The Vaillant uniSTOR PURE Pre-Plumbed Heat Pump Cylinder is a high-recovery, stainless steel unvented hot water cylinder engineered to work in harmony with Vaillant air-source and ground-source heat pumps. Available in 150, 175, 210, 250 and 300 litres, every uniSTOR PURE Pre-Plumbed model arrives with factory-installed pipework, a tundish, a three-way motorised valve and an unvented cylinder kit already fitted — dramatically reducing on-site labour time and removing the risk of incorrect assembly. The external expansion vessel is supplied and connects to the clearly labelled, front-facing connection panel, giving installers maximum flexibility when positioning the vessel to suit the plant room layout.
Built around Vaillant's large-diameter smooth-bore coil technology, the uniSTOR PURE delivers coil ratings from 21.7 kW (150 L) up to 52.5 kW (300 L), maximising heat transfer from the connected heat pump for faster re-heat and consistently high hot-water performance. Thermal-injected polyurethane insulation combined with vacuum panels keeps standby losses as low as 1.8 kWh/24 h, whilst the 100% recyclable stainless steel tank carries a 25-year anti-corrosion guarantee backed by a 2-year parts and labour warranty on all other components.
25yr
Anti-Corrosion Guarantee
<5
GWP (Global Warming Potential)
B
Energy Efficiency Class (A+–F)
85°C
Max DHW Operating Temp
⚠ Installer Requirement
Installation, commissioning and servicing must be carried out by a G3-qualified competent person in accordance with Building Regulations (England & Wales) and the Benchmark Commissioning Checklist. All installations must be notified to Local Area Building Control or via a Competent Persons Scheme. Annual inspection is recommended to maintain safety, efficiency and warranty validity.
⚠ Compatibility & Sizing Note
The uniSTOR PURE Pre-Plumbed range is designed primarily for use with Vaillant heat pumps (aroTHERM plus, aroTHERM split, flexoTHERM). The 250 L and 300 L models feature an increased coil size for compatibility with a wider range of ground-source heat pump systems. Always verify cylinder sizing against the connected heat pump output using the Vaillant compatibility matrix before specification. This cylinder must be installed in a dry, permanently frost-free room and must never be transported horizontally.
ℹ What "Pre-Plumbed" Means
The uniSTOR PURE Pre-Plumbed model ships with the tundish, three-way motorised valve and unvented cylinder kit factory-fitted. The expansion vessel is supplied separately and connects to the external port (the PURE version uses an external expansion vessel — see uniSTOR PLUS for the internal "bubble top" alternative). Labelled, front-facing connections and a mounting plate for controls simplify installation in tight plant rooms and reduce commissioning time.
Key Features & Benefits
Pre-Plumbed Factory Assembly
The tundish, three-way motorised valve and unvented cylinder kit are pre-installed at the factory, saving significant on-site time. Front-facing, clearly labelled connections and a dedicated controls mounting plate ensure a neat, professional installation even in restricted plant rooms.
Large-Diameter Smooth-Bore Coil
Vaillant's smooth-bore coil technology maximises heat exchange surface area (up to 2.8 m² on the 300 L model) for faster re-heat times and quieter operation. The smooth bore design inhibits limescale build-up and promotes automatic de-scaling, protecting long-term efficiency without chemical treatment.
Thermal-Injected PU + Vacuum Insulation
Thermal-injected polyurethane insulation combined with vacuum panels achieves standby losses as low as 1.8 kWh/24 h — among the lowest in class. This superior insulation keeps stored water hot throughout the day, reducing the frequency of re-heat cycles and cutting running costs for the homeowner.
External Expansion Vessel (PURE)
The PURE variant uses an external expansion vessel supplied with the cylinder (12–25 L depending on model). This configuration allows the installer to position the vessel above or below the cylinder to best suit the available space, offering greater flexibility during system design.
Factory-Fitted Immersion Heater
A 3.0 kW factory-fitted immersion heater (13 A, 1.5 mm² cable) provides emergency backup hot water if the primary heat source is temporarily unavailable. The immersion is accessible via a ¾" BSP boss and includes an adjustable thermostat, meeting G3 unvented requirements.
100% Recyclable Stainless Steel Tank
The inner cylinder is manufactured from high-grade 100% recyclable stainless steel with an ultra-hard-wearing outer shell and carries Vaillant's 25-year anti-corrosion guarantee. A 2-year parts and labour warranty covers all other components, making this one of the most comprehensively guaranteed cylinders available.
Low Environmental Impact
uniSTOR PURE cylinders carry a Global Warming Potential (GWP) of less than 5 and zero ozone depletion potential, thanks to the thermal-injected insulation formulation. Combined with the recyclable stainless steel tank, this makes the uniSTOR one of the most environmentally responsible cylinders in its class.
Adjustable Feet & Automatic Air Vent
Adjustable levelling feet simplify installation on uneven floors, while the factory-fitted automatic air vent eliminates the need for a separate manual vent during commissioning. A drain valve is also pre-fitted on the cylinder body, contributing to a clean and complete installation.
MCS-Compatible & Benchmark Compliant
Vaillant is a licensed Benchmark Scheme member and a full member of the Hot Water Association (HWA). The uniSTOR PURE is CE and UKCA marked and meets the requirements of EN 12897:2016. It is compatible with MCS-certified heat pump installations and suitable for BUS (Boiler Upgrade Scheme) grant-funded projects.
Variant Reference — uniSTOR PURE Pre-Plumbed
| Capacity |
Vaillant Article No. (MPN) |
Model Code |
Energy Class |
Diameter (mm) |
Height (mm) |
| 150 L |
8000011517 |
VIH RW 150/5 B ES |
B |
580 |
~1,000 |
| 175 L |
8000011518 |
VIH RW 175/5 B ES |
B |
580 |
~1,265 |
| 210 L |
8000011519 |
VIH RW 210/5 C ES |
C |
580 |
~1,535 |
| 250 L |
8000011520 |
VIH RW 250/5 C ES |
C |
580 |
~1,535 |
| 300 L |
8000011521 |
VIH RW 300/5 C ES |
C |
580 |
~1,745 |
Technical Specifications — Pre-Plumbed PURE Range
| Specification |
150 L |
175 L |
210 L |
250 L |
300 L |
| Total Tank Capacity (L) |
~148 |
~175 |
~210 |
~249 |
~289 |
| Hot Water Draw-Off (L) |
~127 |
~155 |
~173 |
~211 |
~231 |
| Standby Losses (kWh/24h) |
1.8 |
~1.0–1.2 |
1.2 |
1.4 |
1.6 |
| Coil Rating (kW) |
21.7 |
~24 |
26.0 |
40.7 |
52.5 |
| Heat Exchanger Surface (m²) |
1.0 |
~1.2 |
1.4 |
2.4 |
2.8 |
| Primary Flow Rate (L/h) |
900 |
900 |
900 |
900 |
1,300 |
| Max DHW Operating Temp (°C) |
85 |
85 |
85 |
85 |
85 |
| Max Heat Circuit Temp (°C) |
95 |
95 |
95 |
95 |
95 |
| Immersion Heater Rating (kW) |
3.0 |
3.0 |
3.0 |
3.0 |
3.0 |
| Expansion Vessel (L, supplied) |
12 |
12–18 |
18 |
25 |
25 |
| Outer Diameter with Insulation (mm) |
580 |
580 |
580 |
580 |
580 |
| Cold / Hot Water Connection |
¾" BSP female |
¾" BSP female |
¾" BSP female |
¾" BSP female |
¾" BSP female |
| Insulation Thickness (mm) |
40–50 |
50 |
50 |
50 |
50 |
| Standard Compliance |
EN 12897:2016 | CE & UKCA Marked | Benchmark Compliant | HWA Member |
* Approximate values for 175L based on comparable range data. Full specifications for 150L derived from slimline pre-plumbed variant data. Always consult the current Vaillant technical brochure for your specific model before specification.
Frequently Asked Questions
What is the difference between the uniSTOR PURE and uniSTOR PLUS?
The key difference is the expansion vessel arrangement. The uniSTOR PURE uses an external expansion vessel that is supplied with the cylinder and connected to the externally accessible port — offering flexibility in vessel positioning. The uniSTOR PLUS incorporates an internal "bubble top" expansion vessel, which creates a neater and more compact installation particularly suited to tight plant rooms or airing cupboards. Both are available in pre-plumbed and standard (non-pre-plumbed) variants and share the same core stainless steel cylinder, coil technology and guarantee terms.
What does pre-plumbed mean, and what comes already fitted?
Pre-plumbed means the cylinder ships with key components factory-installed to save installation time and reduce on-site errors. On the uniSTOR PURE Pre-Plumbed, the following are pre-fitted: the tundish, three-way motorised valve, unvented cylinder kit, and all labelled front-facing pipe connections. The expansion vessel is supplied separately for external connection. A mounting plate for heat pump controls is also included.
Which Vaillant heat pumps is the uniSTOR PURE Pre-Plumbed compatible with?
The uniSTOR PURE Pre-Plumbed is designed to work with the full Vaillant domestic heat pump range, including the aroTHERM plus (3.5–12 kW), aroTHERM split (3.5–12 kW), and flexoTHERM ground-source heat pump (5–19 kW). The 250 L and 300 L models have an enlarged coil specifically to support the higher output of ground-source heat pump systems. Consult the Vaillant cylinder compatibility matrix to match the correct cylinder capacity to the heat pump output.
Is the uniSTOR PURE Pre-Plumbed eligible for the Boiler Upgrade Scheme (BUS) grant?
The Boiler Upgrade Scheme grant is awarded for the installation of a qualifying heat pump, not the cylinder itself. However, the uniSTOR PURE Pre-Plumbed is compatible with Vaillant MCS-certified heat pumps used in BUS grant applications. The cylinder must be installed as part of a complete, G3-compliant unvented system by a qualified installer. Always verify BUS eligibility requirements with the Ofgem guidance current at the time of application.
What guarantee does the uniSTOR PURE Pre-Plumbed carry?
Vaillant provides a 25-year anti-corrosion guarantee on the stainless steel inner tank and a 2-year parts and labour warranty on all other components. To maintain the full warranty, the cylinder must be installed by a competent, G3-qualified person, commissioned in accordance with the Benchmark Checklist, and serviced annually. The Benchmark Checklist must be completed and signed at commissioning and retained by the homeowner.
Which capacity uniSTOR PURE Pre-Plumbed should I choose?
As a general guide: 150 L suits 1–2 bedroom homes with 1 bathroom; 175–210 L is suitable for 3-bedroom homes with 1–2 bathrooms; 250 L suits larger 3–4 bedroom properties; and 300 L is recommended for properties with 4+ bedrooms, multiple bathrooms or higher hot-water demand. Always use the Vaillant compatibility matrix alongside your specific heat pump model to confirm the optimum cylinder size for your project.
