Step-by-step installation of mounting elements for expansion tanks and plumbing

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Installation of Mounting Elements for Expansion Tanks and Sanitary Fixtures Step by Step

Proper installation of mounting and connecting elements is the foundation of every reliable plumbing installation. Whether you are mounting an expansion tank in a boiler room, connecting sanitary fixtures in a bathroom, or solving hot water distribution – each connection, each bracket, and each screw must be installed in such a way that it can withstand not only static load, but also pressure, vibrations, and temperature changes over many years of operation. From practice, I know that it is precisely during the installation of "small details" – that is, connecting and mounting elements – that the most mistakes are made. And these mistakes are usually revealed only when there is a leak, when the tank falls off the wall, or when the connection tears during the first pressurization of the system.

This article will guide you through the entire installation process step by step: from preparing the base, through selecting the right materials, to the final inspection and pressure test. We will focus mainly on the installation of expansion tanks and sanitary fixtures, as these applications are most common in practice and at the same time most prone to errors.

Why proper installation of mounting elements is so important

An expansion tank is not just a device that "hangs on the wall". When heating the heating water, the system operates with pressures typically in the range of 1.5 to 3.0 bar, and in the case of a failure of the safety valve, the pressure can temporarily reach 4–6 bar. This load is directly transferred to the mounting element in the wall and to the threaded connection of the tank with the piping. If the installation is poor – the thread is damaged, the seal is applied incorrectly, the bracket is mounted in a hollow brick without an anchor – the consequences can be catastrophic. Not only will you lose the device, but in the worst case, water will leak into the wall or the entire heating system will fail.

In the case of sanitary fixtures – sinks, bidets, WC cisterns – the situation is similar. A poorly mounted bracket will not withstand the load, a poorly sealed water supply will leak and in the long term cause moisture, mold, and damage to the building structure. From dozens of customer orders, I know that the most common reason for complaints after the installation of sanitary fixtures is not a product defect, but an installation error.

Tools and materials you will need

Before you start, have everything within reach. Interrupted work, where you constantly run for tools, increases the risk of errors.

Hammer drill or chiseling drill (for masonry and concrete)
Set of masonry drill bits with diameters of 8, 10 and 12 mm
Water level (min. 40 cm, ideally 60 cm)
Tape measure, pencil, plumb bob
Torque wrench (important for threaded connections!)
Adjustable wrench or wrenches #24, 27, 30
Sealing tape (PTFE tape, min. 12 mm width)
Gaskets suitable for potable and heating water systems
Chemical anchor or expansion anchors according to the type of base
Silicone sealant for sanitary applications (neutral, not acetic)
Mounting kit M8 for M8 threaded connections
Mounting set for expansion tank 3/4"

I especially emphasize the torque wrench – in practice, many installers skip it and rely on "hand feel". With plastic threads and brass fittings, this is a fatal mistake. An over-tightened M8 thread in a sanitary fitting cannot be repaired on site when it breaks and the entire fitting must be replaced.

Step 1 – Preparation and positioning

The first step is just as important as the installation itself – and it is precisely here that the most mistakes are made. Before drilling any hole, you must know exactly where the pipes will run, where the electrical installations are, and where the load-bearing elements of the structure are. For this, a metal and electrical installation detector is used – cheap, but invaluable in practice. I have seen cases where an installer drilled directly into an electrical cable simply because he "assumed" the cable ran elsewhere.

For expansion tanks, the following basic positioning rules apply:

The tank must be mounted so that the connection (usually a 3/4" thread) points downward or to the side – never upward, because the air in the tank would not be able to distribute properly
Minimum distance from other devices: 100 mm on each side (for access during maintenance)
Installation height: the tank connection must be accessible without a ladder – ideally 1.2 to 1.6 m from the floor
The wall must be load-bearing – a hollow drywall partition is not a suitable base for an expansion tank over 8 liters without special anchoring systems

For sanitary fixtures (sinks, WC cisterns, bidets), always check the height codes according to the STN EN 31 standard. The standard height of the top edge of the sink is 800–850 mm, WC seat 400–420 mm. A deviation greater than 20 mm will be disturbing even in use.

Mark the position carefully with a pencil. Use a water level – visual inspection "by eye" is not sufficient, especially for brackets, where even a 2° deviation will cause a visible tilt of the device.

Step 2 – Drilling and preparing the holes

The type of drill bit and hole diameter are selected according to the anchor and load. For expansion tanks up to 18 liters, 10 mm anchors are usually sufficient, for larger tanks (35–50 l) I recommend 12 mm. Always drill 1 mm larger diameter than the manufacturer specifies for the anchor – in practice, masonry is uneven and a 1 mm larger hole allows for a clean installation of the anchor without forcing it in.

Drilling procedure:

Set the drilling depth: use the drill rod scale or a depth stop. The hole must be at least 10 mm deeper than the anchor's working length
Drill perpendicular to the wall – a slanted hole will prevent proper expansion of the sleeve anchor
Clean the hole thoroughly after drilling – blow it out with compressed air or vacuum. Dust and mortar particles reduce friction forces and the load-bearing capacity of the anchor can drop by up to 30 %
For chemical anchors: the hole must be dry and free of dust – a dusty hole will prevent the chemical anchor from achieving its designed load capacity

Step 3 – Mounting the bracket and fixing plate

After drilling and cleaning the holes, it is time to install the bracket or fixing plate itself. For mounting expansion tanks, either a direct bracket (welded or bolted to the tank) or a separate flange with a collar is most commonly used. For smaller tanks up to 25 liters, a single anchoring point is typically used in combination with a hanging bracket and side stabilizers.

The specific procedure for installing the expansion tank fixing set 3/4":

Insert the anchor into the hole – it should go in by hand or with a gentle tap from a rubber mallet. If you have to hit it hard, the hole is too narrow – do not force the anchor in, as it will expand prematurely
Position the bracket in the correct location. Check the level once again – this is the easiest time to make corrections
Insert the screws through the bracket holes into the anchors. Tighten by hand until the bracket sits firmly against the wall
Final tightening with a torque wrench. For M8 screws, the recommended tightening torque is 18–22 Nm for steel, 12–15 Nm for brass. Never exceed these values – over-tightening will damage the anchor thread or deform the bracket
After tightening, check that the bracket does not "flex" – that is, there is no gap between the bracket and the wall. If there is, check the hole depth and replace the unsuitable anchor with a longer one

When working with the mounting bracket M8, it is important to ensure the threaded part is properly secured. The M8 bracket is used as a connecting and anchoring element – its function is to transfer the load from the tank to the wall structure. The M8 thread has a pitch of 1.25 mm and the load capacity of the threaded connection depends on the depth of the thread engagement – the minimum engaged thread length should be 1.5× the diameter, i.e., at least 12 mm for M8.

Step 4 – Connecting the piping to the expansion tank

Connecting the tank to the piping is equally critical. The most common connection is a 3/4" external thread (tank) and a 3/4" internal thread (pipe fitting). Sealing procedure for the threaded connection:

PTFE tape: Wrap 5–7 layers in the direction of the thread (clockwise when looking at the end of the thread). Start from the second thread, not the very end. The tape must be wrapped tightly, without air bubbles
Liquid sealant: For pressures above 3 bar or for hot water, I recommend combining PTFE tape with liquid sealant. Apply a thin layer on the external thread after wrapping the tape
Screwing in: Start by hand – the fitting must go in easily at least 2–3 threads. If it is difficult from the start, the thread is not properly aligned and there is a risk of cutting it
Tightening with a wrench: For a 3/4" fitting, use a wrench size 27 (opposite wrench opening). Torque: 30–40 Nm. The tank handle must be supported with the other hand or with an opposite wrench during tightening – you do not want the rotational force to be transferred to the membrane inside the tank

Step 5 – Installation of sanitary fixtures: basins, bidets, toilets

Sanitary fixtures have their own specifics. Bath ceramic is heavy and brittle at the same time – a basin typically weighs 15–25 kg, a toilet cistern with water another 10–15 kg. On the other hand, ceramic does not tolerate shocks and overloading of point cantilevers. Therefore, when installing cantilevers for basins, the rule applies: a larger anchoring element is better than a smaller one, and a glued joint (chemical anchor) is better than mechanical anchors in old walls.

Procedure for installing cantilever basins:

Align the position of the cantilevers according to the spacing specified by the manufacturer (typically 200–250 mm center-to-center)
Drill holes, insert anchors or chemical anchors
Mount the cantilevers: tighten the screws with a minimum torque of 15 Nm for thread M8
Mount the basin on the cantilevers – check with a spirit level
Trap and drain: lubricate the rubber seal with glycerin (not WD-40!) before tightening. An over-tightened PVC trap will tear
Water supply: tighten the flexible hose with a wrench, not by hand. Torque 8–10 Nm for 3/8" connection
Sealant: apply neutral sanitary silicone, not acetic silicone, at the basin-wall junction (acetic silicone can damage some surface finishes of fittings)

For suspended toilets with a hidden cistern (pre-wall systems), a completely different methodology applies – here the mounting frame is anchored into the floor and wall with chemical anchors according to the manufacturer's static assessment. The frame's load-bearing capacity must normally withstand 400 kg of dynamic load (standard EN 997).

Step 6 – Sealing of connections and preventing water leaks

Sealing is a topic where mistakes are not made out of ignorance, but out of laziness and haste. I have seen dozens of jobs where the installer "saved" 2 minutes on sealing and the customer then paid thousands to repair the wet wall. Let's go through the main types of sealing materials and where to use them:

PTFE tape (Teflon tape): The most universal material for metal threads DN 15 to DN 50 (3/8" to 2"). Wrap at least 5 layers, for hot water above 80°C I recommend 8–10 layers. The tape must not be twisted – when tightening the fitting, check that the tape does not start to separate.

Hemp rope + sealant: A traditional method, still reliable for threads up to 1". The rope is wound in the direction of the thread, then filled with a paste sealant (e.g. Fermit, Unipak). Advantage: the rope slightly expands when wet and the joint "self-seals". Not suitable for stainless steel threads – the rope can cause corrosion.

Rubber O-rings and flat seals: For flanged joints and threaded connections with a seating surface (e.g. flexible hoses). The seal must never be placed on the thread – it belongs on the seating surface. The rubber must be resistant to the medium: for hot water and heating equipment, use EPDM (resistance up to 140°C), not NBR (max. 90°C for water).

Liquid sealants: For joints where vibration occurs (pumps, heat exchangers), a combination of PTFE tape and liquid sealant is recommended. Anaerobic adhesive-based liquid sealants (e.g. Loctite 577) are suitable for metal threads up to 2", resistant to 150°C. Note: these sealants partially fix the joint – disassembly requires heating the joint with a flame.

Step 7 – Pressure test and final inspection

After the installation is completed, a mandatory pressure test follows. For heating systems with an expansion tank, the standard STN EN 14336 applies, for sanitary installations STN EN 806-4. The pressure test is performed with water (not air – air in case of a broken joint poses a risk to health and safety).

Procedure for the pressure test:

Fill the system with water and bleed all branches and devices
Set the test pressure with a manometer: for heating systems 1.5× operating pressure, min. 6 bar. For sanitary systems usually 1.1× max. operating pressure, min. 11 bar
Let the pressure act for at least 30 minutes (for heating systems) or 60 minutes (for sanitary systems)
A pressure drop of no more than 0.2 bar in 30 minutes is acceptable due to thermal compensation. A larger drop indicates a leak
Visually inspect every joint – with your hand or a paper shadow. A wet joint is immediately visible

If the pressure holds, perform a functional test: turn on the heating system, wait for the operating temperature to be reached (min. 60°C) and check all joints again. Temperature changes the dimensions of metal parts and some joints that seal when cold may leak when hot (and vice versa).

Common mistakes from practice and how to avoid them

After years of experience in the field, I have compiled a list of the most common mistakes I repeatedly see:

Installation into hollow material: Anchors into hollow ceramic or hollow bricks without special hollow anchors – the cantilever pulls out after loading. Always identify the type of substrate before you start drilling
Insufficient thread depth: M8 thread with engaged length only 6–8 mm in soft substrate (gypsum, aerated concrete) – the screw pulls out on the first dynamic load
Over-tightened fitting thread: Installer tightens "as tight as possible" without a torque wrench, the brass fitting thread or plastic valve body cracks
Wrong direction of PTFE tape winding: Tape wound in the opposite direction unwinds during tightening and the joint does not seal
Undepressurized expansion tank: Membrane pre-tension is not set before filling the system with water (standard 1.0–1.5 bar nitrogen) – the tank then does not work properly and the system suffers from water hammer
Unsupported cantilever during installation: When tightening the tank connection to the pipe, the tank freely rotates and deforms the membrane or damages the cantilever

Learn more about these scenarios in the article Common mistakes when installing connecting elements in the bathroom and how to avoid them directly in our Knowledge Center.

Specific situations: old housing stock and renovations

Renovations of older apartments (1960–1985) bring particular challenges. The original masonry is often made of hollow bricks or materials with unknown load-bearing capacity. Old galvanized steel pipes have corroded threads that crack during dismantling.

Recommended procedure for renovations:

Always test the load-bearing capacity of existing brackets before installing new equipment – hang a load 2× greater than planned and observe the behavior
For old threads: apply WD-40 or penetrating oil at least 2 hours before dismantling. Never use brute force – rather cut the pipe and install a new connection
Chemical anchors are significantly more reliable than mechanical anchors in old masonry
Always check the condition of existing insulation on the pipes – renovation is an ideal opportunity to renew it

If you are unsure about choosing the right fastening system for a specific type of base material, I recommend reading our article Comparison of types of fastening systems for plumbing and How to choose the right connecting and fastening elements for the bathroom and sanitation in this Knowledge Center.

Dimensional overviews and technical parameters

For quick orientation when selecting the correct fastening elements, I present an overview table of the most commonly used dimensions in plumbing and heating installations:

Device	Connection thread	Bracket thread	Tightening torque (Nm)	Sealing
Expansion tank up to 25 l	3/4" BSP	M8	30–40	PTFE 7 layers
Expansion tank 25–50 l	1" BSP	M10	50–60	PTFE + gasket
Basin (water supply)	3/8" BSP	M8	8–12	Flat rubber (EPDM)
Toilet cistern (supply)	3/8" BSP	M6	5–8	Flat rubber
Shower set	1/2" BSP	M8	15–20	PTFE 5 layers
Safety valve	1/2" – 3/4" BSP	—	25–35	PTFE + gasket

If you need a deeper analysis of thread selection, see the article Thread M8 vs. other sizes: what mounting kit do I need or What thread and connection diameter to choose for an expansion tank in this Knowledge Center.

Maintenance and long-term reliability of fastening elements

Installation is not a one-time task, but a part of long-term care for the installation. Fastening elements must be regularly checked, especially in environments with higher temperatures, humidity, and vibrations.

Recommended inspection schedule:

After each heating season (once a year): Visual inspection of expansion tank brackets, check the tightness of the connection, check the pre-tension of the membrane (using a manometer on the air valve of the tank – typically 1.0–1.5 bar)
Every 2 years: Check the tightening torque of the bracket screws (a drop of more than 20 % indicates loosening or corrosion of the thread)
Every 5 years: Replace rubber seals in plumbing connections, check the condition of PTFE seals on visible threads
After any water leak: Immediate disassembly, cleaning, seal replacement and reassembly – never reconnect a loosened joint without disassembly

A more detailed look at preventive maintenance can be found in the article Maintenance and inspection of fastening elements in plumbing installations in this Knowledge Center.

Most frequently asked questions (FAQ)

What is the difference between an expansion tank bracket and a regular tool bracket?

An expansion tank bracket must withstand combined loading: the static weight of the tank (up to 30–50 kg for larger types), pressure pulses in the system (vibrations from the pump), and dynamic loading during service, when the plumber holds the tank in one hand. Regular brackets (e.g., shelf brackets) are dimensioned only for static loading and do not have the corresponding thread interface for gas connections. Never use non-certified brackets for pressure equipment – in the event of a failure, the plumber is responsible.

Do I need to use a special kit when installing an expansion tank, or are regular anchors from the store sufficient?

For small tanks up to 8 liters (e.g., pressure tanks for well pumps), high-quality nylon anchors with a diameter of 10 mm and an M8 screw in solid masonry may be sufficient. For tanks over 18 liters, I strongly recommend using a complete expansion tank mounting kit 3/4", which is specifically designed for this purpose – it has a properly dimensioned bracket, a connection with a seal, and all anchoring elements. An improvised installation using various parts may work, but in the event of a failure, you are in a legal vacuum.

Can I use an M8 mounting bracket for larger devices or only for expansion tanks?

Mounting bracket M8 is a universal fastening element for metric thread M8, so it can be used wherever it is necessary to connect or anchor a device with this thread – basin brackets, pipe fastening, installation of plumbing brackets. The limiting factor is the maximum load capacity of the M8 thread in the given material (masonry, concrete) and the maximum tightening torque (18–22 Nm for steel). For higher loads (hanging toilets, room dividers), it is necessary to use thread M10 or M12.

Why is my connection leaking, even though I sealed it thoroughly with PTFE tape?

The most common causes are: the tape is wound in the wrong direction (it unwinds during tightening), insufficient number of layers (less than 5), the connection was contaminated with grease or dirt before sealing, or the thread is mechanically damaged (e.g., the first thread is deformed by previous forceful tightening). A more detailed solution is described in the article Why is the connection leaking at the expansion tank: causes and solutions.

What pre-charge (pressure) should the air chamber of the expansion tank have before installation?

The pre-charge of the air chamber must correspond to the lowest pressure at the installation location of the tank – typically the static pressure at the lowest point of the system. For a standard family house, this is 1.0–1.5 bar. Always check the pre-charge before filling the system with water: drain all water from the system, remove the tank connection, and measure with a pressure gauge on the air valve (Schrader valve, the same as on a bicycle tire). If the pre-charge is low, add nitrogen or air using a compressor. Never change the pre-charge when the tank is filled – you won't be able to tell whether you're measuring air or water.

What to do if the bracket slightly "creaks" after installation (is not firmly fixed in the wall)?

If the bracket still shows some play after fully tightening the screws, there are two possible causes: the hole is too large (the anchor cannot expand properly) or the wall material is too soft (lightweight concrete, plaster). Solution: remove the anchor, fill the hole with chemical adhesive, drill a new hole into the hardened chemical adhesive after it has cured (minimum 30 minutes), and insert the screw. This solution works in plaster and lightweight concrete as well. Never compensate for bracket play by tightening with a higher torque – you will damage the anchors.

Conclusion: Why it pays off to do the installation thoroughly from the very beginning

The entire process may seem time-consuming, but in practice, an experienced plumber can install an expansion tank, including anchoring and connection, in 45–90 minutes. The same job done hastily and with errors can cost the customer repeated site visits, wall repairs, and in the worst case, compensation for damage. Quality connecting and fastening systems are the foundation of a safe and long-term reliable installation.

Remember: in plumbing and heating technology, there is no such thing as "good enough" fastening. There is only correctly dimensioned, properly installed, and properly sealed fastening – or a failure that will occur sooner or later. Investment in the right tools, right materials, and thorough installation always pays off.

Do you have a question about this topic?

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