Vaillant heat pumps: aroTHERM range and cylinders

Vaillant sells air source heat pumps in the UK under the aroTHERM name, in outputs from 3.5kW to 12kW, alongside ground source units and hot water cylinders. The aroTHERM plus range is available in 3.5kW, 5kW, 7kW, 10kW and 12kW outputs, which the certification listing for the scheme that approves innovative heating measures records in the same five steps¹. The aroTHERM Split is offered in the same five outputs and is described as delivering heating and hot water comfort for a wide range of properties, making it suitable for most UK homes³.

For a household weighing energy independence, an air source heat pump moves space heating and hot water off gas and onto electricity, which removes the gas supplier and the gas grid from the equation but leaves the electricity grid, an electricity supplier and the manufacturer's controls ecosystem in place. Vaillant's own system design assumes that chain: an outdoor heat pump unit installed close to the home, along with a cylinder, a control and a wiring centre¹.

The aroTHERM range and the wider Vaillant portfolio

The aroTHERM plus is the established air source model, and the aroTHERM pro was launched in 2026 alongside the first-generation plus, with the plus itself refreshed in 2026 to add a Flexible Space Function, a new anthracite finish and lower noise levels⁷. The aroTHERM Split sits in the same family and shares the five output steps³.

Vaillant also makes ground source equipment. The flexoTHERM exclusive ground source heat pump is Quiet Mark certified in its 5kW, 8kW and 15kW 400V models⁹. That matters for households with the land or a borehole available, since a ground source unit draws heat from the ground rather than the air and is not exposed to the same outdoor air temperatures, though the installation cost and groundworks are a different proposition from an air source unit.

The hot water side is not an afterthought. The aroTHERM plus is stated to provide up to 25% more usable hot water, a figure that appears in both the Quiet Mark listing and the aroTHERM plus product page². In practice that figure depends on the cylinder it is paired with and on how the system is set up, so it is a maker's claim about the combination rather than a property of the outdoor unit alone.

Cold weather performance: tested down to -25°C

Vaillant states that it has tested the heat pump in extreme conditions of up to -25°C, so a householder does not need to worry about performance during cold spells¹. The company's servicing guidance repeats the point more generally: all Vaillant heat pumps have been tried and tested in adverse weather conditions including minus temperatures⁶.

Independent guidance sits in a similar place but with a caveat about output rather than operation. The Energy Saving Trust states that heat pumps can perform down to -15°C or lower, but notes there may come a point when the heat pump's output is not enough for the home¹¹. That distinction matters: a unit continuing to run at -25°C is not the same as a unit meeting the full design heat loss of the house at that temperature. The Energy Saving Trust's fact check page puts most current models as working fine down to about -25°C, with some advanced cold-climate heat pumps working in temperatures as low as -35°C¹².

The practical consequence is that cold weather performance is a design question as much as a product question. A system sized on a proper heat loss calculation, with emitters able to deliver the required output at a lower flow temperature, will hold its indoor temperature through a cold snap. A system sized tightly or paired with undersized radiators may not, whatever the outdoor unit is rated to. More on this is at heat pumps in cold weather and heat pump sizing.

Noise: 32dB and Quiet Mark accreditation

Vaillant states that the entire range of aroTHERM plus and aroTHERM pro heat pumps has been certified by Quiet Mark¹. The aroTHERM Split is listed as a Quiet Mark certified product³, and the flexoTHERM exclusive ground source models carry the same certification in their 5kW, 8kW and 15kW 400V versions⁹.

Noise is not only a comfort question. Planning rules in England and Wales use a noise assessment for air source heat pumps, and the MCS 020 calculator applies a pass or fail noise limit of 37.0 dB(A) for a two heat pump assessment¹³. That is the threshold against which a proposed installation is judged, and it is a fixed number rather than a range. A unit that is quiet at source makes that assessment easier to pass, particularly where the outdoor unit has to sit close to a neighbouring boundary.

The wider context is that heat pump noise is measured and regulated in a way gas boiler noise is not, because the outdoor unit sits outside the building envelope. Where a unit can be sited, and what clearances it needs, are covered at where a heat pump outdoor unit can go and how noisy is a heat pump.

Smart controls and the myVAILLANT ecosystem

Vaillant's controls chain runs through the myVAILLANT app. The app allows users to adjust the temperature through simple voice commands with Amazon Alexa and Apple HomeKit, and the myVAILLANT connect internet gateway monitors the health of the heat pump, sending a notification through the app if an error occurs¹⁴.

That gateway is the point of dependence. Remote control, health monitoring and voice control all run through a home broadband connection, Vaillant's servers and a manufacturer's app. Local control at the appliance and at the wired control continues without an internet connection, but scheduling from away and remote diagnostics do not. A household that wants to keep heating running through a broadband outage can, but loses the remote layer.

The system itself is assembled from several parts: an outdoor heat pump unit, a cylinder, a control and a wiring centre¹. Each of those components must be registered with Vaillant as part of the system to ensure proper guarantee coverage, which means the controls and cylinder are not incidental to the warranty position¹. Controls, weather compensation and smart operation more generally are covered at heat pump controls.

Warranty: 2 years as standard, 7 with conditions

Vaillant states that guarantees of up to 10 years are available on gas boilers and 7 years for heat pumps through a Vaillant Advance installer¹⁵. The heat pump guarantee terms set the registration deadline at 30 days from installation, providing the full 28-digit serial number⁴. Failure to register within that period results in the guarantee reverting to 12 months from the date of installation, provided the Benchmark logbook has been completed, or otherwise 12 months from the date of manufacture⁴.

Cylinders carry their own, shorter term. Vaillant guarantees the domestic hot water cylinder for 2 years from the date of installation against manufacturing defects, with registration made on the myVAILLANT web portal or through the installer⁵. Cylinder faults within the guarantee period go to Vaillant UK Service on 0330 100 3143⁵.

Out of guarantee, the repair terms are narrower than the original cover. Vaillant states that all parts fitted are guaranteed for 12 months and all labour is covered for 90 days¹⁶. Spare parts used as part of a service under the guarantee are guaranteed for 12 months against defective material or faulty workmanship, replaced free of charge, and that does not extend the original guarantee term⁴.

Cost, servicing and expected lifespan

Vaillant states that a heat pump service starts from £250 including VAT, and that this includes all labour charges, with additional charges if replacement parts are required⁶. The service interval is once a year after the initial installation⁶. Annual servicing is necessary to maintain the heat pump and system product guarantees, and can be performed by the Vaillant Service team¹. The guarantee terms add the alternative: servicing by the Vaillant Service organisation or another suitably competent engineer with valid qualifications and certification⁴.

On lifespan, the maker and the independent bodies differ in a way that favours the householder. Vaillant states that with regular servicing, a well designed and installed heat pump should last over 15 years⁶. The Energy Saving Trust goes further, stating that the heat pump itself is likely to last 20 years or more, longer than the average gas or oil boiler¹⁷. The CPA gives a lifespan of 20+ years¹⁸. The gap between the maker's figure and the independent ones is not a dispute about the equipment so much as about conditions: the maker's number is tied to servicing and to the quality of the original design and installation.

There is no published Vaillant list price for a supplied and fitted heat pump in the material here, so installation prices are installer-quoted. Servicing is the one figure with a published starting point, and it is a recurring cost rather than a one-off. Servicing and maintenance more broadly is covered at heat pump servicing and maintenance.

Fault codes, water pressure and contacting Vaillant

Fault codes display on the appliance interface, normally located within the property, and Vaillant notes that resetting the heat pump using the round reset button can often resolve a fault or temporarily get it working again¹⁰. F.22 means low water pressure in the system, and Vaillant gives the normal range as 1 to 1.5 bar¹⁰.

Other codes point at sensors and wiring rather than pressure. F.774 is an air inlet temperature sensor fault, from a fault in the electrical connection for that sensor. F.514 is a compressor inlet temperature sensor fault, from a fault in the electrical connection or a defective sensor. F.520 is a building circuit flow temperature sensor fault, with the same two possible causes. F.42 is a coding resistor fault, with possible causes being a damaged or unset coding resistor or damage to the coding resistor wiring harness. F.103 is a fault with a spare part identified, with possible causes being incorrect software or an incorrect printed circuit board fitted, and it requires a Vaillant engineer¹⁰.

Contact runs through Vaillant Group Service on 0330 100 3540⁴. For a heat pump in guarantee, call that number and select option 1; for an out-of-guarantee repair, select option 2 to book an appointment¹⁶. The out-of-guarantee repair service is suitable for heat pumps that are no longer within their manufacturer's guarantee¹⁶.

Water quality is a guarantee condition as well as a performance one. Vaillant requires that the system has been flushed prior to the heat pump installation to ensure it contains no contaminants, that the water is checked for hardness and salinity and correctly inhibited before installation, that it is maintained clean and inhibited throughout the heat pump's life cycle, and that adequate frost protection is in place, such as glycol or anti-frost valves⁴.

Vaillant as a company: engineering, UK manufacturing and reputation

Vaillant's UK manufacturing is described as award winning, combined with proven German engineering¹⁹. That combination is the company's own positioning, and it matters for a household in two ways: the engineering base is European, and the assembly and support base is British, which shortens the supply chain for parts and service.

The brand appears in independent comparisons rather than only in its own material. Which? lists Scottish Power among heat pump offers that include Daikin, Vaillant and Mitsubishi heat pumps with two years of annual servicing from Domestic & General²⁰. That is a third-party arrangement rather than a Vaillant warranty term, and it shows the brand being selected by an energy supplier and a servicing provider as one of a small set of manufacturers they will work with.

For independence, the company position is a dependence like any other. A Vaillant heat pump keeps a household tied to Vaillant for fault codes, in-guarantee repairs and the controls ecosystem, and to a Vaillant Advance installer for the longest guarantee term. The fuel dependence changes from gas to electricity; the manufacturer dependence does not disappear. Alternatives from other makers are covered at Viessmann Vitocal heat pumps and Grant Aerona 290 heat pump.

Finding an installer and the Boiler Upgrade Scheme

The Boiler Upgrade Scheme provides grants for heat pump installations across England and Wales²¹. Air-to-water heat pumps are an eligible technology under the scheme²², and ground source heat pumps are also eligible²³. The scheme provides upfront capital grants to support the installation of heat pumps and biomass boilers in homes and non-domestic buildings²⁴. Vaillant directs householders to their installer for confirmation of whether they qualify¹⁵.

The application is installer-led and a property owner cannot apply directly²⁵. The process runs in order: contact suitable MCS certified installers to get quotes for the work, confirm eligibility, agree a quote with the chosen installer, and the installer applies on the householder's behalf on the Ofgem website²⁶. Installers are the ones who apply for the grant on behalf of their customers²⁷, and the recommendation is to contact at least three installers to obtain quotes²⁸. Ofgem administers the scheme, and the installer applies through it²⁹.

The scheme has been expanded: an additional £1.5 billion was announced for it, which the certification body states will help install another 200,000 heat pump installations³². The purpose is aimed at reducing the cost of installing a heat pump, and consumers are advised to check their eligibility for available government grants³³. Wider grant and funding routes across the four nations are covered at heat pump grants and how much does a heat pump cost with a Boiler Upgrade Scheme grant.