:

Benefits include:

• 26kW
• 30kW
• 35kW

Smaller homes with 1–3 bedrooms and one bathroom are usually well matched to the 26kW or 30kW models, while larger homes with higher hot water demand may benefit from the 35kW version.

As always, final sizing should be confirmed by a qualified Gas Safe engineer to ensure adequate hot water performance.

Efficiency and technology

The Vitodens 100-W uses Viessmann’s Inox-Radial stainless steel heat exchanger and MatriX burner technology, which are key reasons for its strong reputation.

Benefits include:

• High real-world efficiency
• Long component lifespan
• Consistent combustion and performance

These features help reduce running costs while maintaining excellent reliability over time.

Size and installation

With a depth of approximately 350mm, the Vitodens 100-W is one of the more compact gas combi boilers in its class and fits comfortably inside most standard kitchen cupboards.

Its lightweight design and straightforward connections also make installation relatively simple for most properties.

Warranty and reliability

Viessmann is consistently rated highly for build quality and reliability. When installed by a Viessmann-approved engineer, the Vitodens 100-W can be supplied with a warranty of up to 10 years, offering long-term peace of mind.

Verdict

The Viessmann Vitodens 100-W remains one of the best all-round gas combi boilers available, particularly for homeowners who want:

• Compact size
• Quiet operation
• Excellent efficiency
• Proven long-term reliability

While newer premium models exist, the Vitodens 100-W continues to strike an outstanding balance between performance, quality, and value, earning its place as a go-to gas combi boiler for UK homes.

Did you know? Viessmann has consistently achieved top scores in independent surveys for build quality, reliability, and engineer recommendation. The Vitodens 100-W range has also received Which? Best Buy recognition, reinforcing its strong reputation among homeowners and professionals alike.

Specification

Please select a model below to view specifications.

• 26kW
• 30kW
• 35kW

Overview

From German manufacturer Vaillant, the ecoTEC Plus 832 built on the success of the earlier ecoTEC models and became one of the UK’s most popular mid-output gas combi boilers.

Designed to deliver strong hot water performance, quiet operation, and dependable efficiency, the ecoTEC Plus range has long been favoured by both homeowners and heating engineers. While Vaillant has since introduced newer ranges, the ecoTEC Plus 832 remains a well-regarded and widely installed option.

Is the Vaillant ecoTEC Plus 832 right for my home?

he ecoTEC Plus 832 offers a balanced output that suits many typical UK homes.

• Heating output – approx. 24–25kW
• Hot water output – 30kW
• Hot water flow rate – around 13 litres per minute

This makes it well suited to small to medium-sized homes, typically:

• 2–4 bedrooms
• One main bathroom with a bath and shower
• Light to moderate simultaneous hot water use

For households with higher peak demand or multiple bathrooms in use at once, a higher-output model may be more appropriate.

Efficiency, controls and technology

The ecoTEC Plus 832 is ErP A-rated for energy efficiency and uses Vaillant’s proven condensing boiler technology to reduce fuel consumption compared with older non-condensing models.

Key features include:

• Modern pump technology for improved efficiency
• Clear front-mounted display showing operating status and fault codes
• Compatibility with Vaillant smart controls, allowing remote control of heating and hot water via smartphone, tablet, or PC (with compatible accessories)

While older efficiency metrics such as SEDBUK are no longer used, the ecoTEC Plus range continues to meet current energy efficiency standards.

Quiet operation

One of the standout strengths of the ecoTEC Plus range is quiet performance. The 832 model carries Quiet Mark certification, making it a good choice for properties where the boiler is installed near living or sleeping areas.

Size and appearance

With a depth of approximately 338mm, the ecoTEC Plus 832 is compact enough to fit inside most kitchen cupboards.

Vaillant’s contoured casing and drop-down control flap help the boiler blend neatly into its surroundings, whether installed in a cupboard or left visible.

Warranty and reliability

Vaillant boilers have a long-standing reputation for reliability and build quality. The ecoTEC Plus 832 is typically supplied with a standard manufacturer warranty, which can often be extended when installed by a Vaillant Advance-approved engineer.

Verdict

The Vaillant ecoTEC Plus 832 sits neatly between lower-output 30kW combi boilers and larger 35kW models, offering strong hot water performance without the cost or size of higher-output units.

While newer Vaillant models are now available, the ecoTEC Plus 832 remains a dependable and well-proven choice for homeowners looking for:

• Quiet operation
• Solid efficiency
• Good hot water flow rates
• Trusted brand support

For small to medium-sized homes, it continues to justify its place among the best gas combi boilers available.

Did you know? Vaillant has consistently scored highly in independent surveys for build quality and reliability, and the ecoTEC Plus range has previously received Which? Best Buy recognition — one of the reasons it remains popular with installers and homeowners alike.

Specification

Whilst our write-up focuses on the 32kW model there are however alternative kW models available—please select a model below to view its specifications.

• 25kW
• 32kW
• 35kW
• 38kW