How to correctly install a fixed pipe bend for 15–18 mm pipes

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How to correctly install a fixed pipe bend for pipe 15–18 mm

Correct installation of a fixed bend belongs to those tasks that at first glance appear simple – but in practice, it is precisely here that the most errors occur, which later manifest as leaks, mechanical stress on the pipe or uncontrolled expansion. If you are working with copper or plastic (PB/PE) pipe with a diameter of 15 or 18 mm – i.e. with dimensions that are most commonly used in domestic heating and hot water supply installations – this article will provide you with a comprehensive guide: from the principle of why a fixed point in the pipe route is needed, through the selection of suitable fastening elements, to the step-by-step installation process, including typical errors from practice.

This article is part of our Knowledge Center for the installation tools section. Related topics that you may encounter during the planning of the installation can be found under the titles How to choose the right installation tools for Hepworth pipe, Clips vs. brackets for pipe mounting – when to use which, or Common errors in pipe mounting and how to avoid them – I recommend reading them in combination with this guide.

What is a fixed bend and why is it necessary

In every pipe route, temperature changes occur during operation. Copper pipe expands by approximately 0.17 mm per meter of length with a temperature increase of 10 °C. PB (polybutene) pipe has an even higher coefficient of thermal expansion – approximately 0.13–0.15 mm/m/°C. At first glance, these numbers are negligible, but with a 10-meter section and a temperature fluctuation of 50 °C (for example, when starting heating after a summer break), we are talking about an extension of up to 75 mm. This extension has to go somewhere – either it is controlled and directed through an expansion elbow or loop, or it will uncontrolledly manifest in the weakest point of the entire route: in the coupling, in the valve or at the mounting point.

A fixed point (also fixed bend, fixing point, in German technical terminology Festpunkt) is a location in the pipe route where the pipe is firmly anchored and where the movement of the pipe axis is zero. All expansion is derived from this point in both directions – i.e., by rigid fixing at one point, you divide the pipe section into two controlled parts, with each one expanding towards the nearest expansion element (compensator, loop, elbow).

Without a fixed point, the pipe would "float" as a whole when heated and would pull all adjacent valves, couplings and branches along with it. In practice, I have seen cases where the missing fixed point on the main riser caused the floor heating distributor to literally detach from the wall after three seasons – not because the material was bad, but because no one thought about fixing the riser before the distributor.

Difference between a fixed point and a sliding support

Before we proceed to the actual installation, it is essential to understand the difference between the two basic types of pipe support:

Sliding support (guiding point) – the pipe is supported in such a way that it can slide longitudinally. The clip or bracket holds the pipe in the axis, prevents lateral movement, but does not restrict longitudinal movement (expansion). This is the most common type of support used on most of the route length.
Fixed support (fixed point) – the pipe is firmly held in such a way that movement in all directions is prevented. The fixed point transfers the forces generated by expansion into the building structure (wall, ceiling, floor).

In practice, a fixed point is implemented either by a special fixed bend (rigid clamping of the pipe without clearance) or by a combination of a standard bracket/clip with welding, screwing or another rigid connection directly to the pipe. For diameters of 15–18 mm, in the Hepworth system and compatible installations, pipe mounting brackets for 16 mm pipe and pipe mounting brackets for 16–18 mm pipe are most commonly used – with the fixed point being made by tightening rigidly and additional fixing so that the pipe has no axial clearance.

Where to place a fixed point in the pipe run – rules and examples from practice

Placing a fixed point is not random, but follows several rules that are the result of physical laws and years of installation practice:

Basic rules for placing a fixed point

Before and after a fitting – valves, ball valves, control elements and distributors must be protected from the forces exerted by expanding pipe. The fixed point is placed as close as possible to the fitting, maximum 200–300 mm from it.
In the middle of a long section – for a straight run longer than about 3–4 m without a natural compensator (elbows, bends), it is necessary to place a fixed point in the middle of the section and to install sliding supports and compensators at both ends.
At the beginning and end of a riser – vertical risers are especially prone to expansion forces, because when heated they "grow" upwards. A fixed point on a riser is placed in the lower third of its length (closer to the base of the riser).
At a wall or ceiling penetration – a penetration through a building structure can function as a natural fixed point, if the pipe is firmly embedded or clamped in the penetration – however, be careful to always have a protective sleeve (pipe protector), so that thermal expansion does not cause cracking of the plaster.
Maximum distance between compensators for a diameter of 15–18 mm – approximately 6–8 m for copper, 3–5 m for plastic pipe, always with a fixed point in the middle.

From practice: one of the most common problems I encounter during inspections of older installations is the complete absence of a fixed point on horizontal runs in the basement. Installers there often install the pipe with evenly spaced sliding supports along the entire length – the pipe may look nice, but after the first heating it starts to push into the manifold and after years the result is cracks in the welds or loose connections.

Material and dimensional specifications for 15 and 18 mm pipe

Diameters of 15 mm and 18 mm belong to the most commonly used in domestic installations. Typical applications:

15 mm (outer diameter) – radiator connections, outputs from floor heating manifolds, connections to sinks and basins, short sections to radiators. Medium: water at temperatures of 30–75 °C.
18 mm (outer diameter) – main runs to multiple radiators, horizontal secondary branches, sometimes also risers in smaller apartment buildings.

Important: in the Hepworth and compatible systems, work is done with the outer diameter of the pipe, not with the nominal diameter. Therefore, a bracket or clamp marked "16 mm" fits a pipe with an outer diameter of 16 mm – this corresponds to standard PB/PE pipe marked DN10 or copper pipe 15×1 (outer diameter 15 mm). Always measure the actual outer diameter with a caliper before purchasing – the nominal diameter on the pipe and the actual outer diameter may differ.

For connecting copper pipe to threaded fittings in the vicinity of a fixed point, it has proven effective to use threaded compression fitting for copper pipe 15×1 EK – this is a reliable mechanical connection without the need for soldering, which is important when implementing a fixed point at a location where you want to have the possibility of disassembly. For combined runs of copper and plastic PB pipe, use threaded compression fitting 15×1 EK for copper or PB pipe, which handles both materials in one version.

Step-by-step installation procedure for a fixed loop

Below I describe a proven procedure from practice for installing a fixed point on a 15–18 mm pipe in a domestic installation. I assume that the pipe is running along a wall or in a shaft, and that the structure allows for mounting a bracket (masonry, concrete, gypsum board with appropriate anchors).

Tools and materials

Hammer or drill with appropriate drill bit (6–8 mm for masonry, 10 mm for concrete)
Anchors suitable for the substrate (in concrete at least anchors with a tensile strength ≥ 0.5 kN)
KOMBI M8 screws – universal combination screws for mounting the bracket to the wall
Torque wrench or screwdriver
Pipe bracket for 16–18 mm suitable for your diameter
Tape measure
Level (at least 60 cm)
Pencil, measuring tape

Step 1: Determining the position of the fixed point and marking

First, determine on the unfolded layout (or at least in your mind) exactly where the fixed point should be. Mark the position on the wall with a pencil. Check whether there is electrical installation in the wall at that location (using a detector). Verify the wall material – this determines the type of anchor.

In the case where the fixed point is to be placed near a fitting, measure the distance from the axis of the fitting and place the bracket no more than 150–200 mm from the axis of the coupling or valve. The closer, the better – a shorter lever arm means less bending stress on the fitting.

Step 2: Drilling and installing the anchor

Drill a hole corresponding to the diameter of the anchor. For standard masonry (brick, aerated concrete), use a plastic expansion anchor 8 mm, for concrete rather metal expansion anchors. Drilling depth: at least 50 mm into masonry, 60 mm into concrete. Clean the hole (blow out or clean with a brush), insert the anchor.

Step 3: Screwing the bracket

Place the pipe bracket against the wall, check with a level whether it is in a horizontal (or vertical) position according to the direction of the run. Screw the KOMBI M8 screw – first by hand, then tighten with a screwdriver. Attention: tighten the fixed bracket to full torque – unlike sliding brackets, where a small clearance is sometimes deliberately left, here you want zero movement. Recommended tightening torque for M8 in a plastic anchor is 4–6 Nm, for a metal anchor 8–10 Nm.

Step 4: Inserting the pipe and fixing

Insert the pipe into the bracket. In fixed support, the pipe must be in the bracket without axial clearance. If the bracket has a closing clip or screw closure, close it and tighten according to the manufacturer's instructions. If you have a two-part bracket (bottom and top), secure the top and check that the pipe cannot be moved even with slight force along the axis.

Important: Never tighten the bracket so much that it deforms the pipe cross-section – especially with plastic (PB) pipe, ovalization and subsequent increased hydraulic losses or weakening of the wall at the joint location is a risk. With copper this is less critical, but the same rule applies: the pipe must be firmly – not excessively – clamped.

Step 5: Inspection after installation

After completing the installation of the fixed point, check the entire run: sliding supports must allow longitudinal movement of the pipe, the fixed point must be clearly rigid. Before covering the installation (plaster, gypsum board, ceiling), I recommend performing a pressure test and a test heating – observe whether the pipe near the fixed point shows any abnormal stress or deflection.

Common mistakes when installing fixed points and how to avoid them

Over the years of working on piping installations, I have managed to collect a whole collection of mistakes people make when fixing pipes. I will describe the most common ones, because understanding the mistake is the first step to avoiding it.

Mistake 1: Fixed point at the wrong location

The plumber installs the fixed point not near the valve, but "somewhere in the middle of a straight section", because it was just convenient to drill there. Result: expansion forces flow toward the valve, which is not protected. Solution: always first determine what needs to be protected (valve, splitter, wall penetration), and only then determine the location of the fixed point.

Mistake 2: Using a sliding strap as a fixed point without additional fixation

A standard sliding strap or bracket is not a fixed point, even if you tighten it to the maximum. If it does not have a mechanism that prevents axial movement of the pipe, the pipe will simply slip out during expansion. Solution: use either special fixed clamps for fixed points, or add a mechanical axial stop to a standard bracket – for example, a soldered ring on the pipe right next to the bracket, which prevents sliding.

Mistake 3: Too short or unsuitable type of anchor

A fixed point must transfer forces in the order of hundreds of Newtons into the wall. A 6 mm plastic anchor inserted only 30 mm into aerated concrete is not sufficient. I have seen cases where the entire fixed bracket pulled out of the wall during the first heating season – not because the bracket was bad, but because the anchor was dimensioned for sliding support. Solution: always choose anchors with higher pull-out strength for fixed points, and in aerated concrete use special anchors (e.g. chemical anchoring or frame anchors with a large contact surface).

Mistake 4: Two adjacent fixed points without an expansion joint between them

This is a dangerous mistake. If you place two fixed points too close to each other (e.g. both near adjacent valves on a short run without an expansion joint between them), you lock the pipe into a "cage" and the stress has nowhere to go during expansion. The result is pipe buckling, joint rupture or one of the fixed points being torn off. Solution: there must always be at least one expansion joint (expansion elbow, bellow, flexible loop) between any two fixed points.

Mistake 5: Wrong diameter of bracket or strap

A bracket dimensioned for 18 mm pipe slipped over a 15 mm pipe – that is not a fixed point, that is just decoration. The pipe has so much clearance in the bracket that it moves not only axially, but also laterally. Solution: always measure the actual outer diameter of the pipe and choose a bracket with minimal clearance. For a pipe with an outer diameter of 16 mm (standard PB pipe DN10), the correct choice is a 16 mm bracket, not a 18 mm bracket.

Special situations from practice: risers, corner routes and shafts

Fixed point on a vertical riser

Vertical risers expand upwards when heated. The rule is that the fixed point is placed in the lower third of the riser – specifically about 1/3 of the height from the base. If the riser is 3 m long, the fixed point will be about 1 m from the floor. Sliding supports are placed along the entire length at intervals of 1.0–1.5 m (for copper) or 0.7–1.0 m (for plastic). For long risers over 5 m, consider using two fixed points with an expansion joint (compensating loop) between them.

Corner route – natural expansion joint

If the route makes a 90° bend, the bend itself functions as an expansion joint – when one branch is heated, the force is partially absorbed by the flexibility of the bend. This is true only if the branches of the bend are long enough (at least 15–20× pipe diameter, i.e. for 18 mm pipe about 300–360 mm free length before and after the bend). In such a case, the fixed point is placed at the end of the longer arm, the bend functions as an expansion joint and the shorter arm has sliding supports.

Installation in a shaft

In installation shafts, space is limited and access to the wall is difficult. In such cases, it is advisable to use longer brackets (for mounting multiple pipes at once) with one common fixed point. Scheme: one massive bracket anchored into the side of the shaft carries the entire pipe assembly, with one pipe fixed on the bracket and the others sliding. This solution saves time and material, but requires a precise calculation of directional expansion.

Choosing a bracket or strap for a fixed point – practical recommendations

For diameters 15–18 mm, the range primarily includes two variants of fixing brackets, which differ not only in dimensions but also in construction:

Single-sided bracket – simple and quick installation, the pipe is inserted from the side. Suitable for sliding and fixed mounting, a fixed effect is achieved by tightening firmly and adding an axial stop (ring on the pipe).
Two-piece bracket (bottom + top) – stronger pipe grip, better hold, recommended where the fixed point is exposed to higher forces (e.g., at a direct bend or with heavier fittings).

For a pipe of exactly 16 mm (standard PB pipe), choose the 16 mm bracket. For a combination of 16–18 mm diameters or if you are unsure of the exact dimensions, the more flexible option is the 16–18 mm bracket – it handles both diameters with sufficient clamping effect.

Tip from practice: if you are buying brackets for a longer route where fixed and sliding points will be mixed, I recommend using one type of bracket for the entire route and achieving the fixed point by adding a ring or stop on the pipe, not by switching to a different type of bracket. Unifying components makes later maintenance and possible repairs easier.

Dilation calculations for common scenarios – approximate values

The following table provides a practical idea of the dilation length for typical copper and PB pipe routes in a home installation (with a temperature difference of 50 °C, i.e., from 20 °C to 70 °C):

Material	Route length	Coefficient [mm/m/°C]	Extension at ΔT = 50 °C
Copper (Cu)	3 m	0.017	2.6 mm
Copper (Cu)	6 m	0.017	5.1 mm
Copper (Cu)	10 m	0.017	8.5 mm
PB plastic	3 m	0.13	19.5 mm
PB plastic	6 m	0.13	39.0 mm
PB plastic	10 m	0.13	65.0 mm

From the table it is clear why fixation is a much more critical issue for plastic pipes than for copper. While a 6 m copper route extends by just under 6 mm, a similarly long PB route extends by 39 mm – a difference that cannot be absorbed without a proper fixed point and compensator, risking damage to the installation.

Material compatibility and surface protection

When selecting fixing elements for a fixed point, do not forget about material compatibility. Copper and steel in contact with moisture form a galvanic cell, which accelerates corrosion of the copper pipe at the contact point. Therefore:

Brackets for copper pipe mounting should be made of stainless steel, non-rusting steel, or plastic.
If using steel brackets or consoles, insert a plastic or rubber strip between the pipe and the bracket (many brackets have this integrated).
For PB/PE pipes, galvanic corrosion is not an issue, but ensure that the bracket does not mechanically damage the softer surface of the plastic pipe during tightening.

In environments with higher humidity (boiler rooms, basements, shafts), also pay attention to the surface treatment of consoles and screws. Galvanization provides basic protection, but for more aggressive environments consider using non-rusting screws. KOMBI M8 screws from our range are suitable for standard indoor environments; for humid areas, verify the material type.

Most frequently asked questions (FAQ)

What is the difference between a fixed point and a sliding support – can I use the same brackets for both?

Yes, in principle you can use the same type of bracket for both purposes – the difference is not in the bracket type, but in the installation method and whether the pipe has axial clearance in the bracket. For sliding support, do not tighten the bracket fully and allow the pipe to move longitudinally. For a fixed point, tighten the bracket fully and secure the pipe with an axial stop (e.g., a ring slipped onto the pipe just next to the bracket). If the bracket does not have a mechanism to block axial movement, tightening alone is not sufficient – friction in the bracket can be overcome by higher forces.

How many fixed points do I need for a 10-meter section of PB pipe?

For a 10 m PB pipe with a 50 °C temperature swing, we are talking about an extension of 65 mm. A standard solution is one fixed point in the middle (5 m from each end) and one expansion compensator on each side of the fixed point – that is, 2.5 m from the end of the route. Each half of the route then extends by about 32 mm, which a standard compensator (an expansion elbow with arms of at least 400 mm) can easily absorb. Sliding supports should be placed every 0.7–1.0 m. If the route contains natural compensators (corner direction changes), one fixed point without additional supports may be sufficient.

What happens if I omit the fixed point entirely?

It depends on the material and the length of the route. For short copper sections (up to 2–3 m), the installation may function for years without a fixed point, as joints, elbows, and fittings absorb small expansions. For long routes, plastic pipe, or where adjacent fittings are sensitive to mechanical stress (thermostatic heads, control valves), a missing fixed point will cause material fatigue, loosening of joints, vibrations, and in the worst case, cracking of the joint or fitting. From a long-term perspective, an installation without a fixed point is a time bomb, the explosion of which depends only on the number of heating seasons.

Can I install a fixed point into a gypsum board partition?

Gypsum board by itself is not a suitable base for a fixed point – the load-bearing capacity of standard gypsum board anchors is too low to transfer expansion forces. If there is a wooden load-bearing structure behind the gypsum board (CW/UW profiles or wooden studs), you can screw the bracket directly into the profile or stud – this is an acceptable solution. If there is nothing behind the gypsum board, you must either embed a solid block into the structure before closing the partition, or reroute the pipe so that the fixed point is directed toward a masonry wall.

What is the maximum spacing between sliding supports between two fixed points?

Normative values for support spacing vary according to material and pipe diameter. For Cu 15–18 mm: vertical routing max. 2.0 m, horizontal max. 1.5–2.0 m. For PB/PE 15–18 mm: vertical max. 1.0–1.2 m, horizontal max. 0.7–1.0 m. Plastic pipe requires denser support, as it is softer and loses rigidity at higher temperatures (so-called plastic flow). Pipe manufacturers specify exact values in technical documentation – always follow them rather than general recommendations.

How do I know if the fixed point is not working properly – what are the symptoms?

The first symptom is usually noise – clicking, cracking or tapping of the pipe during heating and cooling. This means that the pipe is moving where

Do you have a question about this topic?

Not sure or dealing with a specific situation in your home? Write to us – we are happy to help.