Vaillant hydraulic separator WH 40

Product detailed description

Vaillant WH 40 – hydraulic separator for direct connection under a wall-hung boiler

Vaillant WH 40 (order number 0020248932) is an original hydraulic separator that hydraulically separates the boiler circuit from the heating circuits in multi-circuit systems. This particular version is designed for direct connection under a Vaillant ecoTEC wall-hung condensing boiler (horizontal installation directly beneath the boiler body), without the need for separate wall-mounting brackets – an ideal solution where space in the utility room or boiler room is limited and mounting a standalone separator on the wall would be impractical.

Technical parameters

• Rated flow rate: 3.5 m³/h
• Connection: Rp 1 1/4˝
• Approximate thermal output at 20 K temperature difference: approx. 70 kW
• Approximate thermal output at 11 K temperature difference: approx. 40 kW
• Designed for horizontal installation directly under the boiler
• The package includes a pocket for the temperature sensor, the sensor itself, and complete thermal insulation
• Built-in drain valve for easy draining during servicing
• Mounting and connection material required for installation

Why a hydraulic separator is important

A condensing boiler has its own circulation pump designed precisely for the flow rate and pressure loss corresponding to its heat exchanger. If several separate heating circuits with their own pump groups (for example, a combination of a direct group VDM 10 and a mixing group VDM 20 M) are connected directly to the boiler outlet, hydraulic interactions arise between the individual circuits, which can disrupt the stability of flow through the boiler – especially when thermostatic heads close or mixing valves cycle. The WH 40 solves this problem by physically separating the flow of the primary (boiler) circuit from the flow of the secondary (heating) circuits – both sides exchange heat through a common vessel with minimal hydraulic resistance, but their flows do not affect each other.

When to choose the direct under-boiler mounting variant

The Vaillant WH range of separators is available in several versions – with wall-mounting brackets (for example, variants with catalogue numbers from the 306xxx series) or in this version designed for direct connection under a wall-hung boiler without the need for separate wall fixing. This design is particularly advantageous in:

• Smaller utility rooms or cabinets where there is not enough free wall space to mount a standalone separator
• New buildings, where a compact arrangement of boiler + separator + manifold in a single vertical line is planned from the start
• Renovations, where an older boiler is being replaced with a new ecoTEC and hydraulic separation needs to be added without interfering with the layout of the surrounding pipework

Installation and commissioning

• The WH 40 is mounted directly under the Vaillant ecoTEC wall-hung boiler, onto the flow and return ports with Rp 1 1/4˝ connection
• The temperature sensor is inserted into the supplied pocket and connected to the boiler controller, which adjusts the operation of its own circulation pump based on its reading
• The manifold or the pump groups of the individual heating circuits are then connected to the outlet (secondary) side of the separator
• Once connected, the supplied thermal insulation is fitted, which must cover the entire body including the ports
• The system must be thoroughly vented before commissioning – residual air inside the separator can cause noise and incorrect sensor operation
• The built-in drain valve allows for easy partial draining of the system during future servicing without having to drain the entire water volume

Compatibility

The WH 40 is designed to work with Vaillant ecoTEC plus, ecoTEC pro and ecoTEC exclusive wall-hung condensing boilers (including newer models with IoniDetect technology). Manifolds and pump groups from the VDM series with a 120 mm mounting spacing, or a compatible manifold for 2 or 3 circuits, can be connected to the outlet side. For larger systems with more circuits or higher total building heat loss, where a flow rate of 3.5 m³/h would not be sufficient, we recommend considering a more powerful separator from the WH series – for example, the WH 95 with a flow rate of 8.3 m³/h or the WH 160 with a flow rate of 12 m³/h.

Maintenance

• Check the function of the temperature sensor and its correct connection to the boiler controller once a year
• Check the tightness of the connections, especially after the first heating season
• Check the condition of the thermal insulation and that it is fitted correctly without gaps
• If the system pressure drops, top up water according to the boiler manufacturer's instructions; with harder water, consider installing a softening cartridge
• Use the drain valve for planned servicing or replacement of components in the secondary circuit

Why choose the original Vaillant solution

The original WH 40 separator is hydraulically and mechanically designed precisely to work with Vaillant ecoTEC boilers – flow capacity, pressure losses and connection dimensions all correspond to the manufacturer's specifications, guaranteeing trouble-free operation and optimal system performance. The direct under-boiler mounting variant also saves space and installation time compared to the bracket version designed for standalone wall mounting.

Overview table – Vaillant WH separator range

Choosing the correct separator size depends on the sum of flow rates of all connected heating circuits – undersizing risks increased pressure loss and noise, while significant oversizing results in unnecessarily higher purchase cost without real benefit.

Material design

The WH 40 body is made of high-quality steel or brass casting (depending on the specific design variant), rated for the standard operating pressures and temperatures of heating systems with condensing boilers. The drain valve and connection ports are made of materials resistant to corrosion under normal heating water quality. The supplied thermal insulation made of shaped expanded polypropylene (EPP) reduces heat losses from the separator to the surrounding space and also prevents surface condensation on cooler sections in low-temperature circuits.

Safety and operational reliability

As part of a pressurized hot water system, the WH 40 separator should always be installed in a system equipped with a functional safety valve and a correctly sized expansion vessel. We recommend regularly monitoring the system operating pressure on the boiler display or pressure gauge – a repeated pressure drop may indicate a micro-leak at one of the joints and should be addressed as soon as possible to prevent air from entering the system and the associated problems with water circulation.

Dimensions and space requirements

Thanks to its design for direct mounting under a wall-hung boiler, the WH 40 has a fairly slim, elongated body (approximately 500 mm in length and 114 mm in width including insulation), which fits into the space typically required for mounting a wall-hung boiler, including the clearances required by the manufacturer. This design eliminates the need for additional wall space that would otherwise be taken up by the bracket version of the separator, which is particularly advantageous when installing in smaller utility rooms, alcoves, or attic cabinets.

Effect of the separator on acoustic comfort

In addition to hydraulic separation, the separator also plays an important role in dampening pressure surges and any noise caused by water flow during rapid flow changes (for example, when a thermostatic head suddenly closes). The internal geometry of the WH 40 is designed to dampen these surges and prevent their transmission back towards the boiler, contributing to quieter and smoother operation of the entire system – something especially appreciated by residents of homes where the utility room is close to living spaces.

Relation to boiler output control

The temperature sensor built into the supplied WH 40 pocket provides the boiler controller with information about the temperature in the shared part of the separator, allowing it to more precisely adjust burner output and the operation of its own circulation pump to the current needs of the connected heating circuits. Thanks to this feedback, the boiler does not operate "blindly" based solely on the set heating curve, but also responds to the actual state of the secondary side of the system, contributing to more stable and efficient operation – especially in systems with multiple circuits with different load dynamics (for example, a combination of a fast-responding radiator circuit and a sluggish underfloor heating circuit).

Recommendations for choosing separator size for new projects

When designing a new multi-circuit system, we recommend starting from a preliminary estimate of the total installed boiler output and the number of planned circuits. For typical family houses with a boiler output of up to approx. 25–35 kW and two to three heating circuits, the WH 40 with a flow rate of 3.5 m³/h is generally a sufficient choice. For larger buildings, apartment blocks, or facilities with a higher number of simultaneously operating circuits, we recommend switching to a more powerful WH 95 or WH 160 model, which provide substantial reserve in flow capacity and reduce the risk of future undersizing if the system is expanded.

Frequently asked questions

• What is the difference between this WH 40 version and the bracket version? This version (0020248932) is designed for direct connection under a wall-hung boiler without the need for wall-mounting brackets, while the bracket version is fixed separately to the wall using supplied brackets. The hydraulic parameters (flow rate 3.5 m³/h, connection Rp 1 1/4˝) are the same for both versions.
• Do I also need a separate manifold with the WH 40? Yes, the WH 40 only performs the function of hydraulic separation and does not have a built-in manifold. For a multi-circuit system, a separate manifold or pump groups must be connected to the outlet side according to the number of circuits.
• How do I know if a flow rate of 3.5 m³/h is sufficient for me? We recommend basing this on the sum of flow rates of all connected heating circuits according to the heating project. For larger systems with more circuits, choose a more powerful separator, such as the WH 95 or WH 160.
• Does the separator's filling need to be topped up or replaced regularly? No, the separator does not contain any replaceable filling – it is a passive hydraulic component. Maintenance consists of checking tightness, the sensor, and the condition of the thermal insulation.
• Can the WH 40 be used with boilers other than Vaillant? Hydraulically it is possible with compatible connection dimensions, but we recommend verifying compatibility with a technician, as the WH 40 is primarily designed to work with Vaillant ecoTEC boilers.
• Does installing the WH 40 affect the boiler warranty? Using original Vaillant accessories, installed according to the manufacturer's instructions by an authorized technician, does not affect the boiler warranty – on the contrary, correct hydraulic separation contributes to longer and trouble-free boiler operation.
• What is the warranty on this product? We provide a standard statutory warranty of 2 years from the date of sale for the WH 40 hydraulic separator.

Summary of technical characteristics

The Vaillant WH 40 in the version for direct mounting under a wall-hung boiler represents an efficient and space-saving hydraulic separation solution for medium-sized multi-circuit heating systems. Thanks to its flow capacity of 3.5 m³/h and Rp 1 1/4˝ connection, it covers the needs of most typical family houses with two to three heating circuits, while its compact design without the need for separate wall brackets simplifies installation and saves space in the utility room. Combined with suitable pump groups from the VDM series and a manifold for the required number of circuits, you get a complete, mutually matched solution from a single manufacturer, with guaranteed compatibility of all hydraulic and mechanical parameters throughout the entire system, from the boiler through the separator to the individual pump groups of specific heating circuits.

Additional note on ordering the sensor

The temperature sensor is included as standard in the WH 40 package, and we recommend always connecting it to the boiler controller to maintain full functionality of the hydraulic separation, including the feedback for controlling boiler output according to the current state of the secondary side of the system. Using original Vaillant accessories, installed according to the manufacturer's instructions by an authorized technician, does not affect the warranty on the boiler itself – on the contrary, correct hydraulic separation contributes to its longer and trouble-free operation.