Which is the Best Combi Boiler?

The best Combi boilers on the market are the Worcester Bosch Greenstar i, the Vaillant ecoTEC Plus and the Ideal Logic+. Year after year, these boilers continue to dominate both homeowner and installer surveys as the most reliable, energy efficient and high performance boilers available today. These boilers are designed for indoor, wall-mounted installation.

The boilers are available in a range of outputs to suit homes of most sizes from 1 bedroom flats to 4 bedroom houses. A professional installer will be able to recommend the best boiler for your home but to help you narrow down your search we’ve put together some guidelines based on industry recommendations:

Number of Bedrooms Number of Bathrooms Number of Radiators Recommended Output Which Boilers?
1 – 2 1 Up to 10 24 – 27kW Worcester Bosch Greenstar 25i
Vaillant ecoTEC Plus 25kW
Ideal Logic+ 25kW
2 – 3 2-3 Up to 15 28 – 34kW Worcester Bosch Greenstar 30i
Vaillant ecoTEC Plus 32kW
Ideal Logic+ 30kW
4+ 3+ Up to 20 35 – 42kW Vaillant ecoTEC Plus 35kW or 38kW
Ideal Logic+ 35kW

Note: For larger properties with 4 or more bedrooms, multiple bathrooms, lots of inhabitants or a particularly high need for hot water, a professional engineer may recommend a System or Regular boiler rather than a Combi as these include a backup supply of a hot water cylinder.

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About the Boilers

Combi boilers are the most commonly installed type of boiler in the UK for a number of reasons.

While System and Regular boilers require a hot water storage cylinder, a Combi boiler is an all-in-one unit which will produce hot water for central heating and your taps. This saves a great deal of space in your home and often means it can be tucked away in a kitchen cupboard. With no water tank or cylinder needed it also results in a simpler and faster installation.

It takes its water supply directly from the mains which usually results in a stronger pressure. A Combi boiler gives you the luxury of hot water on demand so there’s no need to worry about running out and having to wait for the tank to refill.

Brand / Model Available Outputs (kW) Dimensions (mm) Efficiency Average Price
Worcester Bosch Greenstar i 25, 30 710 x 400 x 330 94% £800-£950
Vaillant ecoTEC Plus 25, 32, 35, 38 720 x 440 x 340 89.4% £1000-£1400
Ideal Logic+ 25, 30, 35 700 x 395 x 278 94% £700-£900

Want to compare these boilers in more detail? Check out our Comparison Tool to find the best boiler for your home.

Worcester Bosch Greenstar i
Worcester Bpsch Greenstar i
According to Worcester Bosch, this is their most popular Combi boiler. It has been awarded a Which? Best Buy Award for 7 years running and regularly tops both homeowner and installer polls for reliability and performance. In addition, the brand currently holds the Royal Warrant to supply heating to the Royal Family.

While the Worcester Bosch model we’ve featured here is a gas boiler which best suited to small or medium sized homes, Worcester Bosch manufacture a wide range of boilers to suit almost every home. For example, the Greenstar CDi Highflow is a Combi boiler designed for larger homes with 2 bathrooms and they also produce oil boilers, System boilers and Regular boilers.

Key features:

  • Simple boiler controls with clear information display
  • Zero risk of condensate pipe freezing in severe weather
  • Wide choice of controls including mechanical, digital and smart (Wave by Worcester Bosch)
  • Compact design for kitchen cupboard installation
  • Low energy pump reduces electrical usage
  • LPG convertible
  • Which? Best Buy Award for 7 years running
  • Achieves an A+ ErP package efficiency rating for heating when installed with a Wave smart internet connected control
  • Fills a standard kitchen sink in 45 seconds
  • Solar compatible

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Vaillant ecoTEC Plus

Vaillant ecoTEC Plus combi gas boiler

Vaillant have been producing heating systems since 1874. Today they boast German engineering combined with UK manufacturing. This boiler is Vaillant’s ‘flagship’ model and offers the highest output of the boilers we’ve selected at 38kW so it’s a great choice for larger homes with a high demand for hot water. This boiler includes a 5 year warranty as standard with 7 or 10 years available when installed by a Vaillant accredited installer.

Vaillant also produce a range of other Combi, System and open-vent boilers to suit a range of homes and lifestyles.

Key features:

  • Rapid hot water delivery in just 5 seconds
  • Awarded Which? Best Buy 2017
  • Wide modulation range of up to 1:6 results improves energy efficiency
  • Flame lift detection system enables quieter combustion
  • Stylish contoured case design
  • Two-stage frost protection built in
  • Quiet Mark accreditation
  • Designed for quick installation
  • Compatible with aroTHERM air to water heat pump hybrid system
  • LPG convertible
  • Range of controls including wired, wireless and smart (vSmart by Vaillant)

Ideal Logic+

Ideal Logic Plus combi gas boiler
This manufacturer has been designing high quality boilers in the UK for over 100 years. In addition to the quality, they offer real value for money when compared to some other brands and are a popular choice for many homeowners and installers.

The Logic+ boiler by Ideal includes a 7 year parts and labour warranty with an impressive 10 year warranty on the heat exchanger. The range is endorsed by the Energy Saving Trust and received both the Queen’s Award for Enterprise 2013 and Good Housekeeping Reader Recommended Status in 2013 and 2017. In addition to their range of Combi boilers, Ideal also manufacture System and Regular boilers for homes in need of a hot water cylinder.

Key features:

  • 10 year warranty on heat exchanger
  • Compact cupboard fit
  • Low lift weight for easier installation
  • Wide range of additional flueing options
  • Large digital display
  • Includes PRV wall outlet pipe
  • Fully modulating operation to low outputs
  • Concealed pipe connections
  • Includes boiler frost protection
  • Pre-wired mains lead
  • Preformed copper tails
  • Universal condensate connection
  • LPG conversion kit available on 30kW model

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