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In this Vaillant flexoTHERM 400V + aroCOLLECT air source heat pump review, we look into its specs, features, benefits and price so you can decide whether it’s the right system for you.
German company Vaillant was founded in 1894 and has already been a leader in heating technology innovation. Vaillant’s extensive range of ground and air source heat pumps allows homeowners to lower their carbon footprint and energy bills.
The flexoTHERM is one of Vaillant’s most innovative and sustainable ground source heat pumps as it can be combined with the aroCOLLECT module to harness energy from the air, too. Below, we delve into its features and benefits to help you assess whether it’s the right fit for your home.
The Vaillant flexoTHERM 400V is a quiet and highly efficient ground source heat pump. The added aroCOLLECT brine collector module adapts it to work as an air source heat pump by using energy from air to heat brine. The module uses the ambient air temperature to warm the fluid (in this case, brine) like a ground loop system would. This results in higher air-to-water efficiency, as it prevents heat loss between your indoor areas and the outside. aroCOLLECT features a twin unit connector that uses balanced Tichelmann piping. The reverse return system is also ideal for outdoor use in commercial, agricultural and residential projects.
The pump offers optimum performance and efficiency, being rated A+++ for energy efficiency. The flexoTHERM range also incorporates a state-of-the-art compressor technology called electronic vapour injection (EVI), which can help the system deliver the highest levels of heating performance.
Due to its high power output of 19kW, this heat pump system is ideal for residential projects and larger dwellings or developments. One of its main advantages is that the base system can connect to 3 different sources of energy: water, ground and air.
The aroCOLLECT module is only available with the 400V flexoTHERM pump, and comes in power outputs of 5, 8, 11, 15 and 19kW. You can cascade up to 7 of these models to scale the power of your heat pump.
This heat pump is QuietMark certified and is reported to be one of the quietest air source heat pump models on the market, so you can expect minimal sound disruption in your home.
The system features a set of intelligent weather-compensating controls and is fully compatible with Wi-Fi. This also means that the heat pump can be operated remotely. The flexoTHERM range is also compatible with the Vaillant wired VRC 700 and wireless VRC 700f controls. You can manage the heat pump using a clear digital display that shows, in real time, how much heat is being absorbed or used.
Installing the Vaillant flexoTHERM 400V and aroCOLLECT is very straightforward. Many integral components are already included in the system, such as ground and heating circulation pumps and a 3-way diverter valve. There is also a wide range of accessories available to complete your setup such as water heat exchangers and brine filling stations.
The Vaillant flexoTHERM 400V costs around £5,300, and with the addition of the aroCOLLECT module, the price is likely to increase to around £11,000 depending on the installer you opt for. This air source heat pump is among the most expensive on the market, but considering its great power output and efficiency, we think it’s worth the price tag.
As of October 2025, Vaillant is rated an impressive 4.6 stars out of 5 on Trustpilot from over 22,000 reviews. While not all the comments are about its heat pumps specifically, it is a great reflection on the company’s products and customer service.
“Great communication. Swift diagnosis of fault and part replaced right away. Whole process from booking to completion of works provided high quality customer service. Engineer ref: #629.”
“Engineer No. 829 (Nick) visited to fix my heat pump. He was knowledgeable, helpful, phoned before his arrival and sorted out the problem quickly – he provided excellent service. My only issue was with the prior organisation of his visit as my first appointment wasn’t booked properly on the system, but a replacement appointment was made for the following day so overall I was happy with the service I received.”
“The installment of the heat pump was amazing considering this is an old house with thick walls. The hot water system and the pump have worked flawlessly so far though we haven’t gone through a winter yet.”
The Vaillant flexoTHERM 400V is an innovative and highly efficient heat pump, which can harness energy both from the ground and from the air thanks to the aroCOLLECT module. It comes in a wide range of power outputs and you can opt to cascade several heat pumps for even more power.
It’s certainly not the cheapest on the market, but it’s also the among the most efficient; the considerable energy bill savings will enable you to recoup your initial investment sooner.
We considered several factors when reviewing the Vaillant flexoTHERM heat pump, including the following weighted criteria: design (20 per cent), durability (20 per cent), efficiency (25 per cent), performance (25 per cent), and guarantee options (10 per cent). We also compared the Vaillant flexoTHERM with some of the best outdoor heating systems and heat pumps in the UK in terms of both performance and price.