Vaillant dual-circuit distributor with hydraulic separator WHV 35

Product detailed description

Vaillant WHV 35 – dual-circuit distributor with built-in hydraulic separator

Vaillant WHV 35 (order number 0020042429) is an original dual-circuit distributor with a built-in hydraulic separator, colloquially also known as a "low-loss header". It is a key component for multi-circuit heating systems built on Vaillant ecoTEC plus, ecoTEC pro and ecoTEC exclusive condensing boilers, combining two functions in one compact, thermally insulated body – hydraulic separation of the boiler circuit from the heating circuits, and distribution of water into two separate branches, to which pump groups from the VDM series (both direct and mixing) are then connected.

What exactly is included in the package

• Distributor body with built-in hydraulic separator for two separate circuits
• Separator sensor (temperature sensor of the common return/supply branch for boiler control purposes)
• Mounting brackets for fixing to a wall or boiler room frame
• Complete thermal insulation made of moulded EPP
• Mounting spacing of 120 mm for connecting VDM series pump groups

What is a hydraulic separator (low-loss header) and why is it needed

A condensing boiler has its own internal circulation pump designed for a specific flow rate and pressure loss, which the manufacturer takes into account when designing the heat exchanger and burner. If several separate heating circuits with their own circulation pumps (for example a radiator circuit via VDM 10 and underfloor heating via VDM 20 M) were connected directly to the boiler outlet, they would mutually affect each other hydraulically – changes in flow on the heating side (for example thermostatic heads closing or a mixing valve cycling) would be transmitted back to the boiler circuit and could disrupt the boiler's correct operation, or cause unwanted cycling.

The hydraulic separator (low-loss header) solves this problem by physically decoupling the flow of the boiler circuit from the flow of the heating circuits – both sides are connected only through a common vessel with low hydraulic resistance, so they can "exchange" heat without affecting each other's flow and pressure. Vaillant WHV 35 integrates this function directly into the body of the dual-circuit distributor, saving space in the plant room and simplifying installation compared to a separate low-loss header and a separate distributor.

Dual-circuit solution in one body

In addition to hydraulic separation, the WHV 35 also serves as a distributor for two separate heating circuits with a connection spacing of 120 mm – this spacing allows direct mounting of VDM series pump groups (direct VDM 10 or mixing VDM 20 M / VDM 25 M), depending on the temperature control required by the given circuit. A typical arrangement is a combination of one direct group for a radiator circuit and one mixing group for underfloor heating, but it is equally possible to connect two mixing groups for two independently controlled low-temperature circuits (for example two underfloor heating zones with different temperature requirements).

Installation and connection

• The WHV 35 is mounted on the wall of the plant room using the supplied mounting brackets, usually near the boiler
• The supply and return pipes from the boiler are connected to the inlet side of the separator
• Pump groups of the individual circuits are connected to the outlet side with 120 mm spacing
• The separator sensor is connected to the boiler controller, which uses its value to adjust the output and operation of the boiler's circulation pump according to the current needs of the connected circuits
• After connection, the thermal insulation is fitted, which must cover the entire body including the connection ports
• The system must be thoroughly vented, as air trapped inside the separator can cause incorrect sensor operation as well as system noise

When to choose the WHV 35 instead of a separate low-loss header and distributor

The 2-in-1 solution (distributor + low-loss header in one body) is particularly suitable for systems with exactly two heating circuits, where no further expansion is planned in the future – it saves space, simplifies installation and reduces the number of joints (and thus potential leak points) compared to a combination of a separate distributor (e.g. 307556 for 2 circuits) and a separate low-loss header (e.g. WH 40). For systems with more than two circuits, or where future expansion is uncertain, it is more suitable to choose a separate, larger low-loss header (for example WH 95 or WH 160) combined with a distributor for the required number of circuits, which can more easily be supplemented with additional pump groups.

Compatibility

The WHV 35 is designed to work with Vaillant ecoTEC plus, ecoTEC pro and ecoTEC exclusive condensing boilers (including newer models with IoniDetect) and VDM series pump groups (VDM 10 direct, VDM 20 M and VDM 25 M mixing). The 120 mm spacing ensures compatibility across the entire Vaillant pump group range, so direct and mixing circuits can be freely combined according to the current needs of the heating system.

Maintenance

• Check the functionality of the separator sensor and its correct connection to the boiler controller once a year
• Verify the tightness of screw connections, especially after the first heating season, when thermal expansion of the material occurs
• Check the condition and fixing of the thermal insulation, which should cover the entire body without gaps
• If the system pressure drops, top up water according to the boiler manufacturer's instructions; in case of hard water, consider installing a softening cartridge
• If deposits or clogging of the internal space of the separator are suspected (e.g. in systems after many years of operation without water treatment), it is advisable to have the check carried out by an authorised service technician

Why choose an original Vaillant solution

The compact dual-circuit WHV 35 solution is designed specifically to work with Vaillant boilers and pump groups, including hydraulic parameters (pressure losses, flow characteristics) as well as mechanical compatibility (120 mm spacing, type of screw connection). Integrating the low-loss header directly into the distributor body reduces the number of components, joints and installation time compared to a combination of separate parts, which also translates into a lower risk of leaks in the future.

Step-by-step design procedure for a multi-circuit system with the WHV 35

When designing a heating system with the WHV 35 dual-circuit distributor, we recommend following several steps to ensure trouble-free operation of the entire system:

• 1. Determine the number and type of circuits – find out how many separate heating circuits the system will contain and what temperature control each requires (same temperature as the boiler, or a lower controlled temperature).
• 2. Choose the pump groups – for a circuit with the same temperature, choose the direct VDM 10 group; for a circuit with a lower controlled temperature, choose the mixing VDM 20 M or VDM 25 M group according to the required flow rate.
• 3. Install the WHV 35 – mount the body on the wall near the boiler using the supplied brackets and connect the supply and return pipes from the boiler.
• 4. Connect the pump groups – connect the chosen pump groups for the individual circuits to the outlet side with 120 mm spacing.
• 5. Electrical connection and control setup – connect the separator sensor to the boiler controller and the mixing valve actuators to the respective controllers of the individual circuits.
• 6. Filling, venting and test operation – fill the system with water, vent it thoroughly and verify the correct operation of the control system on all connected circuits before handing over to the customer.

Operational safety

Like any heating system component working with hot water under pressure, the WHV 35 should be part of a system equipped with a functional safety valve and an expansion vessel sized for the total volume of the system including all connected circuits. We also recommend regularly checking the system's operating pressure on the boiler's pressure gauge, and in case of repeated pressure drops, finding and eliminating the cause (most often micro-leaks in joints or fittings), as long-term operation at low pressure can cause air to enter the system and subsequent problems with water circulation and the function of the separator.

Frequently asked questions

• How many circuits is the WHV 35 designed for? The WHV 35 is a dual-circuit distributor with a built-in low-loss header – exactly two pump groups (direct or mixing) can be connected to it, depending on the needs of the given system.
• Can I connect two mixing groups at once to the WHV 35? Yes, any combination of direct and mixing groups from the VDM series can be connected according to the needs of the individual circuits – for example two mixing groups for two independently controlled underfloor heating zones.
• What does the separator sensor do? The sensor measures the temperature in the common part of the separator and sends this value to the boiler controller, which uses it to adjust the output and operation of the boiler's own circulation pump.
• Can the WHV 35 be expanded with a third circuit in the future? No, the WHV 35 has a fixed number of two outlets. If expansion to more circuits is planned, we recommend choosing a separate low-loss header with sufficient flow capacity (e.g. WH 95) combined with a distributor for the required number of circuits.
• Is any additional water treatment or filtration required? We recommend following the general quality principles for filling and top-up water according to the boiler manufacturer's instructions, and possibly adding a softening cartridge to the system in case of harder water, which extends the service life of all components including the separator.
• What is the warranty on this product? We provide a standard statutory warranty of 2 years from the date of sale on the WHV 35 distributor with built-in low-loss header.

Difference between the WHV 35 and separate WH series low-loss headers

Separate Vaillant WH series low-loss headers (WH 27, WH 40, WH 95, WH 160) only perform the function of hydraulic separation of the boiler circuit from the heating circuits, without a built-in distributor function – a separate distributor for the required number of circuits (for example a distributor for 2 or 3 circuits) must therefore be purchased additionally. The WHV 35, on the other hand, combines both functions in a single body, which is advantageous especially for simpler dual-circuit systems where higher flow capacity than the larger WH series headers is not needed. For systems with a higher number of circuits or a greater total heat loss of the building (for example apartment buildings or larger facilities), it is more suitable to choose a combination of a separate, more powerful low-loss header with a distributor for the required number of circuits.

Typical placement in the system

In a typical installation, the WHV 35 is located directly behind the boiler, in close proximity to the plant room or boiler room, from where short pipe sections then lead to each of the connected pump groups. This arrangement minimises heat losses on the pipework between the separator and the pump groups, and also simplifies future maintenance, since all key system components (boiler, low-loss header, pump groups) are concentrated in one place.

Overview table – Vaillant distributors and low-loss headers

This table helps you quickly get an overview of the range of accessories for Vaillant multi-circuit systems and choose the right combination of components according to the number of circuits and the total flow capacity of the system.

Effect of hydraulic separation on boiler lifespan

In addition to control comfort, proper hydraulic separation via the low-loss header also has a direct impact on the lifespan of the boiler itself. Without this separation, the boiler may enter a state of frequent burner on/off switching (so-called cycling) when thermostatic valves or mixing valves close on the heating side, which increases the mechanical and thermal stress on the heat exchanger and shortens its lifespan. Thanks to its built-in low-loss header, the WHV 35 effectively prevents this phenomenon, as the boiler circuit "sees" a practically constant hydraulic resistance regardless of the current state of the heating circuits.

Aesthetic and space-saving advantages

The compact body of the WHV 35 with white thermal insulation visually matches the design of ecoTEC series boilers and other components of the VDM system. Compared to a combination of two separate parts (distributor + low-loss header), the WHV 35 also saves valuable space in the plant room, which is especially appreciated in smaller boiler rooms or when installing in a cabinet or niche. Fewer separate components also means fewer installation joints, and thus a lower risk of future leaks.