Common mistakes during installation of connecting parts in the bathroom and how to avoid them
Common mistakes when installing connecting elements in the bathroom and how to avoid them
Over the years of experience in plumbing installations, I have seen dozens of cases where a customer called to say that their connection was leaking, the thread was loose, or after a few months the entire radiator had detached from the wall. In most cases, the cause was not poor material quality – it was an installation error. Sometimes a small one, sometimes a major one. I wrote this article so that you can recognize these mistakes, avoid them, and possibly even fix them if they have already occurred.
The bathroom is an environment where connecting and fastening elements are exposed to a combination of humidity, temperature changes, vibrations, and chemical influences (cleaning agents, air saturated with steam). This means that any installation error will manifest itself much faster and more dramatically here than, for example, in a dry technical room. That is why it is important to understand not only what is being installed, but also why it is being installed in exactly that way.
1. Wrong choice of connecting element – the foundation of all problems
The first and most common mistake starts even before the actual installation: the customer (or an inexperienced plumber) reaches for what is available at hand, not for what actually fits. In practice, this looks like using a sealing ring designed for 1/2 inch on a 3/4 inch threaded connection, or using M10 screws in M8 holes with the excuse that "they are a bit loose, but it will work". It won't.
Each connecting element has precisely defined parameters: thread diameter, thread pitch, material, surface treatment, and resistance to the medium (water, steam, heat transfer fluid). If even one of these parameters does not match, the connection either does not work at all or works for a while and then fails – which is actually more dangerous.
A good example from practice is a situation where a customer bought a mounting bracket M8 and wanted to use it to mount a body with an M10 hole, because M8 was cheaper and in stock. The result: after three months, the entire body became loose, because there was a gap in the hole and water with corrosion made a home there. A seemingly small 2 mm difference in thread diameter can have very specific and costly consequences.
You will read more about how to distinguish between different dimensions and types of threads in the article Thread M8 vs. other dimensions: which mounting bracket do I need, where you will also find tables for quick comparison.
2. Underestimating wall anchoring – the most common source of failure
The second major category of errors concerns the actual anchoring into the building structure. A bathroom wall can be masonry, drywall, made of aerated concrete, solid or hollow bricks, and covered with ceramic tiles... and for each type of base, there are different rules for anchoring. Ignoring these rules causes anchors and screws to loosen over time.
Wall anchors – the most common mistake in practice
The first mistake: using a classic plastic anchor S6 or S8 in drywall. These anchors are intended for solid substrates (concrete, solid brick, hollow brick with appropriate anchors). In drywall or in hollow blocks, special anchors must be used – butterfly anchors, self-tapping anchors, or metal expanding anchors for hollow substrates. When this is ignored, the wall holds well for the first year, but at the first sudden movement (a child hanging on a towel ladder, someone leaning their full weight on the sink), the entire system pulls out.
The second mistake: drilling without considering the position of the reinforcing profiles in drywall. A properly placed anchor in a CW or UW profile can withstand significantly higher loads than an anchor placed between the profiles just into the board itself.
The third mistake: drilling into the grout line instead of into the tile itself. Drilling into the grout line is easier (grout is soft), but the anchor has almost no load-bearing capacity there and after some time it causes cracking of the grout line and loosening of the tile around it.
Preliminary marking and measurement
Another problem: installation "by eye". In the bathroom, the rule applies: measure twice, drill once. The spacing of the mounting points must correspond to the manufacturer-specified spacing for the given sanitary fixture. For example, if a pedestal sink requires a mounting bracket with a 120 mm spacing and you drill the holes at 110 mm, you will either not be able to install the fixture at all or you will force it on, causing microcracks in the ceramic – these may not be immediately visible, but they will fully manifest at the first pressure surge.
3. Sealing – where water leakage begins and ends
Sealing is a topic where the most mistakes are made. Paradoxically – most people think they know how to seal. "I'll wrap the hemp, tighten it, and that's it." Reality is more complicated.
The type of sealing must match the application
For threaded connections in cold water distribution, Teflon tape (PTFE tape), hemp fiber with Hermatite or rubber sealing rings are commonly used. Each of these materials has its place and conditions of use:
- PTFE tape – suitable for most threaded connections of cold and hot water, gas (special yellow version), not suitable for connections that will be repeatedly disassembled and reassembled in the future (loses elasticity)
- Hemp fiber with paste – traditional method, still functional, requires experience with the amount of material; too little = leakage, too much = thread jammed
- Rubber seal / O-ring – used for flat sealing connections (flanges, heads), never for threaded connections, where the seal is pressed into the thread
- Liquid sealant – modern solution for combination with PTFE or alone, suitable also for plastic threads, where there is a risk of tearing due to over-tightening
Typical mistake from practice: a customer used standard white PTFE tape on a heating radiator connection, where the temperature reaches 70–80 °C. Standard white PTFE tape is indeed heat-resistant, but if it is not wound correctly (in the direction of the thread and with sufficient number of layers), the connection will loosen due to thermal expansion. Here, you should use either a special reinforced sealing tape or a combination of hemp fiber and heating paste.
Direction of PTFE tape winding
It sounds trivial, but it is a real source of problems: PTFE tape must be wound in the direction of the thread (in the direction in which you will tighten the connection). If it is wound in the opposite direction, it will roll off during tightening and the connection will not seal. Correct procedure: hold the end of the tape with your finger at the beginning of the thread and wind the tape so that, when viewed from above the thread, it is wound clockwise (for a right-hand thread).
4. Over-tightening or under-tightening of connecting elements
"The tighter I tighten, the better the seal" – this belief causes a huge amount of damage. In reality, it works exactly the opposite: over-tightening causes deformation of the seal, cracking of ceramic or plastic, and cutting of the thread. The result is that the connection leaks or breaks – and in the worst case directly during installation, in the best case (paradoxically) a week later.
Tightening torque – why it is important
For standard household installations, approximate tightening torque values apply. For example, for chrome-plated mounting screws M8 in sanitary technology, the recommended torque ranges from 8–12 Nm. For brass or stainless steel threads, it may be different. Professional installers use torque wrenches – amateurs "feel the torque by hand". The hand is a good tool, but without reference experience, it is easy to over-tighten.
For plastic threads (e.g. PEX or PPR connections), an even stricter rule applies: never tighten more than the manufacturer specifies. Plastic will give way, but a microcrack that forms will appear months later.
Under-tightening
On the other hand, an under-tightened connection leaks immediately or at the first pressure increase. The danger here is especially high with expansion tanks, where a sudden pressure rise (water hammer, failed safety valve) can cause an under-tightened connection to break. More on this topic can be found in the article Why the connection leaks at the expansion tank: causes and solutions.
5. Errors in mounting expansion tanks
The expansion tank is a component that most people underestimate precisely because it "hangs in the corner of the technical room and does nothing". In reality, it is a device that works under pressure, carries its own weight (up to 10–30 kg or more when fully filled), and must withstand vibrations from the circulation pump. Therefore, the mounting must correspond to this load.
When installing an expansion tank, it is recommended to use a complete expansion tank mounting set 3/4", which contains all the necessary components designed for cooperation – bracket, securing strap, appropriate screws. Improvisation with various parts from different sources is really not a good idea here.
Typical errors in expansion tank installation
- Incorrect hanging height – the tank must be placed so that the filling and draining valve is accessible. Too low or too high can prevent servicing.
- Insufficiently dimensioned bracket – the bracket must carry the full weight of the tank. For tanks over 12 liters, a two-point bracket anchoring is recommended.
- Connection in the wrong direction or thread type – the most common problem: the customer buys a set with a 3/4" thread, but the tank has a 1/2" connection or vice versa. Always check the type of connection on the tank label before purchase. A more detailed description of choosing the correct connection can be found in the article What thread and diameter to choose for the expansion tank.
- Connection seal not renewed before reinstallation – if the tank is disassembled for membrane replacement, the old PTFE tape on the thread must be completely removed and the thread must be resealed. Many people skip this step and the result is obvious.
- Placing the tank in a freezing area – the expansion tank must not be placed in an area where freezing is a risk. Freezing of the expanding liquid will destroy the membrane.
The complete installation procedure including the order of steps can be found in the article Installation of fasteners for expansion tanks and sanitary fixtures step by step.
6. Corrosion and galvanic corrosion – the silent enemy
Another area that is often underestimated by amateur plumbers (and sometimes even by professionals) is galvanic corrosion. It occurs when two different metals are in direct contact in the presence of an electrolyte (water). In a bathroom, this electrolyte is always present.
Classic mistake: a steel screw in a brass body. Brass is a more noble metal than regular steel, so the steel corrodes preferentially. After one or two years, the screw is practically unusable, the head breaks off when trying to unscrew it, and the entire joint must be chiseled out or drilled out. Correct solution: always use screws and fastening elements made of the same or compatible material – stainless steel (A2 or A4) is almost always the right choice in a bathroom. Brass elements with brass screws. Plastic consoles with galvanized screws only if they are not in contact with water.
Another problem: the use of standard galvanized screws and wall anchors in a permanently damp environment (shower, steam sauna). Galvanization in such an environment lasts 1–3 years, then it starts to flake off and the screws rust. Color stains from rust on white tiles are not only an aesthetic issue – they indicate that the joint is losing strength.
7. Installation without professional planning – "I'll do it myself" and its consequences
DIY (do-it-yourself) installations are becoming increasingly popular, and that is fine – many tasks in a bathroom can be handled by a skilled handyman. However, there are situations where you cannot do without a professional or at least without thorough preparation:
- Any installation connected to the pressurized water supply (building regulations law, or possibly insurance requirements)
- Mounting sanitary fixtures into load-bearing structures (e.g., a suspended toilet into an installation wall)
- Work on central heating systems including the expansion tank
- Installations in older apartments with unknown wall structures and pipe layouts
We have dealt with a situation in practice where a customer installed a toilet on drywall himself, but did not realize that behind the tiling was a gypsum board on a steel frame, not masonry. He used standard S8 wall anchors, the toilet stood fine for a year, then under greater mechanical stress the entire assembly was pulled out of the wall along with the tiling. The damage exceeded 2000 euros.
8. Mistakes in the use of installation jigs and special tools
An installation jig is not just a "helper rod". A properly dimensioned and used jig ensures accurate positioning, correct depth of embedding, and the correct angle. If you use it incorrectly – or if you don't use it at all – difficulties may arise that cannot be easily resolved later.
Installation jig M8 is used for precise guidance when drilling and installing M8 threaded elements. Its use is especially important when installing into tiled surfaces, where a millimeter deviation means a broken tile or a crooked joint. Without this jig, many people "guess" the position and end up with two or three unnecessary holes in expensive stone or ceramic tiles.
Another mistake: using a hammer drill when drilling through ceramic. The hammer function must always be turned off when drilling tiles – the vibration from the hammer causes the tile to crack (even if it is not immediately visible, the crack spreads under the surface). Correct procedure: diamond drill bit, no hammer function, slow speed, water cooling.
9. Wrong choice of material for the connecting element for a given application
The material of connecting elements is a key parameter that is easily underestimated in a bathroom. The classification is simple, but in practice it is often mixed up:
- Stainless steel A2 (AISI 304) – suitable for most bathroom applications, not suitable for environments with seawater or high chlorine content
- Stainless steel A4 (AISI 316) – more resistant, suitable even for chlorinated environments, steam showers, whirlpool systems
- Brass (CW617N and similar) – traditional material for sanitary fittings, excellent resistance, but sensitive to disinfectant solutions with higher chlorine content
- Plastic connecting elements (PA6, PP, POM) – suitable for light suspended systems, low-voltage applications, not suitable for high temperatures (above 60 °C) and mechanical stress
- Galvanized steel – acceptable only in dry areas or behind tiling, where it is not in contact with water
A more detailed comparison of materials and types of fastening systems for plumbing can be found in the article Comparison of types of fastening systems for plumbing.
10. Neglecting inspection after installation and during operation
The installation of connecting elements is not a one-time action. Proper professional work also includes the first test operation and inspection after a few days. In practice, a so-called "first seasonal inspection" is carried out – after the first full operation of the system, all connections are visually and manually checked (wet or cold surfaces indicate a leak).
Long-term maintenance of fastening elements should include: annual visual inspection of visible connections, checking the tightening of the expansion tank connection every 2 years, and checking the condition of the sealing during every disassembly. For more information on what and when to inspect, see the article Maintenance and inspection of fastening elements in plumbing installations.
One specific example from practice: a customer had beautiful chrome-plated towel racks in the bathroom, installed four years ago. During a routine inspection before renovation, we found that three out of four fastening points were almost loose – the screws had loosened on their own due to vibration (from adjacent washing machines, fan operation). No leak occurred only because the load was relatively low. If someone had hung an additional heavy wet towel, the entire system would have detached.
Most frequently asked questions (FAQ)
Can I use regular steel screws in the bathroom if I paint them with varnish?
This is not a good solution and does not work in the long term. Varnish on the threaded part of the screw does not last – it peels off when tightened and the metal remains unprotected. Moisture will find its way and corrosion will start. Always use screws made of stainless steel (A2 or A4) or brass, which are suitable for a wet environment without additional protection.
How can I tell that the thread sealing is no longer sealing?
The first sign is usually visible moisture or dripping at the connection point. A less obvious sign is a white lime coating around the connection (mineral deposit after water evaporation) or condensation drops in an uncontrolled position. If you suspect a leak, dry the connection completely with paper towels and monitor it for several hours – even a micro-leak will show up. The causes and solutions for leaks at the expansion tank connection are thoroughly discussed in the article Why the connection at the expansion tank is leaking: causes and solutions.
What is the difference between a plug for a solid brick and a hollow brick, and how can I tell?
Plugs for solid bricks (classic plastic S6, S8, S10) expand and grip when the screw is tightened into a solid material. For hollow bricks or drywall, you must use plugs that expand behind the hollow surface and create a grip on the back side of the wall (butterfly anchor, toggler, self-tapping anchor for drywall). You can easily determine the type of base material by tapping the wall – solid masonry gives a dull sound, while hollow material resonates. If you are unsure, drill a small test hole and use a probe to check the thickness and material.
Can I reuse PTFE tape on a connection that I disassemble and reassemble?
PTFE tape is not intended for repeated use. Each time you disassemble, you must completely remove the old tape, clean the thread, and apply new tape. If you expect that the connection will need to be disassembled in the future (e.g., a service connection for an expansion tank), consider using liquid sealant or a special sealing paste that can be cleaned and reapplied more easily.
Is it dangerous to leave a loose connection for a while before repairing it?
It depends on the situation, but generally speaking: every leak, even seemingly negligible, is a problem that gets worse. Moisture damages the structure, causes corrosion, reduces thermal insulation, and can lead to mold growth. A micro-leak at a pressure connection (heating, water supply) can turn into a larger rupture at any time – for example, during a water hammer or rapid pump start. Always repair it as soon as possible.
What to do if the thread in the body of the fitting is stripped and the screw just spins without grip?
If the body is made of brass or metal, there are options: a thread insert (helicoil insert) can restore the original thread, or a larger thread can be used with pre-drilling. If the body is plastic, the repair is more difficult – usually the entire part must be replaced. Therefore, it is important not to over-tighten threads in plastic fittings. Always check the condition of the thread before installation – the screw should manually go in at least 3 turns without resistance.
Conclusion: Prevention is always cheaper than repair
Every mistake in the installation of connecting elements in the bathroom has one common denominator: it could have been avoided. Either by choosing the right material and size, following the correct installation procedure, or simply by a bit of patience and planning before the actual work. The bathroom is a space where installations must last for many years without problems – and this can only be achieved if connecting and fastening elements are chosen correctly, installed correctly, and regularly inspected.
If you are unsure about the correct product, thread size, or type of plug for your base material, also check other articles in this Knowledge Center: How to choose the right connecting and fastening elements for the bathroom and plumbing or Common questions about connecting and fastening systems for the bathroom and plumbing – you will find more specific answers and practical tables there. Proper preparation before installation will save you time, money, and nerves.
Do you have a question about this topic?
Having trouble deciding or dealing with a specific situation in your home? Write to us – we are happy to help.