Vaillant
The Vaillant aroTHERM_VWL55_Operating_Instructions is a monobloc air-source heat pump available in 5.5kW and 8.5kW outputs, using R410A refrigerant and requiring a 230V single-phase connection.
The Vaillant aroTHERM_VWL55_Operating_Instructions covers the 5.5kW and 8.5kW monobloc air-source heat pumps. These units utilize R410A refrigerant and require a 230V single-phase electrical supply. This technical guide details the VWL 55/3 A and VWL 85/3 A variants, including hydraulic requirements of 0.5 bar minimum pressure and compatibility with the VWZ AI control interface. It serves as a reference for engineers regarding fault codes, service intervals, and system maintenance.
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Full technical specifications extracted from the manufacturer brochure. Empty sections are hidden.
The Vaillant aroTHERM range, specifically the VWL 55/3 and VWL 85/3 models, represents a monobloc air-source heat pump solution engineered for the UK domestic market. These units are self-contained, meaning the entire refrigerant circuit is housed within the outdoor unit, simplifying installation by requiring only hydraulic connections to the indoor system. The VWL 55/3 provides a nominal output of approximately 5.5kW, while the VWL 85/3 delivers 8.5kW, making them suitable for a variety of property sizes from well-insulated flats to medium-sized semi-detached homes.
Both models utilize R410A refrigerant, which has a Global Warming Potential (GWP) of 2088. As monobloc units, they operate on a standard 230V single-phase power supply. For hydraulic integration, the system requires a minimum operating pressure of 0.5 bar. It is compatible with unvented domestic hot water cylinders and can be controlled via the VWZ AI heat pump control interface module or a dedicated weather compensator to optimize efficiency based on outdoor ambient temperatures.
Maintenance and longevity are supported by a mandatory 12-month service interval. Engineers must perform annual inspections, including checking system pressure and ensuring the external evaporator fins are clear of debris such as leaves or branches. Because these units contain fluorinated greenhouse gases, F-Gas certification is required for certain maintenance tasks, particularly those involving the refrigerant circuit.
The diagnostic system uses a digital display to communicate operational status and faults. Common issues include Fault 01/3 or code 42, which typically indicate a problem with the coding resistor. The F.XXX prefix denotes a specific internal fault that requires investigation by a competent person. A dedicated reset button is provided to clear temporary lockouts once the underlying cause has been addressed.
During operation, users may observe steam escaping from the unit or hear bubbling and whistling noises. These are documented as normal characteristics of the thawing procedure and refrigerant flow, rather than mechanical failures. For homeowners, the casing should be cleaned only with a damp cloth and mild soap to avoid damaging the control elements or the protective finish of the outdoor housing.
Every fault code listed in the manufacturer brochure, with likely causes and engineer actions. Each code has a permalink — paste a URL like https://www.boilertag.com/heat-pumps/vaillant/arotherm-vwl55-operating-instructions#fault-fault 01/3 to jump straight to the entry.
| Code | Meaning | Details |
|---|---|---|
| Fault 01/3 | Coding resistor Show causes & actionsFault message shown on display Likely causes
User action Contact a competent person. | Details |
| 42 | Coding resistor Show causes & actionsSpecific fault number shown on display Likely causes
User action Contact a competent person. | Details |
| F.XXX | Fault in the heat pump Show causes & actionsAppears instead of the basic display; a plain text display explains the displayed fault code. User action Contact a competent person. Reset procedure The reset button is used to reset the heat pump faults and heat pump accessory faults. | Details |
| The product no longer works. | Power supply disconnected Show causes & actionsLikely causes
User action Ensure that there has not been a power cut and that the product is correctly connected to the power supply. When the power supply is re-established, the product automatically starts up. If a fault is still present, contact your competent person. | Details |
| Noises (hissing, knocking, humming) | Normal operating noises Show causes & actionsThese noises do not constitute a fault with the heat pump. Likely causes
User action None required. These noises are normal during various operating modes (Start, Thawing, Stop). | Details |
| The product releases steam. | Thawing procedure Show causes & actionsIn winter and during the thawing procedure, steam may escape from the product. Likely causes
User action None required. This is a normal part of the thawing process. | Details |
Patterns that group across the manufacturer's fault-code table. Each entry links to the full code listing further down the page.
User: Contact a competent person.
Triggered by fault code Fault 01/3.
User: Contact a competent person.
Triggered by fault code F.XXX.
User: Ensure that there has not been a power cut and that the product is correctly connected to the power supply. When the power supply is re-established, the product automatically starts up. If a fault is still present, contact your competent person.
Triggered by fault code The product no longer works..
User: None required. These noises are normal during various operating modes (Start, Thawing, Stop).
Triggered by fault code Noises (hissing, knocking, humming).
Common questions from engineers and homeowners about the Vaillant aroTHERM.
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Specifications on this page are extracted from the manufacturer brochure. Always cross-check against the latest datasheet before commissioning or quoting. Last updated 30 April 2026.
User: None required. This is a normal part of the thawing process.
Triggered by fault code The product releases steam..