Vaillant connection adapter for PHE S 120-70 to 35 mm Cu pipe

Vaillant connection fitting for PHE S 120-70 to 35 mm Cu pipe

Vaillant plate heat exchangers of the PHE S and PHE C series are among the key components of large professional boiler rooms, cascade connections of condensing boilers and industrial heating hubs. Their role is to hydraulically and thermally separate the primary circuit (heat source – boiler, boiler cascade, heat pump) from the secondary circuit (distribution system, underfloor heating, radiator circuits, domestic hot water heating), while heat is transferred between the circuits exclusively through a set of stainless steel plates – without any direct mixing of media. In practice, this principle is used everywhere it is necessary to prevent mutual hydraulic interference between the circulation pumps of individual circuits, to balance different flow rates, or to separate circuits with different quality, pressure or composition of the heat transfer medium (e.g. glycol mixtures in a solar or heat pump circuit from ordinary heating water in the distribution system).

When installing the Vaillant PHE S 120-70 plate heat exchanger (code 0020137069) into a system with copper piping, it is necessary to bridge the difference between the exchanger's threaded connection and the soldered or pressed copper pipe. This is exactly the purpose of the connection fitting for a 35 mm Cu pipe – an original Vaillant adapter piece which has a thread matching the connection of the PHE S 120-70 exchanger on one side (1 1/4" screw connection) and a plain end for soldering or pressing with a copper pipe of 35 mm outer diameter on the other side – a commonly used dimension in the piping of larger professional heating systems and boiler rooms.

Why a bridge between the thread and the copper pipe is needed

Vaillant PHE S series plate heat exchangers have a standardized screwed (threaded) connection from the factory, which is universally usable across different types of piping systems – steel threaded, press systems and copper piping. When choosing a copper piping system (popular especially for its corrosion resistance and long service life with properly treated heating water), it is necessary to use a suitable adapter that enables a clean and tight connection without the need for additional universal couplings or custom adaptation. This original Vaillant part precisely solves this exact case for the 35 mm Cu dimension, which corresponds to the power class of the PHE S 120-70 model.

Technical data

Overview of the entire Vaillant PHE series (official manufacturer technical data)

Plate material: stainless steel. Operating temperature (plate material range): -196 °C to +200 °C. The PHE S model has a screwed (threaded) 1 1/4" connection, PHE C models have a flanged connection. Source: Vaillant assembly manual "Externer Plattenwärmetauscher PHE S, PHE C", document 0020196730_00.

Installation

1. Before installation, check the cleanliness of the thread on the exchanger's connection stub and the inside of the adapter piece.
2. Apply a suitable sealant to the threaded connection (hemp fiber with sealing paste or Teflon tape intended for heating systems).
3. Screw the fitting onto the exchanger's connection stub and tighten with appropriate force using suitable tools – excessive tightening may damage the thread, insufficient tightening may cause leakage.
4. Connect the 35 mm outer diameter copper pipe to the plain end of the fitting by soldering or pressing according to the chosen system and standard procedures of that technology.
5. After installation, before insulation and final commissioning, perform a pressure test of the joint's tightness.

Installation principles (according to the official Vaillant assembly manual 0020196730_00)

• Installation only in areas without risk of freezing.
• Ensure sufficient space for operation, servicing, venting and draining of the exchanger.
• Connections are always led out to the side, never from below the exchanger.
• To minimize pressure losses, a vertical installation position is recommended.
• The PHE C model must always be additionally anchored to a floor bracket with height-adjustable feet (10 – 55 mm) – it must never be left hanging solely on the pipe connections.
• The flow of the primary and secondary sides is routed in counterflow – ensuring the highest heat transfer efficiency.
• Maximum allowable forces and moments on the connections: tensile force T, transverse force F, bending moment Mb and torque moment Mv – see the table below to prevent mechanical damage to the connections during pipe installation.

Why it is important to use an original adapter piece and not a universal fitting

A number of universal thread-to-copper-pipe fittings are commonly available on the market, which at first glance look the same. However, in professional heating assemblies with high output (in this case up to 120 kW through one connection point), precise dimensional and material design matters: an imprecise thread can cause micro-leaks that only appear after several months of operation due to temperature cycles (alternating heating and cooling of the joint when starting up and shutting down the boiler room), and an unsuitable adapter material can lead to galvanic corrosion at the contact point with the exchanger's stainless steel connection stub. An original Vaillant part, on the other hand, is designed and tested directly by the system manufacturer as part of an approved assembly, eliminating these risks and preserving the warranty claim in case of a complaint about the connection's functionality.

Typical use scenario

Imagine the renovation of an older boiler room in an apartment building, where the original heat distribution piping is made of copper pipe with an outer diameter of 35 mm – a common dimension for distribution systems with an output of roughly up to 100 – 150 kW. The investor decides to replace the original, aging heat exchanger with a new Vaillant PHE S 120-70 model, but does not want to change the existing and functional copper piping throughout the building. It is precisely in this case that this connection fitting allows an elegant and quick connection of the new exchanger to the original piping without the need to replace an entire section of the piping or use temporary universal couplings, which could be a source of future leakage problems.

Difference between threaded (BSP) and metric connections

The 1 1/4" designation on the connection stub of the PHE S 120-70 exchanger is based on the internationally used system of British Standard Pipe threads (BSP), common throughout Europe in heating and water supply technology. Copper piping, on the other hand, is dimensioned according to metric outer diameter (in this case 35 mm) – the adapter piece therefore has to correctly bridge both labeling systems as well as the actual physical dimensions, which is precisely the task this original part is designed for.

Compatibility and related accessories

This fitting is intended exclusively for the PHE S 120-70 model (code 0020137069). When completing the assembly with the exchanger, we also recommend adding the original thermal insulation for the exchanger (code 0020248922), which protects the boiler room operator from contact with a hot surface and reduces heat losses – both parts are available separately in this category on atria.sk.

Why choose the original Vaillant adapter piece

• Precise dimensional and threaded design matching the connection stub of the PHE S 120-70 exchanger – without risk of thread mismatch as with generic universal fittings from the general market.
• Material suitable for long-term operation in heating systems.
• Simple and quick installation without the need for additional machining.
• Preservation of the exchanger's warranty conditions when using original Vaillant accessories.
• Verified combination of materials against the exchanger's stainless steel connection stub, reducing the risk of galvanic corrosion at the joint compared to unverified combinations of materials from various manufacturers.

Summary – when to order this part

Always order this connection fitting when you plan or are already carrying out the connection of a Vaillant PHE S 120-70 plate heat exchanger to an existing or newly built copper pipe distribution system with an outer diameter of 35 mm. For a different type of piping (steel threaded pipe, a press system of a different diameter, or a flanged connection of PHE C series models), this specific part is not suitable and a corresponding alternative from the Vaillant accessories range should be chosen.

The combination of the PHE S 120-70 plate heat exchanger, the original connection fitting for a 35 mm Cu pipe, and shaped thermal insulation (code 0020248922) represents a complete, manufacturer-verified solution for connecting a small to medium cascade of condensing boilers to a copper heating system distribution network – without the need to combine parts from different manufacturers or rely on unverified universal components from a general installation materials wholesaler.

Frequently Asked Questions