The Vaillant Solar Discharge Vessel (article number 0020145563) is a compact, wall-mounted glycol collection vessel designed for use with Vaillant aroTHERM heat pump systems. Its purpose is straightforward but essential: when a heat pump system's Pressure Relief Valve (PRV) opens, glycol-based antifreeze is discharged from the sealed heating circuit. Without a dedicated collection vessel, this glycol would enter the drainage system — which is environmentally unacceptable and, in most cases, contrary to water regulations.
The Vaillant Solar Discharge Vessel safely captures and retains this glycol discharge, protecting the drainage system and allowing the installer or homeowner to inspect the volume of discharge — a useful indicator of system health. With a 9.7 L usable capacity and a slim wall-mounted profile, it fits neatly in the plant room alongside the heat pump. Where a larger collection capacity is required, multiple vessels can be connected vertically in series. Supplied complete with 2 screws and 2 wall plugs, installation is straightforward.
9.7 L
Collection Capacity
Wall
Mounted — fixings included
Series
Fit vertically for greater capacity
⚠ Compatibility Note
This discharge vessel is specified as an accessory for Vaillant aroTHERM plus and aroTHERM split air-source heat pump systems. It is listed in the Vaillant aroTHERM plus Installer's Quick Guide as the designated discharge vessel for these systems. Always confirm compatibility with the specific system design with reference to the relevant Vaillant installation documentation before fitting. Installation should be carried out by a competent, qualified heating engineer.
ℹ Why a Discharge Vessel Is Needed
Vaillant aroTHERM heat pump systems use a glycol-based antifreeze mix in the sealed heating circuit to prevent freezing in low ambient temperatures. Heat pump circuits are sealed and pressurised; if system pressure exceeds the PRV setting, the valve opens and releases fluid. Because glycol must not be discharged into surface water drainage (it is harmful to aquatic life and regulated under environmental legislation), a dedicated discharge vessel is required to capture and contain it safely. The collected glycol can then be disposed of correctly or the cause of the pressure rise investigated.
Key Features & Benefits
Glycol Capture — Protects Drainage Systems
When the system PRV opens, the discharge vessel safely collects and retains the released glycol antifreeze, preventing it from entering surface water drains or watercourses. This protects the environment, keeps the system compliant with water regulations, and allows the collected discharge to be inspected and disposed of correctly.
9.7 L Capacity — Wall-Mounted Profile
The vessel offers a 9.7 L collection capacity in a compact, wall-mounted body measuring just 305 × 393 × 153 mm. The slim profile minimises the space required in the plant room and sits neatly alongside aroTHERM indoor components. Two screws and two wall plugs are supplied for straightforward secure wall fixing.
Expandable — Vertical Series Connection
Where system design requires a larger total collection capacity, multiple vessels can be connected vertically in series. This provides flexibility for larger aroTHERM installations or systems with higher glycol volumes, without needing a single oversized vessel.
Genuine Vaillant Accessory
Supplied by Vaillant and listed in the official aroTHERM plus Installer's Quick Guide as the designated discharge vessel for these systems. Using a genuine Vaillant accessory ensures correct compatibility and fit, supports system warranty, and confirms the installation meets Vaillant's own design and commissioning standards.
Technical Specifications
| Vaillant Article Number (MPN) |
0020145563 (also referenced as 20145563) |
| EAN |
4024074649695 |
| Collection Capacity |
9.7 litres |
| Width (mm) |
305 |
| Depth (mm) |
393 |
| Height (mm) |
153 |
| Net Weight (kg) |
1.04 |
| Gross Weight inc. Packaging (kg) |
1.24 |
| Mounting |
Wall-mounted (vertical) |
| Series Fitting |
Yes — multiple vessels can be connected vertically in series |
| Supplied With |
Solar discharge vessel, 2 × screws, 2 × wall plugs |
| Compatible Systems |
Vaillant aroTHERM plus, aroTHERM split air-source heat pump systems |
| Function |
Collects heating system glycol on PRV opening — prevents glycol discharge into drainage |
Frequently Asked Questions
What is the Vaillant Solar Discharge Vessel used for?
The vessel is designed to collect glycol antifreeze discharged from a Vaillant aroTHERM heat pump system's Pressure Relief Valve (PRV) when the PRV opens. Because glycol must not enter the surface water drainage system — it is environmentally regulated — this vessel captures the discharged fluid safely. The collected glycol can then be inspected (to help diagnose why the PRV opened) and disposed of responsibly.
Is this vessel mandatory for an aroTHERM heat pump installation?
Yes, in practice. Vaillant lists the discharge vessel (0020145563) in the official aroTHERM plus Installer's Quick Guide as the designated accessory for managing PRV discharge from glycol-filled systems. Environmental regulations in the UK restrict glycol from entering surface water drains, making a collection vessel a practical and regulatory requirement in aroTHERM heat pump installations.
Can the 9.7 L capacity be increased?
Yes. Where a larger collection capacity is required, multiple vessels can be connected vertically in series. This allows installers to size the total discharge capacity to match the glycol volume in the system, without requiring a single large vessel. The slim wall-mounted profile of each unit makes series fitting practical in most plant room configurations.
Why does an aroTHERM heat pump use glycol rather than plain water?
Vaillant aroTHERM heat pumps use a glycol-based antifreeze solution in their sealed heating circuit to prevent the system water from freezing during cold weather operation — including during defrost cycles when the heat pump is actively managing ice formation on the outdoor unit. Glycol also provides corrosion inhibition in the sealed circuit. This is standard practice for air-source heat pump systems operating in UK climates.
Why is glycol not permitted to enter the drainage system?
Ethylene glycol and propylene glycol — both used as antifreeze in heating systems — are harmful to aquatic life if discharged into watercourses, and their disposal into surface water drains is restricted under UK environmental regulations. Heating glycol also typically contains corrosion inhibitors which add further regulated substances. A discharge vessel ensures all released glycol is captured for proper disposal, keeping the installation compliant with both water regulations and environmental legislation.
