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Vaillant ecoTec exclusive Green iQ 843 Combi Boiler - Review

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In this review, we’re looking at the Vaillant ecoTec exclusive Green iQ 843 Combi. As the most powerful model in Vaillant’s ecoTec exclusive range, it is very popular with large households that have high hot water demands. Here we’ll give you a rundown of everything you need to know about the ecoTec 843 Combi to help you determine whether it’s the right choice for your boiler replacement.

Before we get into the nitty-gritty, let’s first introduce you to Vaillant. For those who don’t know, Vaillant is the leading German boiler manufacturer, best known for its precision engineering. The company has long played an essential role in the heating industry, having developed water heaters in the early 1900s and combi boilers in the early 1960s.

Today, Vaillant continues to excel in innovation. Their ecoTec boilers are the first to be built with eco-friendly and 85% recyclable materials. They’re also fully compatible with the Vaillant vSMART thermostat, along with other popular models like the Nest, Hive and Honeywell Lyric T6 (a smart thermostat Hometree offers for free with every boiler installation.) With smart control features and outstanding performance, the Vaillant ecoTec exclusive 843 stands out as a boiler that you can rely on to meet high heating and hot water demands.

Will the Vaillant ecoTec 843 be suitable for my home?

As we mentioned previously, the ecoTec exclusive 843 is designed to heat large, spacious households with 15-20 radiators efficiently. So we’re talking detached and semi-detached houses, with at least 4 bedrooms and 2 bathrooms. We think you’ll agree, that’s pretty impressive!

The Vaillant ecoTec has a powerful central heating output of 43kW and excellent hot water flow rate of 17.8 l/min. This is the key difference between this model and the Vaillant ecoTec exclusive Green iQ 835, which only has a 14.5 l/min flow rate. If you have a large, busy household with two showers and a bath and you need hot water fast, the Vaillant 843 is the obvious choice.

It’s worth noting that you will need high water pressure for the Vaillant ecoTec 843 to work to its highest capacity. It’s important to get your water pressure tested before choosing a new boiler, which can be done remotely without an engineer visit.

If you’re running a large household but perhaps don’t need the fast flow of hot water the 843 offers, you may find the Vaillant ecoTec iQ 835 meets your needs sufficiently. This combi boiler from Vaillant’s ecoTec exclusive range is slightly smaller in size (406mm compared to the 843’s 474mm) but still capable of powering 15-20 radiators with its 35kW output.

If you’re looking to compare the Vaillant ecoTec combi with an alternative brand, we recommend looking at the Worcester Bosch Greenstar 42CDi Classic. It offers a similar flow rate of 17.2 l/min; however, the central heating output is much lower at just 30kW.

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Vaillant ecoTec exclusive Green iQ 843 Controls

Like most boilers, the Vaillant green iQ 843 has basic operator controls, with an LCD screen and buttons located under the front flap. It’s all relatively straightforward and something our Gas Safe engineers can go through with you at home.

Did you know that all boilers must now comply with the Boiler Plus regulations that came into force in April 2018? To put it simply, boilers must meet certain levels of efficiency (ErP). They must also have time and temperature controls fitted that are working correctly.

Combi boilers like the Vaillant ecoTec 843 must also have 1 of these 4 features:

Weather compensation: The ability to alter water temperature based on the temperature outside

Load compensation: The ability to alter the temperature of the hot water produced by the boiler based on room temperature

Smart control: Central heating automation to optimise your system for greater efficiency

Passive Flue Gas Heat Recovery Device: Uses otherwise lost flue glasses to heat water in a boiler

The Vaillant ecoTec combi boiler has a Passive Flue Gas Heat Recovery Device built into its system, so you can tick that last one off without even trying.

We do, however, highly recommend installing a digital or smart thermostat in your home and linking your boiler to a smart controller. Vaillant offers a number of intelligent solutions including the VRC 700 / 700f Weather Compensating Thermostat and vSMART™ smart thermostat, both of which will ensure compliance with Boiler Plus.

The Weather Compensating Thermostat is available wired or wireless and is compatible with the ecoTec 843. It will maximise your boiler’s performance and comes with a number of useful features such as flexible time programs and holiday programs.

Vaillant’s vSMART™ heating control app is also compatible with the ecoTec exclusive with green iQ combi boilers. You can download it on your smartphone or tablet and use it to gain full control of your heating and hot water, no matter your location. As the name suggests, it’s a really intelligent app that will even learn your preferences and heating needs to ensure your system offers the highest levels of efficiency.

Just to put it out there, you don’t have to go with a Vaillant product. Most gas boilers, including the ecoTec 843, are also compatible with popular smart thermostats like the Nest and Hive, or the popular Honeywell Lyric T6 thermostat you can get free with your Hometree boiler installation. Both offer easy-to-use controls on the devices and their smartphone apps, so you can gain better control of your system, whether you’re at home or away.

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ecoTec 843 combi size

The Vaillant 843 is a pretty powerful boiler, so it’s no surprise that it’s a little on the large size. At 720x440x474mm it may be a little too big to fit in your average kitchen cupboard (unless your willing to have something custom made.) A utility room is an obvious location for a boiler like this.

If you don’t have space or are looking for something a little more compact, we’re afraid you may have to compromise on output and flow rate. Vaillant has a fantastic range of ecoFIT pure combi boilers, which are lightweight and compact in design. They’re suitable for homes with two bathrooms but have a slightly lower output of 35kW and flow rate of 14.1 l/min.

Vaillant ecoTec Green 843 warranty

Choose Hometree for your Vaillant ecoTec 843 installation and receive a standard 5-year warranty. This can be doubled to a 10-year warranty for an additional charge. We are a Which? Trusted Trader and have been rated Excellent on Trustpilot, so you can enjoy peace of mind that we’ll carry out your boiler installation to the highest standards.

ecoTec exclusive 843 energy efficiency

The ecoTec exclusive has a fantastic ErP rating (previously known as SEDBUK) of 89.6%. Just in case you’re wondering what we’re talking about, ErP stands for Energy-related Products and is a system for determining a boiler’s energy efficiency. An 89.6% rating gives this boiler an A rating, one of the highest ratings you can get. The good news is that by replacing your old boiler with a brand new A rated model, you should see a decrease in your energy bills.

Verdict - Is the Vaillant ecoTec exclusive Green iQ 843 the best boiler for your home?

The Vaillant ecoTec 843 is an excellent choice for family homes, requiring high central heating and hot water outputs. The fast hot water flow rate puts it head and shoulders above the rest for busy households, and its eco-friendly credentials are a benefit to all.

Swap your old boiler for the Vaillant ecoTec 843 green iQ combi today, and benefit from greater heating efficiency at a lower cost. It’s a smart decision to make. 23We hope our Vaillant green iQ review has answered all your questions, but if you’d like to speak to one of our experts, please don’t hesitate to get in touch.

 Vaillant ecoTec exclusive Green iQ 843
ErP rating (energy efficiency)A (89.7%)
Size (HxWxD in mm)720x440x474
Heating output (kW)43
Flow rate (litres/min)17.8
Standard warranty (years)5 (extended warranties available)
Other available sizes (kW)35

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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 exclusive Green iQ 843 Combi boiler 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 exclusive Green iQ 843 Combi boiler manual