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Which is the Best Combi Boiler? Vaillant vs Viessmann


Vaillant and Viessmann are popular boiler brands with both homeowners and heating engineers. Both brands manufacture regular, system and combi boilers in a wide range of models and sizes, but the best selling range for each is Vaillant’s ecoTEC plus and Viessmann’s Vitodens 050-W.

But is one boiler better than the other? We compared both boilers in their key features to help you decide on the best choice for your home.

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What do the boilers have in common?

Both the Viessmann Vitodens and ecoTEC plus are wall-mounted combi boilers for homes connected to the gas grid (but they can be converted to run on LPG for off-grid homes). Although it’s best to ask a Gas Safe registered engineer to recommend the best size boiler for your home, the 35 kW output model is generally best suited to homes with 3-4 bedrooms.

These models are both combi boilers which means they are an all-in-one compact unit with no need for a hot water cylinder or tank in the attic. This is because combi boilers take their water supply directly from the mains and will produce hot water for both radiators and taps on demand.

ManufacturerVaillantViessmann
ModelecoTEC plus 835 35kW Combi Gas BoilerVitodens 050-W 35kW Combi Gas Boiler
ErP Energy RatingA (up to 93%)A (up to 93%)
NoX EmissionsClass 5 (best)Class 5 (best)
Maximum flow rate litres per min14.314.1
Hot water temp controls?YesYes
Concealed user controls?YesNo
Standard warranty5 years3 years (10 year warranty on heat exchanger)
Extended warranty availableVaillant Advance installers can offer extended warranties of 7 or 10 yearsViessmann trained installers can offer extended warranties of up to 7 years
LPG Convertible?YesYes
Dimensions (mm)707 x 400 x 350720 x 440 x 372

Features and Benefits

Vaillant ecoTEC plus 835 35kW Combi Gas Boiler

  • User-friendly backlit display with simple push button programming.
  • Stainless-steel heat exchanger delivering high fuel efficiency and reduced corrosion.
  • Quiet Mark accreditation which is awarded to manufacturers of products with quiet operation.
  • Wide range of heating control options including the vSMART™ thermostat and smartphone app.
  • Can deliver hot water within 5 seconds with no need for a hot water storage cylinder.
  • Features built-in frost protection to keep the boiler working throughout winter when it’s needed most.
  • Viessmann Vitodens 050-W 35kW Combi Gas Boiler

  • A rated, high-efficiency modulating pump (range up to 1:4).
  • Stainless steel Inox-Radial heat exchanger and cylinder burner for high efficiency and reduced corrosion.
  • Suitable for installation in smaller living areas thanks to compact dimensions and recessed fittings.
  • Easy to service thanks to serviceable parts such as the heat exchanger being located at the front.
  • Includes electronic boiler control unit for thermostatic mode, frost stat and weather compensated mode.
  • Outside temperature sensor available as an extra accessory.
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    About the brands

    Viessmann UK and Vaillant UK are both part of international groups (Viessmann Group and Vaillant Group). Both began in Germany. Despite having operations in more than 20 countries across the world and a history spanning over 140 years, Vaillant started as and remains a family-owned business. Viessmann has been operating for over 100 years.

    Which boiler offers the best warranty?

    In terms of standard warranty, Vaillant offers the longer option at 5 years compared to the 3 years offered by Viessmann. However, Viessmann also includes a 10 year warranty on the heat exchanger which is a major component.

    If you have your Viessmann or Vaillant boiler installed by an engineer who is accredited by the brand, you could receive an extended warranty of up to 10 years.

    Which controls are available?

    If you are looking for a simple analogue timer or a programmable room thermostat, both boilers will work for you. However, if you want smart controls the Viessmann 050-W Combi boiler is not the choice for you. While some Viessmann boilers are available with smart controls (such as the Vitodens 100W or 200W) this particular model is not.

    The Vaillant ecoTEC plus, on the other hand, does work with the vSMART™ app based heating control. This technology not only enables you to operate the boiler from a smartphone even when you are not at home (or in the country!)

    How much do the boilers cost?

    Of the two boilers, you are likely to pay around £300-£400 more for a Vaillant boiler than a Viessmann. The Vaillant ecoTEC plus 35 kW costs £1,200 – £1,400 on average while the Viessmann Vitodens 050-W 35 kW costs around £900 – £1,200.

    It’s important to remember, however, that these prices are for the boiler itself and do not include the cost of installation. To get the best price for a new boiler installation, it’s best to find at least 3 quotes from different so you can compare and get the best deal.

    Vaillant vs Viessmann: Which is the best combi boiler?

    Vaillant is the more costly option, but this is reflected in the extra features offered when compared to the Viessmann model. The Vaillant provides a slightly higher flow rate, smart control option, Quiet Mark accreditation and, crucially, the longer standard warranty. However, for less money you can get the Viessmann Vitodens which is still a high quality boiler in a slightly more compact design. It also includes the 10 year warranty on the heat exchanger which definitely something to keep in mind.

    Whichever boiler you choose, you can rest assured that you are investing in a powerful and efficient boiler by a brand with an excellent track record with both homeowners and engineers.

    To ensure you make the right choice for your home in terms of type of boiler (combi, system or regular) and in the correct size, contact Gas Safe registered heating engineers for professional advice. Get in touch with Boiler Guide and request free boiler quotes today. They will put you in touch with up to 3 Gas Safe engineers who will recommend the best boiler for your home and provide free, no-obligation quotes for its supply and installation.

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