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Vaillant ecoTec Plus 835 Combi Boiler – Review

In today’s review, we’ll be taking you through what the Vaillant ecoTec Plus 835 has to offer. The 835 is a popular choice for those with small to mid-sized properties, due to the increased flow rate and output over its smaller boilers. Founded in Germany in 1874, Vaillant is Europe’s second largest boiler manufacturer, while directly competing with Worcester Bosch. High quality and polished German-engineered energy products all sit within Vaillant’s product lines.

In today’s review, we’ll be focusing on the Vaillant ecoTec Plus 835 combi boiler.

Will the Vaillant ecoTec Plus 835 be suitable for my home?

The Vaillant ecoTec Plus 835 can supply enough hot water for homes with up to 3 bedrooms and 2 bathrooms with a bath or shower installed. The 835 offers a central heating output of 30.4kW and hot water output of 35kW, which is enough for small to mid-sized properties. You’ll also benefit from an improved flow rate over the 835 at 14.3l/m, which offers a better heating and hot water experience.


The ecoTec Plus 835, like many other combination boilers, has a standard control panel installed on the front of the boiler which is hidden by a flap. The boiler controls allow you to change the output of the boiler, as well as switch the boiler on/off. The display on the front will also give you diagnostics including fault codes if something has gone wrong with the boiler. Fault codes displayed on the boiler make it easier for engineers to be able to diagnose the problem quickly, without needing to open up the boiler and investigate first. Modern boilers are more straightforward to diagnose which reduces call-out fees.

Seeing as the controls on the boiler will not be sufficient to allow you to take full advantage of your central heating system. Vaillant offers a range of boiler controls from mechanical to smart thermostats. Smart thermostats are a modern and techy alternative to the traditional programmable thermostat, allowing you to control your heating and hot water from your smartphone, tablet or PC.

Smart thermostats come bundled with an app that can be installed on a smartphone or tablet. The app will allow you to alter your heating settings, monitor your energy use, and switch your heating on or off whether you’re at home, or away with a WiFi/3G & 4G connection. If you’re not sure about smart thermostats yet there are still wireless programmable thermostat options available.


The Vaillant ecoTec Plus 835 measures at 720x440x372mm which isn’t the most compact, especially for kitchen cupboards. If you require a boiler that can fit in a kitchen cupboard or a tight space, the Worcester Greenstar 30Si Compact is a great choice.


The ecoTec range comes bundled with a standard 5-year warranty free of charge for your extra peace of mind. However, if you decide to install with Hometree, you can benefit from an extended warranty of up to 10 years.

Energy Efficiency

The ecoTec Plus 835 is a highly efficient combination boiler, with an ErP (Energy-related Products) rating of 89.3% (A-grade). In addition to superb performance, you will reduce your carbon footprint once the boiler is on the wall, as well as make a saving on your energy bills.

The ErP directive actively tests energy products to ensure that all energy products pass certain criteria for performance and efficiency that they pass specific standards for performance and efficiency. If a boiler is tested and fails the tests, the directive will step in to recommend design improvements to reduce the amount of energy wasted, thus reducing carbon footprint.


The Vaillant ecoTec Plus 835 is an excellent choice for small to medium-sized homes, especially if you have one to two bathrooms with a bath installed and up to 3 bedrooms. The ecoTec Plus range offers boilers high-efficiency and excellent performance while reducing your carbon footprint. The ecoTec Plus boiler range has been awarded QuietMark status for its low noise output and design.

 Vaillant ecoTec Plus 835
ErP rating (energy efficiency)A (89.3%)
Size (HxWxD in mm)720x440x372
Heating output (kW)30.4
How water output (kW)35kW
Flow rate (litres/min)14.3
Standard warranty (years)5 (extended warranties available)
Other available sizes (kW)25, 32, 38

Which? boiler review

The consumer group Which? review each boiler on the market to find the most (and least) reliable boilers according to a survey completed by thousands of boiler owners. In each review, Which? supply a brand score percentage and star ratings for each category. Take a look at the Vaillant ecoTec Plus 835 ratings below:

Which? Score 
Efficiency rating★★★★★
Brand reliability★★★★☆
Brand customer score★★★★★
Ease of repair★★★★★
Ease of service★★★★★
Availability of parts and spares★★★★★
Build quality★★★★★
Engineer recommendation★★★★★
Brand score80%

Boiler manual

Vaillant ecoTec Plus 835 Combi boiler manual

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