Vaillant VDM pump assembly for two-circuit heating (direct/mix)

Product detailed description

Vaillant VDM assembly for two-circuit heating (direct/mix) – complete turnkey solution

The high-efficiency electronic VDM pump assembly for two-circuit heating (order number 0020193145) is a complete, factory-matched package for a multi-circuit heating system, comprising a two-circuit manifold with a built-in hydraulic low-loss header and two pump groups – one direct (VDM 10) and one mixing (VDM 20 M or VDM 25 M). Instead of purchasing and combining individual components separately, this assembly offers a proven, mutually compatible solution for a typical two-circuit heating scenario – a combination of a radiator circuit (direct group) and underfloor heating or another low-temperature branch (mixing group).

What exactly the assembly includes

• Two-circuit manifold with a built-in hydraulic low-loss header, including a low-loss header sensor, mounting brackets, and thermal insulation
• VDM 10 direct pump group – high-efficiency class A electronic pump, 230 V, two circuit thermometers, complete insulation
• VDM 20 M / VDM 25 M mixing pump group – high-efficiency class A electronic pump, three-way mixing valve with a 230 V actuator, two circuit thermometers, complete insulation
• 120 mm mounting spacing between individual manifold outlets
• Complete set of connecting and sealing material needed to assemble the whole block

Why choose a ready-made assembly instead of individual components

Buying a complete assembly brings several advantages over sourcing the manifold, low-loss header, and two pump groups separately. First, guaranteed mutual compatibility of all hydraulic parameters – flow characteristics, pressure losses, and mechanical dimensions are factory-tuned to work together without the need for additional adjustment. Second, simpler logistics and ordering – instead of three or four separate items, a single order code is sufficient. Third, generally a more favorable total price compared to the sum of prices of individual components purchased separately. Finally, a uniform appearance and easier installation, since all parts share the same 120 mm mounting spacing and the same visual design (white body, shaped insulation).

How the combination of the direct and mixing group works

This particular assembly is designed for the most common multi-circuit heating scenario in family houses – one circuit with the same temperature as the boiler (typically radiators, connected via the direct VDM 10 group without any temperature change) and one circuit with a lower, precisely regulated temperature (typically underfloor heating, connected via a mixing group with a three-way valve that mixes cooler return water with warmer water from the boiler circuit). Both groups are connected to a common manifold with a built-in low-loss header, which hydraulically separates the boiler circuit from both heating branches, so that flow changes on the heating side (for example, thermostatic radiator valves closing) do not affect the flow stability through the boiler itself.

Installation and commissioning

• The manifold with the built-in low-loss header is mounted on the wall of the utility room using the supplied brackets, near the boiler
• The flow and return pipes from the boiler are connected to the inlet side of the low-loss header
• Both pump groups are connected to the outlet side of the manifold with 120 mm spacing
• The low-loss header sensor is connected to the boiler controller, and the mixing valve actuator to the respective room or weather-compensating controller of the given circuit
• After electrical connection, complete thermal insulation is fitted onto all parts of the assembly
• The system is filled with water, thoroughly vented, and the correct function of the control on both circuits is verified before handover to operation

Compatibility

The assembly is designed to work with Vaillant ecoTEC plus, ecoTEC pro, and ecoTEC exclusive condensing boilers (including newer models with IoniDetect technology) and with sensoCOMFORT, sensoNET, and multiMATIC controller series. The 120 mm spacing matches the entire range of Vaillant pump groups and manifolds, so the assembly can be supplemented in the future with additional pump groups if the system needs to be expanded with another circuit (for example, when replacing it with a manifold with a higher number of outlets).

Maintenance

• Once a year, ideally before the heating season, check the function of both pumps and the mixing valve actuator
• Verify the function of the low-loss header sensor and its connection to the boiler controller
• Check the tightness of all screw connections, especially after the first heating season
• Monitor the thermometers on both circuits – significant deviations from expected values may indicate a fault or the need for hydraulic balancing
• With harder water, consider a softening cartridge, which extends the service life of the pumps, valve, and the low-loss header itself

Why choose this particular assembly

For builders and installation companies implementing a new two-circuit system from scratch, this assembly represents the simplest and at the same time the most reliable path to a functional, mutually compatible solution. Instead of separately selecting and combining a manifold, low-loss header, and two pump groups (with the risk of an incorrect combination of parameters), you get a proven package directly from the boiler manufacturer, with the guarantee that all components work together seamlessly, including cooperation with Vaillant control technology.

Comparison with the other available assembly (mix/mix)

Choose the direct/mix assembly if your system has one circuit that can operate directly at the boiler temperature (most often radiators) and another circuit requiring a lower, regulated temperature (underfloor heating). If you need to control the temperature independently on both circuits (for example, two underfloor heating zones with different requirements), choose the mix/mix assembly instead.

Frequently Asked Questions

• What is the difference between the direct/mix assembly and buying components separately? The assembly includes a pre-matched manifold with a built-in low-loss header and two pump groups in one package, which guarantees compatibility and generally works out cheaper than the sum of the prices of individual components purchased separately.
• Can the assembly be expanded with a third circuit later? The built-in low-loss header in the manifold has a fixed number of two outlets. If you plan to expand to more circuits, we recommend considering a separate, larger low-loss header with a manifold for the required number of circuits instead of this compact assembly.
• Which circuit should be connected to the direct group and which to the mixing group? Connect the circuit with the same temperature as the boiler (typically radiators) to the direct group, and the circuit requiring a lower, regulated temperature (typically underfloor heating) to the mixing group.
• Does the assembly include controllers for the individual circuits? No, controllers (room, weather-compensating, or system) are ordered separately according to the customer's requirements and the needs of the individual circuits.
• What is the warranty on this assembly? We provide a standard statutory warranty of 2 years from the date of sale on the complete VDM pump assembly for two-circuit heating.
• Is the price of the assembly more favorable than buying the parts separately? Yes, a discounted special price is currently available for this assembly compared to the standard list price, making it an economically advantageous choice for a planned two-circuit system installation.
• Is the assembly also suitable for renovations of older houses? Yes, as long as the boiler is also being replaced with a new Vaillant ecoTEC condensing model as part of the renovation, and a second heating circuit is being built or added at the same time, for example underfloor heating in a house that originally only had radiators, which is a common and proven way of modernizing heating during a more complex renovation.

Detailed look at the direct group in the assembly

The VDM 10 direct group included in this assembly features a high-efficiency electronic circulation pump of energy efficiency class A with automatic speed control, two circuit thermometers for instant visual temperature checks, and complete thermal insulation made of shaped EPP. Since it has no built-in temperature control, it delivers exactly the water temperature currently provided at the low-loss header outlet to the connected circuit (i.e., essentially the boiler circuit temperature, adjusted only by the minimal pressure loss across the low-loss header). This feature is desirable precisely for radiator circuits, where no additional temperature control is needed beyond what is already provided by the boiler itself and its weather-compensating controller.

Detailed look at the mixing group in the assembly

The mixing group (VDM 20 M or VDM 25 M, depending on the specific assembly configuration) includes, in addition to the class A electronic pump, a three-way mixing valve with a 230 V electric actuator. The actuator is controlled by a room, weather-compensating, or system controller and gradually mixes cooler return water from the secondary circuit with warmer water from the low-loss header, thereby maintaining the required, lower temperature of the water entering the connected low-temperature circuit – most often underfloor heating. This control is essential to prevent exceeding the maximum floor surface temperature and potential damage to sensitive floor coverings such as wood or laminate.

Benefit of the built-in low-loss header within the assembly

The built-in hydraulic low-loss header inside the manifold body plays a key role in hydraulically separating the boiler circuit from both connected heating branches. As a result, flow changes caused by closing thermostatic radiator valves or cycling of the mixing valve on the underfloor circuit do not affect the flow stability through the boiler itself, which reduces the risk of unwanted burner cycling and extends the life of the heat exchanger. The low-loss header sensor also provides the boiler controller with information about the current state of the secondary side of the system, allowing more precise adjustment of the boiler's output to the actual needs of both connected circuits.

Typical deployment scenario in a family house

Imagine a typical family house with a Vaillant ecoTEC plus condensing boiler, where the living area of the house (living room, kitchen) is heated by underfloor heating and the upper floor with bedrooms is heated by conventional radiators. In this case, the radiator circuit is connected to the VDM 10 direct group (with no need for further temperature control, since radiators can handle even higher water temperature from the boiler circuit), and the underfloor heating is connected to the mixing group, which lowers the water temperature for the floor to a safe and comfortable level, typically 35–40 °C. Both circuits are hydraulically separated from the boiler thanks to the built-in low-loss header, so the control of one circuit does not affect the stability of the other.

Recommendations for installation companies and designers

When designing a system with this assembly, we recommend checking the sum of the flow rates of both connected circuits against the capacity of the built-in low-loss header to avoid hydraulic overload. For typical family houses with a boiler output of up to approximately 25–30 kW, this assembly generally provides a sufficient reserve for both circuits. For larger buildings or a higher number of parallel branches on one of the circuits, we recommend considering separate components with higher flow capacity instead of this compact assembly.

Economic advantage of the solution

When comparing the price of this complete assembly with a hypothetical sum of the prices of a separate manifold with a built-in low-loss header (for example, WHV 35), a separate VDM 10 direct group, and a separate VDM 20 M or VDM 25 M mixing group, the assembly generally works out cheaper, especially if a discounted special price is currently available. This saving, together with guaranteed compatibility of all components and a simpler ordering process, makes the assembly an attractive choice especially for builders implementing a new heating system from scratch, where no existing manifold or low-loss header from another manufacturer is already tied into the system.

Summary

The high-efficiency electronic VDM pump assembly for two-circuit heating (direct/mix) represents a proven, comprehensive solution for the most common multi-circuit heating scenario in family houses – a combination of a radiator and an underfloor heating circuit. Thanks to the built-in hydraulic low-loss header, two mutually matched pump groups, and a uniform visual design, it offers fast, reliable, and aesthetically coherent installation directly from the boiler manufacturer, with a guarantee of mutual hydraulic and mechanical compatibility of all parts that cannot be achieved to the same degree of certainty when combining individual parts from different manufacturers.