The Vaillant 40 Litre Stackable Buffer (VP R 40/5 PPS) is a purpose-built accessory for the uniSTOR pure and uniSTOR plus standard diameter cylinder range, designed to be installed either above or below the cylinder as part of a heat pump system. Adding 40 litres of open system volume, this compact buffer provides hydraulic separation, stores additional heating capacity for use at peak demand, and helps de-ice the evaporator without relying on back-up heating – all while adding only 415mm to the overall installed height.
580mm
Outer Diameter, Insulated
3 bar
Max Operating Pressure
85°C
Max Operating Temperature
Stackable Above or Below the Cylinder
The buffer's compact design allows it to sit either above or below a compatible uniSTOR pure or uniSTOR plus standard diameter cylinder, maximising space efficiency without increasing the system's overall footprint.
Standard Diameter Range Only
This 40L buffer (VP R 40/5 PPS) is sized for the uniSTOR pure and uniSTOR plus standard diameter cylinders (150–300L). For the slimline cylinder range, use the 30L buffer (VP R 30/5 SLPPS, 8000011534) instead – the two are not interchangeable due to differing outer diameters.
Hydraulic Decoupling & Peak Demand Support
As well as adding open system volume, the buffer provides hydraulic decoupling between the heat pump and heating circuit, storing heating capacity to smooth out peak demand and supporting evaporator de-icing without requiring back-up electric heating.
Maximises Peak Efficiency
The additional 40 litres of open system volume helps heat pumps run at their peak efficiency, reducing short-cycling and supporting more stable operation.
De-Ices the Evaporator Without Back-Up Heat
Stored heating capacity in the buffer can be used to de-ice the evaporator during defrost cycles, removing the need for an electric back-up heater to perform this function.
Compact Stackable Footprint
Matching the diameter of the standard uniSTOR range and adding only 415mm to the installed height, the buffer is designed to maximise space efficiency within the customer's home.
Low-GWP Insulation
Insulated with polyurethane foam using a low Global Warming Potential propellant (GWP <5), keeping standby energy consumption to under 0.556 kWh per 24 hours.
Steel Construction
The cylinder body and connections are manufactured from steel, sized to handle a maximum operating pressure of 3 bar and a maximum operating temperature of 85°C.
Simple 1-Inch Connections
Water connections are sized at 1 inch diameter, simplifying integration into the wider heat pump and cylinder pipework.
Technical Specification
| Product Identification |
| Product Code |
8000011528 |
| Product Code 2 (Model) |
VP R 40/5 PPS |
| Compatible Cylinder Range |
uniSTOR pure & uniSTOR plus, standard diameter (150–300L) |
| Capacity & Dimensions |
| Nominal Capacity |
40L |
| Outer Diameter, Without Insulation |
450mm |
| Outer Diameter, With Insulation |
580mm |
| Height, Without Insulation |
329mm |
| Height, With Insulation |
415mm |
| Net Weight |
16kg |
| Total Weight (packed) |
56kg |
| Construction & Materials |
| Cylinder & Connection Material |
Steel |
| Heat Insulation Material |
Polyurethane |
| Insulation Propellant GWP |
<5 |
| Water Connection Diameter |
1 inch |
| Operating Parameters |
| Maximum Operating Pressure |
3 bar |
| Maximum Operating Temperature |
85°C |
| Pressure Loss |
2.5 kPa |
| Maximum Volume Flow |
2000 L/h |
| Standby Energy Consumption |
<0.556 kWh/24h |
Frequently Asked Questions
Which cylinders is this buffer compatible with?
The 40L buffer (VP R 40/5 PPS) is designed for the uniSTOR pure and uniSTOR plus standard diameter cylinder range (150 to 300 litres), matching their 580mm insulated outer diameter.
Can this buffer be installed above the cylinder instead of below?
Yes. The buffer is designed to be installed either above or below the cylinder, whichever suits the available space and system layout.
What is the difference between this and the 30L buffer?
The 30L buffer (VP R 30/5 SLPPS, product code 8000011534) is sized for the slimline uniSTOR pure and uniSTOR plus cylinders, with a smaller 490mm insulated diameter. The two are not interchangeable – match the buffer to the correct cylinder range.
What does the buffer do functionally, beyond adding volume?
Beyond the extra 40 litres of open system volume, the buffer provides hydraulic decoupling between the heat pump and heating circuit, stores heat for peak demand periods, and supports evaporator de-icing without needing back-up electric heating.
How much height does the buffer add to the installation?
With insulation fitted, the buffer adds 415mm to the overall installed height when stacked with a compatible cylinder.
