Vaillant mechanical check valve, Ø 110 mm

Product detailed description

Vaillant mechanical backflow flap Ø 110 mm – protection when connecting multiple boilers to a shared flue

The mechanical backflow flap with a diameter of 110 mm (code 0020207200) is genuine Vaillant safety accessory intended primarily for cascade connections of condensing boilers, i.e. situations where multiple boilers are connected to a shared vertical flue gas path (shared chimney, common flue collector, or a shared LAS-type shaft). Its purpose is to prevent flue gases from operating boilers from flowing back into a boiler that is currently out of operation, through its own, currently inactive flue gas connection.

Without this component, in a cascade connection flue gases from running boilers could be pushed back through the shared flue gas path into the switched-off boiler and potentially escape into the boiler room, which represents both a safety risk and a risk of damage to the inactive unit from condensate and heat originating from other sources.

Operating principle of the mechanical backflow flap

The mechanical backflow flap works on a simple yet reliable principle: it contains a movable flap blade (or a set of blades) which opens when flue gases flow from the operating boiler due to the overpressure created by that boiler's flue gas fan, and closes again by its own weight or by spring action once operation stops. In this way, the flap allows flue gases to pass in only one direction – out of the system – and prevents them from flowing back into a switched-off unit. It is therefore not an electronically controlled component, but a purely mechanical solution that requires no power supply or connection to the boiler's control unit, which increases its reliability and reduces the risk of failure.

The 110 mm diameter corresponds to one of the standard dimensions used in Vaillant system solutions for connecting multiple sources to a shared flue gas path, and the flap is designed to be installed directly into the flue duct near the point where an individual boiler connects to the collector pipe.

When this flap is essential

• Cascade boiler rooms – residential buildings, office buildings, industrial and commercial facilities where, for capacity or backup reasons, multiple condensing boilers are installed and connected to one shared flue gas path,
• Shared chimney systems (LAS) – residential buildings with a shared air-flue shaft, where multiple individual apartment boilers are connected to a single vertical duct,
• Backup/redundant configurations – installations where one boiler serves as a backup for another and it must be guaranteed that, while one source is operating, the other (switched off) remains safely isolated from the flue gas flow,
• Extensions of existing boiler rooms – when adding another boiler to an already functioning flue gas path, fitting a flap on each new as well as existing connection point is a safety requirement of the project.

For a single boiler with its own independent flue gas path (not connected to a shared system), this flap is generally not required – its use is specifically tied to scenarios with a shared flue gas path.

Installation and placement in the system

The flap is installed in the flue duct near the flue gas outlet of the specific boiler, before it connects to the shared collector branch or shaft. The flow direction marked on the flap body must correspond to the actual direction of flue gas flow from the boiler out of the system – incorrect orientation during installation would completely negate the device's function. Installation should be carried out by a trained service technician qualified to install gas appliances and flue gas systems, ideally as part of a cascade connection project that specifies the exact placement and number of flaps required.

It is also important to ensure the flap remains accessible for future inspection and possible replacement, since it is a mechanical component with a movable blade which – although designed for long-term maintenance-free operation – may over the years of operation be exposed to the buildup of condensate and impurities from flue gases.

Relation to the safety of cascade boiler rooms

When designing cascade boiler rooms, backflow of flue gases is one of the key safety topics addressed both in the manufacturer's technical documentation and in applicable standards for designing shared flue gas paths (in particular EN 15287 and related technical rules for cascade connections of gas appliances). The absence or failure of a backflow flap in a multi-source connection can lead to flue gases entering the boiler room through an inactive boiler, posing a risk both to operator safety and in terms of carbon monoxide concentration in an enclosed space. This is precisely why this flap is a common, and often project-mandated, part of every cascade solution with Vaillant condensing boilers.

Material and durability

The flap is made of materials resistant to the condensate produced during the operation of condensing technology (mildly acidic environment with a pH of approximately 3.5 to 5.5) and to the flue gas temperatures typical of condensing boilers (typically up to approx. 80 °C at the outlet of the flue gas path at lower heating system temperature gradients). Both the blade and the flap body are designed to retain their functionality and tightness even after long-term operation, without the need for lubrication or other regular maintenance.

Compatibility

This 110 mm diameter backflow flap is intended for use in Vaillant system solutions for cascade and collector flue gas paths with condensing gas boilers of the ecoTEC, ecoTEC plus, ecoTEC exclusiv series and related models with output corresponding to this pipe diameter. Before ordering, we recommend verifying the exact diameter of the flue gas path designed for the specific cascade, as Vaillant offers flaps in several diameter versions (for example also with a reduction to 80/110 mm for other boiler combinations).

Maintenance and inspection

Although the mechanical backflow flap is designed as a maintenance-free component, it is recommended to check its functionality and the free movement of the blade as part of the regular annual service inspection of the entire cascade boiler room. The inspection should mainly verify that the blade moves freely and smoothly without sticking caused by condensate deposits, and that the sealing surfaces of the flap are not damaged or corroded. In cascade boiler rooms with intensive operation (for example in residential buildings or commercial facilities with high hot water and heating consumption), it may be advisable to include flap inspections in shorter service intervals as recommended by the service organization.

Why choose a genuine Vaillant part

Using a genuine Vaillant backflow flap instead of a universal alternative guarantees that the flap's dimensional and functional parameters exactly match the requirements of the system for which the cascade connection is designed – including the pressure drop that the flap introduces into the system, which must be taken into account when sizing the flue gas fan output of individual boilers. An incorrectly sized or incompatible flap from another manufacturer can cause either insufficient sealing when the boiler is switched off, or, conversely, excessive pressure drop restricting the flue gas path's performance.

Frequently Asked Questions (FAQ)

Do I need this flap even with a single standalone boiler?
No, for a standalone installation of a single boiler with its own non-shared flue gas path, a backflow flap is generally not needed. Its use is tied to connections where multiple sources share a common flue gas path.

How many flaps do I need for a cascade of three boilers?
The exact number and placement of flaps is determined by the cascade connection project based on the configuration of the collector pipe, but typically a flap is fitted at the connection of each individual boiler to the shared branch, meaning usually three flaps for three boilers.

Does the flap require electrical power or a connection to the boiler control unit?
No, it is a purely mechanical component operating on the principle of pressure difference and the blade's own weight/spring, without the need for electrical power or control.

What happens if the flap freezes or gets stuck in the open position?
If stuck in the open position, the flap loses its protective function and the system behaves as if the flap were not fitted at all – this is why regular inspection of its free movement during servicing is important, especially in boiler rooms with higher humidity or lower operating temperatures.

Is this flap also suitable for shared LAS-type chimney systems in residential buildings?
Yes, one of the main uses of this flap is precisely when connecting individual apartment condensing boilers to a shared air-flue shaft, where it protects against backflow of flue gases between individual apartments.

Must installation be carried out by a certified technician?
Yes, given the safety nature of this component and its connection directly into the flue gas path, installation should always be entrusted to a professionally qualified person authorized to install gas appliances and flue gas systems.

Typical mistakes in the design and installation of cascade flue gas systems

When implementing cascade boiler rooms, service and installation companies most often encounter the following shortcomings related to backflow flaps:

• Omitting the flap during a later cascade extension – when an additional boiler is added to an existing boiler room, the investor or installation company sometimes fails to fit a flap on the original, already operating boilers as well, resulting in an asymmetric and dangerous configuration,
• Incorrect flap orientation during installation – reversing the flow direction marked on the flap body results in the flap either not performing its function at all, or, conversely, blocking even the correct flow of flue gases from the operating boiler,
• Underestimating the flap's pressure drop during design – in cascades with a longer flue gas path and multiple flaps, the sum of pressure drops can exceed the flue gas fan's reserve, resulting in reduced output or fault messages from the boiler,
• Missing record of the flap type and position in project documentation – this complicates future servicing, especially if the cascade is serviced by a different company than the one that originally installed it.

Strict compliance with the manufacturer's design documentation for the specific type of cascade connection is therefore just as important as selecting the correct type of flap.

Difference between mechanical and motorized backflow flaps

Besides mechanical backflow flaps such as this product, some larger or more complex cascade systems also use motor-driven flaps connected to the boiler's control unit, which actively open and close in sync with the operating status of the given source. A mechanical solution such as this flap has an advantage over the motorized variant in its simplicity, the absence of electronic components prone to failure, and independence from the functionality of the boiler's control electronics – it works purely on the physical principle of pressure difference. For most common cascade connections in residential buildings and smaller commercial boiler rooms, the mechanical solution is fully sufficient and is also more cost-effective than motorized alternatives.

Connection to chimney design and diameter sizing

The choice of a 110 mm diameter for the backflow flap must correspond to the diameter of the rest of the flue gas path and be consistent with the overall chimney sizing calculation, which in cascade systems takes into account the sum of the rated heat inputs of all connected boilers, the height and directional configuration of the route, and the pressure drops of all installed components including bends, reductions, and backflow flaps themselves. This calculation should be carried out by an authorized flue gas path designer or a qualified chimney sweep specialist, typically using chimney sizing software tools accepted by the boiler manufacturer.

Storage and handling before installation

Until installation, the flap should be stored in a dry, clean environment free of mechanical load that could deform the body or blade. When handling, care must be taken to ensure the blade does not become stuck in either the open or closed position due to excessive pressure or improper handling, as this is a precision mechanical component whose correct function depends on the free and smooth movement of the blade throughout its entire range.

Summary

The Vaillant mechanical backflow flap Ø 110 mm is a key safety component in every cascade or shared connection of condensing boilers to a common flue gas path. It prevents flue gases from flowing back into inactive sources, works reliably without the need for electrical power, and as a genuine Vaillant part guarantees precise technical parameters that meet the requirements of this brand's cascade systems, including a guaranteed pressure drop and long-term mechanical reliability.

Additional technical considerations for designers

When designing a cascade boiler room, it is necessary to account for the fact that each installed backflow flap introduces a certain pressure drop into the flue gas path, which must be taken into account in the overall calculation of the hydraulic (or aerodynamic) resistance of the flue gas route and when selecting the flue gas fan output of individual boilers. The cascade designer should obtain this figure from the manufacturer's technical documentation for the specific flap type and take it into account together with the pressure drops of other components (bends, branches, collector pipe) so that the resulting flue gas path remains within the parameters guaranteed by the boiler manufacturer for the given type of connection.

Recommendations for choosing a supplier and installation company

Given the safety importance of backflow flaps in cascade systems, we recommend entrusting their selection and installation to a company with proven experience in installing multi-source Vaillant boiler rooms, ideally with references for similar projects. An experienced company can take into account not only the flaps themselves during design, but also the overall concept of the collector flue gas path, including future possibilities for extending the cascade with additional sources, which saves costs in the event of later boiler room modernization.

Relation to inspection activities and chimney checks

Since the backflow flap is part of the flue gas path, it is subject, like other components, to regular inspection as part of mandatory chimney and flue gas path inspections carried out by an authorized person (chimney sweep) in accordance with applicable legislation. In cascade boiler rooms, it is advisable to record the position and type of installed flaps directly in the flue gas path inspection log, so that both the chimney sweep and the service technician have a clear overview of the number, type, and exact location of all safety components in the system during each subsequent inspection, which significantly shortens the time needed to carry out the inspection or any service intervention.