uniSTOR plus VIH RW 400

Product detailed description

Vaillant uniSTOR plus VIH RW 400 hot water storage tank

Vaillant uniSTOR plus VIH RW 400 is a stationary, indirectly heated hot water storage tank with a volume of 375 liters, designed to work in conjunction with a heat pump as the sole heat source. Within the uniSTOR plus range, it is the larger model, suitable for households with four or more members or for buildings with higher and uneven demand for hot water, for example, houses with two or more bathrooms. Compared to smaller models in the range, the tank has a wider and shorter shape, which allows it to be placed even in rooms with a lower ceiling.

The inner tank is made of steel with a high-quality glazed surface (enamel), which ensures long-term resistance to corrosion on the potable water side. A magnesium protective anode is included in the delivery, which actively protects the interior of the tank throughout the product's lifetime. The tank is equipped with one heating heat exchanger with a smooth tube, optimized for cooperation with the lower output temperatures of the heat pump.

Technical parameters of VIH RW 400

• Tank volume: 375 liters
• Tank height (with casing): 1502 mm
• Width (with casing): 790 mm
• Depth (with casing): 900 mm
• Empty tank weight (without water): approximately 181 kg
• Operating weight of the filled tank: approximately 556 kg
• Maximum operating pressure (domestic water): 10 bar
• Maximum operating pressure (heating circuit): 10 bar
• Maximum hot water temperature: 85 °C
• Built-in magnesium protective anode against corrosion
• Glazed inner tank surface (enamel)
• One heating heat exchanger with a smooth tube for connection to a heat pump

Construction and thermal insulation

Thanks to its wider diameter (790 mm) and lower height (1502 mm) compared to the RW 300 model, the RW 400 tank is also suitable for rooms with a lower ceiling, where a taller tank could not be placed. The casing is insulated with rigid PU foam applied directly to the steel tank, which eliminates thermal bridges and reduces standby losses. The volume of 375 liters provides a significant reserve of hot water, which is able to cover simultaneous consumption from multiple bathrooms or short-term higher consumption during visits.

Due to the higher weight of the filled tank (556 kg), attention must be paid to the floor load-bearing capacity when designing the installation, especially in the case of installation outside the ground floor. In the vast majority of family homes with a concrete or masonry floor, this is not a problem, but for wooden ceiling structures, we recommend a structural assessment by a statics engineer.

Installation and connection

The tank is installed as a free-standing unit on adjustable legs. Connections for hot and cold water, circulation, and the heating circuit are solved with standard threaded connections at the top of the tank. Due to the diameter of 790 mm, it is necessary to plan sufficient floor space in the technical room – we recommend a minimum of 100 × 100 cm including the working space around the tank for access to the inspection opening and the anode.

The tank is compatible with Vaillant heat pump controls (senzoCOMFORT, multiMATIC), which allow setting heating time programs, priority for hot water preparation, and periodic anti-legionella cycles. When installing in larger households with multiple draw-off points, we recommend adding a circulation pump with a time-controlled system, which ensures quick availability of hot water even at more distant draw-off points.

Compatible accessories

It is possible to add a connection kit with a safety valve for the domestic water side, an expansion vessel for hot water, insulation sleeves for the connecting pipes, and a temperature sensor for the tank compatible with the heat pump control unit to the VIH RW 400 tank. For larger buildings, we also recommend a circulation pump with thermally insulated circulation piping, which reduces heat losses along the route to the individual draw-off points.

For whom is the RW 400 model suitable

The RW 400 model is suitable for a household of 4–6 people, a house with two bathrooms, or a building with higher demands for hot water comfort. Thanks to its 375-liter volume, it is able to cover short-term increased consumption, for example, during weekends with guests or simultaneous showering by multiple people.

Frequently asked questions (FAQ)

Why is the RW 400 tank shorter than the RW 300, even though it has a larger volume?
Vaillant increases the diameter of the tank instead of its height for models from 400 liters upwards, resulting in a wider and shorter tank shape, suitable even for rooms with a lower ceiling.

How much space do I need for installation?
We recommend planning for a minimum floor space of 100 × 100 cm and a minimum room height of 1700 mm including working space.

Will a standard floor support 556 kg of a filled tank?
Yes, in masonry buildings with a concrete floor, but for wooden structures, we recommend consulting a statics engineer before installation.

Is the RW 400 tank suitable for a house with two bathrooms?
Yes, the 375-liter volume is sufficient to cover simultaneous consumption from two bathrooms without a significant drop in temperature comfort.

How often should the magnesium anode be checked?
We recommend a visual inspection once a year, more frequently in areas with hard water, as part of the regular service inspection of the heat pump.

Operation with a heat pump

Heat pumps achieve the highest efficiency at lower output temperatures of the heating water (typically 35–55 °C), unlike gas boilers, which usually deliver water at 70–80 °C. The VIH RW 400 tank is directly shaped by this fact – a larger volume in combination with an efficient heat exchanger allows sufficient hot water to be prepared even at a lower temperature gradient of the heat pump, which reduces the number of compressor switching cycles and extends its lifespan. When designing the performance of the heat pump for a 375-liter volume, we recommend consulting a designer who will consider the real consumption profile in the household.

Maintenance and service

Regular maintenance consists of checking and, if necessary, replacing the magnesium anode, checking the functionality of the safety valve on the domestic water side, and occasional descaling of the tank, especially in areas with hard water. Access to the inspection opening and the anode is from the front side of the casing, which allows service directly on site without the need to disconnect the tank from the distribution. We recommend performing the service at least once a year, ideally together with the annual service inspection of the heat pump.

Comparison within the uniSTOR plus range

The RW 400 model follows the smaller RW 250 and RW 300 models and precedes the largest RW 500 model. If your household regularly experiences high simultaneous hot water consumption in multiple bathrooms or you operate a building with higher comfort requirements (for example, a guesthouse or a larger family home), we recommend also considering the largest RW 500 model with an even higher hot water reserve.

Economic and ecological benefits

In combination with a heat pump that uses renewable energy from the surrounding environment, the VIH RW 400 tank represents a significantly more cost-effective solution for heating hot water compared to a classic electric water heater or on-demand heating. The high-quality PU insulation minimizes heat losses between individual withdrawals, which directly translates into lower operating costs for the household, especially with regular and higher daily consumption typical of larger households.

Operational safety

The VIH RW 400 tank is dimensioned for a maximum operating pressure of 10 bar on both the domestic water and heating water sides, which covers the requirements of standard household water supply systems. In every installation, it is essential to install a certified safety valve on the hot water side with an opening pressure according to current regulations, which protects the tank from overpressure caused by thermal expansion of water during heating. We also recommend adding an expansion vessel on the hot water side – with a volume of 375 liters, the volume of thermal expansion of water during heating is in the tens of liters, so a properly dimensioned expansion vessel significantly reduces the frequency of the safety valve opening.

When choosing the installation location, we also recommend considering the possibility of draining any water leaking from the safety valve (e.g., into a floor drain or through a drain pan), since with tanks of this size, the amount of water leaking in case of a failure may be greater than with smaller tanks.