The Vaillant uniSTOR PLUS Heat Pump Cylinder (standard, non-pre-plumbed) is the internal-expansion variant of Vaillant's high-recovery standard cylinder range, available in 150, 175, 210, 250 and 300 litres. Its defining feature is the integrated internal "bubble top" expansion vessel — factory-incorporated within the cylinder body — which eliminates the need for a separate external expansion vessel entirely. The result is a cleaner, more compact installation with fewer connections and a smaller plant room footprint: the preferred choice where space around the cylinder is at a premium.
The installer connects the supplied tundish, three-way motorised valve, unvented cylinder kit and fittings on site to suit the specific layout. Built around Vaillant's large-diameter smooth-bore coil technology, the uniSTOR PLUS delivers standby losses as low as 1.0 kWh/24 h and coil ratings up to 52.5 kW. The 100% recyclable stainless steel inner tank carries a 25-year anti-corrosion guarantee with a 2-year parts and labour warranty on all other components.
Internal
Expansion Vessel Integrated
1.0
kWh/24h min. standby loss
25yr
Anti-Corrosion Guarantee
<5
GWP (Global Warming Potential)
⚠ Installer Requirement
This is an unvented hot water cylinder. Installation, commissioning and servicing must only be carried out by a G3-qualified competent person, in accordance with Building Regulations (England & Wales) Part G and the Benchmark Commissioning Checklist. The internal expansion vessel pre-charge pressure must be verified and adjusted to match system design requirements during commissioning. All installations must be notified to Local Area Building Control or via a Competent Persons Scheme.
⚠ Compatibility & Transport Note
The uniSTOR PLUS standard is designed primarily for use with Vaillant heat pumps (aroTHERM plus, aroTHERM split, flexoTHERM). The 250 L and 300 L models include a secondary return T-piece connection and feature an enlarged coil for compatibility with higher-output ground-source systems. The cylinder must be installed in a dry, permanently frost-free room. Transport and storage must always be vertical — laying the cylinder horizontally may damage the internal expansion vessel.
ℹ PLUS vs PURE — and Standard vs Pre-Plumbed
The uniSTOR PLUS has an integrated internal "bubble top" expansion vessel — no external vessel required, giving the most compact installation footprint. The uniSTOR PURE uses an external expansion vessel (supplied), which allows flexible positioning but occupies more space. This standard (non-pre-plumbed) version supplies the tundish, valve and kit as loose components for on-site connection — ideal where bespoke pipework routing is needed. For a factory-fitted, faster-install option, see the uniSTOR PLUS Pre-Plumbed.
Key Features & Benefits
Integrated Internal Expansion Vessel
The uniSTOR PLUS incorporates a factory-built internal "bubble top" expansion vessel within the cylinder body, completely removing the need for a separate external vessel and its pipe connections. This produces a significantly more compact and tidier installation — fewer components to site, fewer potential leak points, and a smaller overall footprint in the plant room or airing cupboard.
Complete System Kit — On-Site Connection
Supplied with a tundish, three-way motorised valve (28mm), unvented cylinder kit and ¾" × 28mm MI-copper compression fitting for the installer to connect on site. The 250 L and 300 L models also include a secondary return T-piece connection for secondary circulation systems. This standard configuration gives the installer full control over pipework routing.
Large-Diameter Smooth-Bore Coil
Vaillant's smooth-bore coil technology delivers heat exchanger surface areas up to 2.8 m² (300 L) with coil ratings up to 52.5 kW, enabling rapid re-heat and efficient heat transfer from the connected heat pump. The smooth bore actively resists limescale build-up and promotes automatic self-de-scaling, protecting long-term efficiency without chemical additives.
Class-Leading Insulation — from 1.0 kWh/24h
Thermal-injected polyurethane insulation combined with vacuum panels achieves standby losses as low as 1.0 kWh/24 h on the 150 L model — the lowest in class for this cylinder type. Hot water stays at temperature throughout the day, reducing the frequency of heat pump re-heat cycles and cutting running costs for the homeowner.
Factory-Fitted 3 kW Immersion Heater
A 3.0 kW factory-installed immersion heater (13 A, 1.5 mm² cable, 1¼" BSP boss) provides emergency backup heating should the primary heat source be temporarily unavailable for servicing. The adjustable thermostat is set during commissioning and meets G3 unvented cylinder safety requirements.
25-Year Stainless Steel Guarantee
The inner cylinder is made from high-grade 100% recyclable stainless steel with an ultra-hard-wearing outer shell, backed by Vaillant's 25-year anti-corrosion guarantee. All other components carry a 2-year parts and labour warranty, providing one of the most comprehensive coverage packages in the UK cylinder market.
Low GWP & 100% Recyclable
A Global Warming Potential (GWP) of less than 5 and zero ozone depletion from the thermal-injected insulation, combined with a fully recyclable stainless steel tank, makes the uniSTOR PLUS one of the most environmentally responsible cylinders available. Suitable for low-carbon heat pump system specifications and sustainability-focused projects.
Adjustable Feet & Drain Valve
Adjustable levelling feet allow the cylinder to be set plumb on uneven floors without shimming, reducing stress on pipework connections. A pre-fitted drain valve enables safe draining during maintenance or when a property is unoccupied in cold weather, supporting the required annual service regime.
Benchmark Compliant & HWA Member
The uniSTOR PLUS meets EN 12897:2016, carries CE and UKCA marking, and Vaillant is a full member of the Hot Water Association and a licensed Benchmark Scheme member. Suitable for use within MCS-certified heat pump installations supporting BUS (Boiler Upgrade Scheme) grant-funded projects.
Variant Reference — uniSTOR PLUS Standard (Non-Pre-Plumbed)
| Capacity |
Vaillant MPN |
Model Code |
Energy Class |
Outer Diameter (mm) |
| 150 L |
8000012315 |
VIH RW 150/5 B IAES |
B |
595 |
| 175 L |
8000012316 |
VIH RW 175/5 B IAES |
B |
595 |
| 210 L |
8000012317 |
VIH RW 210/5 B IAES |
B |
595 |
| 250 L |
8000012318 |
VIH RW 250/5 C IAES |
C |
595 |
| 300 L |
8000012319 |
VIH RW 300/5 C IAES |
C |
595 |
MPN source: Vaillant installation manual 8000014621-07 (July 2025). IAES = Internal expansion vessel (bubble top), Immersion heater, Stainless steel. Do not confuse with the pre-plumbed PLUS range (MPNs 8000012320–8000012324, suffix PPIAES) or the standard PURE range (MPNs 8000011512–8000011516, suffix ES).
Technical Specifications — uniSTOR PLUS Standard Range
| Specification |
150 L |
175 L |
210 L |
250 L |
300 L |
| Total Tank Capacity (L) |
148.6 |
~175 |
198.4 |
249.2 |
288.7 |
| Hot Water Draw-Off (L) |
127.0 |
~152 |
172.5 |
211.0 |
230.9 |
| Standby Losses (kWh/24h) |
1.0 |
~1.1 |
1.2 |
1.4 |
1.6 |
| Reheat Time 70% (min) |
13.8 |
~14.2 |
14.6 |
10.6 |
7.5 |
| Coil Rating (kW) |
20.8 |
~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 |
| Heat Exchanger Pressure Drop (mbar) |
44 |
~70 |
100 |
170 |
200 |
| Expansion Vessel Type |
Internal "bubble top" — factory-integrated, no external vessel required |
| Max DHW Operating Temp (°C) |
85 |
| Max Heat Circuit Temp (°C) |
95 |
| Immersion Heater Rating (kW) |
3.0 (boss: 1¼" BSP female) |
| Outer Diameter with Insulation (mm) |
595 |
| Cold / Hot Water Connection |
¾" BSP female |
| Net Weight Empty (kg) |
~38 |
~42 |
~46 |
~61 |
~68 |
| Height with Insulation (mm) |
1,000 |
~1,100 |
1,265 |
1,535 |
1,745 |
| Insulation Thickness (mm) |
50 |
| Standard Compliance |
EN 12897:2016 | CE & UKCA Marked | Benchmark Compliant | HWA Member |
* 175 L values are indicative, interpolated from verified 150 L and 210 L data. Height for PLUS standard is the same as the PURE standard equivalent as both share the same cylinder body; the internal expansion vessel is housed within the overall height. Always confirm specifications with the current Vaillant uniSTOR PLUS technical documentation for your specific model before specification.
Frequently Asked Questions
What is the key difference between the uniSTOR PLUS and uniSTOR PURE standard cylinders?
The uniSTOR PLUS has an integrated internal "bubble top" expansion vessel built into the cylinder body, so no separate external expansion vessel is needed — fewer components, fewer connections, smaller footprint. The uniSTOR PURE uses an external expansion vessel (supplied) connected on site, which allows the installer to position it wherever best suits the plant room but requires more space and one additional connection. Both share the same stainless steel cylinder, coil technology, insulation and guarantee terms.
What is supplied in the box, and what does the installer connect on site?
The standard uniSTOR PLUS is supplied with a tundish, 28mm three-way motorised valve, G3 unvented cylinder kit, and ¾" × 28mm MI-copper compression fitting for the installer to connect on site. The 250 L and 300 L models also include a secondary return T-piece connection. The internal expansion vessel, 3.0 kW immersion heater, T&P relief valve and drain valve are all factory-fitted to the cylinder. The installer routes and connects all supplied components to match the specific plant room layout.
Which Vaillant heat pumps is the uniSTOR PLUS standard compatible with?
The uniSTOR PLUS standard is designed to work with Vaillant heat pumps, 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 feature an enlarged coil for compatibility with the higher outputs of ground-source systems. Always use the Vaillant cylinder compatibility matrix to match the cylinder size to the specific heat pump output and system design.
Why choose the standard PLUS over the PLUS Pre-Plumbed?
The standard uniSTOR PLUS is preferred when the installer needs full flexibility over pipework routing — for example, where the pre-plumbed connection positions do not suit the plant room layout, or where a bespoke system design is required. The PLUS Pre-Plumbed is faster to install and better suited to straightforward, standard layouts where saving time on site is the priority.
What guarantee does the standard uniSTOR PLUS 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, including the internal expansion vessel. Full warranty coverage requires installation by a G3-qualified competent person, commissioning in line with the Benchmark Checklist, and annual inspection by a competent person. The completed Benchmark Checklist must be retained by the homeowner.
How do I choose the right capacity uniSTOR PLUS for my property?
As a general guide: 150 L suits 1–2 bedroom homes with one bathroom; 175–210 L suits 3-bedroom homes with 1–2 bathrooms; 250 L suits larger 3–4 bedroom properties; 300 L is recommended for 4+ bedroom homes or properties with higher daily hot-water demand. Always cross-reference with the connected heat pump output and the number of occupants and bathrooms using the Vaillant cylinder compatibility matrix.
