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Baxi 400 Combi

The Baxi 400 Combi is a modern condensing gas boiler that offers you the option to control your heating via a smartphone or tablet.

Available in two heat outputs, the Baxi 400 Combi is ideal for small and medium households requiring a boiler that is small enough to fit inside a kitchen cupboard. It has achieved an A efficiency rating and is set up for use with a smart room thermostat that enables you to control the boiler, regardless of whether you’re at home or away. What’s more, this boiler comes with a decent parts and labour warranty.

How Much Does this Boiler Cost?

The Baxi 400 Combi can be purchased with an output of 24kW or 28kW, and prices vary between £620 and £690. If you need the higher output model, you can expect to pay the top end of the boiler’s price range. Whichever model you require, it’s important that you also factor in the cost of installation because this can often be more than the price of the boiler. As supplier and installer rates vary as well, we suggest you shop around to see if you can find any great deals before handing over any cash.

How will I know if this Boiler is Suitable for My Home?

Baxi’s 400 Combi doesn’t need any additional loft tanks or a separate hot water cylinder, making this boiler a fantastic option for apartments or houses where space is an issue. It probably isn’t the best for properties with multiple bathrooms because combi boilers struggle to cope when two showers are running simultaneously. This series does, however, include two heat outputs (sizes), making it suitable for small and medium homes.

Prior to purchasing this boiler (or any other boiler), you should ask a Gas Safe registered engineer to take a look around your home and assess your unique requirements so that they can recommend the correct boiler type and size for your needs.

Is it a High Efficiency Boiler?

Yep. Just like most modern condensing gas boilers, the Baxi 400 Combi is a highly efficient boiler that can help to cut the cost of your energy bills. It has a seasonal efficiency of 89% and falls into the A rating band. Not only is the boiler Energy Saving Trust recommended as it comes but it’s also compatible with the smart uSense room thermostat that lets you operate the boiler using a smartphone or tablet. Additionally, the uSense control allows you to keep an eye on how much energy you’re using to help you save more money on those bills.

Does this Boiler have a Good Range of Controls and Features?

This boiler has a good range of controls that are located on the front of its casing, such as an operating mode selector and switches that enable you to adjust the hot water and central heating temperatures. It comes with a fault diagnosis LCD display that shows you the boiler temperatures and current status. If you’re not interested in the optional smart control, you can choose from a selection of other accessories including mechanical timers and plug-in RF thermostats. The boiler also has an inbuilt frost thermostat and is supplied with a hanging bracket and different flue lengths.

How long is the Warranty on this Boiler?

If you decide to purchase the Baxi 400 Combi for your home, you’ll receive a lengthy 5-year parts and labour warranty as standard.

Baxi 400 Combi By Size and Price

ModelTypeDimensionsMaximum Flow RateOutputEfficiency RatingTypical Price
400 Combi 24CombiH – 700 mm
W – 395 mm
D – 279 mm
11.5 l/min24 kWA 90% and above£620
400 Combi 28CombiH – 700 mm
W – 395 mm
D – 279 mm
11.5 l/min28 kWA 90% and above£690

Summary of Important Information

  • Priced between £620 and £690
  • Heating output of 24kW or 28kW
  • Hot water flow rates of 9.8 or 11.5 litres per minute
  • Dimensions of 700mm (H) x 395mm (W) x 279mm (D)
  • Uses gas as its fuel source
  • A-rated for efficiency
  • Smart compatible
  • 5-year warranty as standard

Pros and Cons

The energy efficient Baxi 400 Combi boasts many advantages and can be installed virtually anywhere within your small or medium-sized property. Baxi doesn’t have the best overall Which? score, though. Below, we’ve shared a list of pros and cons to help you figure out if this combination boiler is right for you and your home.


  • Fits in a kitchen cupboard
  • Suited to flats and small to medium-sized houses
  • No need for separate cylinder or loft tanks
  • Easy to use and service
  • NOx Class 5 boiler – kinder to the environment
  • Provides maximum energy efficiency – reduce fuel bills and carbon emissions
  • Compatible with uSense smart room thermostat – can monitor your energy use and control your heating using a smartphone or tablet, wherever you happen to be
  • 5-year parts and labour warranty


  • Baxi boilers have and overall Which? score of 54%
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