Common mistakes during installation of gas installation products and how to avoid them

Common mistakes during the installation of gas installation components and how to avoid them

Gas is a medium that heats water, cooks food, and heats homes for us every day. At the same time, it is a medium where one carelessness or one overlooked detail can end in a gas leak, explosion, or fire. Over the years of practice in this field, I have seen dozens of complaints, repair orders, and inspection findings that had a common denominator: the mistake did not occur at the gas appliance itself, but at small installation components – valves, hoses, fittings, seals. Precisely these are the most frequently underestimated.

This article is intended for installers, technically knowledgeable property owners, and anyone who wants to understand what happens during gas installation work and what to look for during inspection. We will not cover basic safety rules (such as not smoking or switching on switches during a gas leak) – these should be known by everyone. We focus on practical technical mistakes that even experienced plumbers make when working under time pressure, with the wrong materials, or due to inattention.

1. Incorrect selection of components – the foundation of everything

Use of water installation components in gas installation

This mistake is surprisingly common and at the same time one of the most dangerous. Many visually identical or very similar components exist in two versions: for water and for gas. At first glance, they look the same. Color, dimensions, threads – everything fits. But the seals, body material, surface treatment, and certification are completely different.

Specifically: a standard brass ball valve for water and ball valve for gas FF 2" internal thread/internal thread, with a lever may look almost identical, but the gas valve has a seal made of a material resistant to hydrocarbons (typically PTFE or special rubber), different requirements for sealing classes, and must be certified according to the EN 331 standard. A water installation valve does not meet these conditions. The rubber in the seat will break down over time and begin to leak. This may not be immediately visible – gas escapes slowly, without odor (if it is a small amount), but accumulates in a closed space.

The same problem applies to flexible hoses. A flexible hose for water and flexible connecting hose for gas WS-CE R1/2(T)-G1/2 MF 150cm differ in the material of the inner hose and in certification. A gas hose must be labeled for gas, must have the appropriate certification (e.g., CE), and must not be confused with water.

How to avoid this: Always check the product label or product description. Look for explicit labeling such as "for gas", "gas", or the appropriate standard (EN 331 for valves, EN 14800 for flexible hoses). If you are unsure, read our article Certificates and standards for gas installation components – what every part must have, where these requirements are discussed in detail.

Confusing threads and their pitfalls

Another classic mistake: the customer or installer buys a component with what appears to be the correct thread, but after installation, it leaks. The reason is the difference between the R thread (external conical – Whitworth conical BSPT) and the G thread (external cylindrical – Whitworth cylindrical BSPP). Both look the same at first glance and have the same numbering (e.g., 1/2"), but they are geometrically different. The conical thread seals itself, while the cylindrical thread requires a seal at the face (flat joint) or a seal on the thread.

In practice, it happens that the customer sees a "1/2" thread and buys anything with the same number. A flexible connecting hose has one side with R1/2(T) – i.e., a conical thread with a seal – and the other side with G1/2 – a cylindrical thread. If these interchangeable threads are combined incorrectly, the joint either cannot be tightened at all, or the seal is in the wrong position and leaks.

A detailed analysis of thread differences and sealing classes can be found in the article How to choose the correct gas ball valve – thread, material, and sealing class in this Knowledge Center.

2. Mistakes during the installation of flexible hoses

Too short or too long hose

A flexible hose must not be stretched like a string – this is a fairly well-known rule. Less is said about the opposite extreme: a hose that is too long, hanging in loops, tucked behind the appliance, or lying on the floor, is also problematic. It can be mechanically damaged (bent, broken at a point where the stainless steel braiding cracks and releases the corrugated tube), can be stepped on during cleaning, or can be positioned in such a way that it collects condensation.

The correct length of the hose should be such that it easily reaches from the fixed connection point to the appliance with a small reserve (typically 5–10 cm), but without excessive loops. When selecting, it is important to actually measure the route – not just estimate the distance by eye. A detailed measurement procedure can be found in the article What diameter and length of flexible gas hose – how to measure and choose correctly.

For longer distances, a suitable choice is, for example, Flexira xConnect Gas Standard R1/2(T)-G1/2, 2000 mm, which with a length of 2,000 mm covers even more spacious installations without the need to extend the route with rigid piping.

Torsional stress during installation

This is a technical mistake that you do not see at first glance, but the material "feels" it immediately. When tightening the hose into place, the installer naturally turns the body of the hose (not just the nut). This creates torsional (twisting) stress in the hose. The stainless steel braiding can withstand it, but the inner corrugated hose made of stainless steel can be unevenly stressed at the bends and, in the long term, leads to premature wear.

Correct procedure: hold the hose body in a neutral position and tighten using two wrenches – one to hold the opposite body (valve, gas cock on the stove), the other to tighten the nut. Never twist the entire hose.

Installation of flexible hose in vertical position without a valve

Flexible hoses are designed for flexible connection of an appliance to a fixed installation, not as part of a fixed piping system. The standard clearly states that the hose must be accessible and visible (must not pass through walls, floors or ceilings), and must be installed with a closing shut-off valve – that is, a ball valve or gas trap – on the side of the fixed installation. If the hose is installed without this valve (for example, directly from a rigid pipe to the appliance), in the case of the need to disconnect the appliance, you must close the main shut-off valve on the entire apartment installation.

Incorrect sealing of threaded connections

Threaded connections of flexible gas hoses must never be sealed with hemp and flax (flax fibers) – this is an old method valid for water, not for gas. The correct sealing of threads on a gas installation is PTFE tape (Teflon tape) or a special gas sealing compound (e.g. Fermit, Unipak Gas). These products are certified for gaseous media and are resistant to hydrocarbon fuels.

On the other hand, flat sealing at the end of the nut (e.g. on hoses with T-end) must not be sealed with tape or compound – the sealing is solved by a rubber or PTFE ring at the end of the nut and any additional sealing compound may damage the joint or prevent proper seating.

3. Errors in the installation of ball valves on gas

Over-tightening and deformation of the seat

Ball valves have PTFE seats in the body, on which the ball rests and seals. These seats are precisely dimensioned. If the fitter over-tightens the valve into the thread (or turns it in the flow direction instead of the correct direction), it may lead to deformation of the valve housing or distortion of the sealing surfaces. Result: the valve appears to function well, but after long-term use it starts to leak around the seat. This is especially insidious with larger diameters, for example with a 2-inch valve.

The correct installation procedure for a ball valve is described in detail in the article Installation of a ball valve on gas – procedure, tools and safety rules. Basic rule: always tighten the valve in the "closed" position (lever perpendicular to the flow axis) and do not exceed the recommended tightening torque according to the DN diameter.

Installation of the valve in the wrong position

Gas ball valves are mostly designed for installation in a horizontal pipe with the lever pointing upwards. Installation "upside down" (lever downwards) may in some constructions cause the ball to not be properly supported by the bearings and after long-term loading (ball weight + operating pressures) eccentric wear of the seals occurs.

Most modern gas ball valves are "multi-position" – that is, they can be mounted in any position. Always check the technical data sheet of the product to see if the specific valve allows this. If not stated otherwise in the documentation, install the valve with the lever upwards or sideways, not downwards.

Missing or incorrectly placed shut-off valve

According to current legislation and STN standards, each gas appliance must have its own shut-off valve – a cock or ball valve – located in the immediate vicinity of the appliance, accessible and visible. This shut-off valve is used to quickly disconnect the appliance without having to interfere with the rest of the installation.

In practice, it happens that during kitchen renovations stoves are moved, hose connections are extended, but the shut-off valve remains hidden behind the kitchen unit, inaccessible without pulling out the furniture. This is a direct violation of safety requirements and will be marked as a defect during inspection.

4. Sealing materials and their replacement

Using inappropriate sealing material

Everyone who has worked in plumbing for some time has various sealing tapes and gaskets in their toolbox. The problem arises when, in a rush, one grabs the first one available. On gas installations, a clear rule applies: use only sealing materials explicitly approved for gas (marked "Gas", "Gaz", or with the appropriate standard).

PTFE tape is generally accepted for threaded connections on gas pipes, but it must be wound correctly: in the direction of the thread, so that it winds up when tightening, not unwinds. The minimum number of tape layers for a gas connection is 3–4 layers (more than for water). Some tapes are specially thicker and designed directly for gas – these are more reliable.

Hemp fiber (flax) is absolutely unsuitable for gas – it degrades biologically, dries out, and shrinks with temperature changes. A connection that was tight for the first few months may start to leak after a year.

Missing or damaged sealing ring in the nut face

Flexible hoses with T-ends (conical nut with a distinct sealing surface) use a sealing ring in the nut face, either rubber or PTFE. This ring is part of the hose and must be checked before installation. If the ring is cracked, deformed, or missing, the connection will leak even after thorough tightening.

Common practice on construction sites: the hose is bought, the plumber quickly checks the threads, but forgets to check the sealing ring in the nut. The sealing ring may fall out during storage or transport. Always physically verify before installation that the sealing ring is present and in good condition.

5. Mechanical damage during and after installation

Damaging the flexible hose when bending

Stainless steel corrugated hoses have a minimum bending radius – this is usually stated in the technical documentation and ranges from 50 to 100 mm depending on the diameter. If the hose is bent at a sharper angle, the corrugated body "buckles" – a sharp bend forms where the metal is permanently deformed. This spot is weakened and may crack under pressure surges or vibrations.

This may not be visible at first glance – the hose may look the same, only with a slightly different shape. Therefore, it is important to handle the hose carefully during installation and never give it shapes for which it is not designed. The topic of lifespan and replacement is discussed in detail in the article Replacement of a gas flexible hose – how to recognize when it is time to replace it.

Reverse stress on connections due to appliance movement

Stoves, boilers, and other appliances move slightly during normal use. A stove is pulled out during cleaning, a boiler vibrates during combustion. If a flexible hose is installed rigidly without any movement reserve, each such movement is directly transferred to the threaded connection. Result: gradual loosening of the connection or material fatigue in the braid.

Correct solution: the hose must always have a slight excess length (but not hanging loops) and must be installed so that the appliance movement within normal operation does not mean pulling the hose. A stove should have height adjustment on its feet and, after adjustment, should stand stably without the need to adjust the hose.

6. Errors during leak testing

Using an open flame to detect leaks

This "method" is so dangerous that it is almost unbelievable that it is still practiced. Never, under any circumstances, use a lighter, match, or any open flame to test gas tightness. In addition to the extreme risk of explosion and burns, even a small spark can cause permanent damage to the installation.

Correct methods: a foaming solution (soap water – thoroughly foamed with a sponge and applied to the connection), or an electronic gas detector. Soap water will form bubbles at a leak. An electronic detector is more accurate and can detect micro-leaks that do not show up as bubbles. The entire leak testing procedure is described in the article Tightness of gas connections – how to check for gas leaks yourself.

Early disconnection of test pressure

During pressure testing (usually 150 mbar for distribution equipment or according to the project documentation), it is important to maintain pressure for a sufficiently long time – at least 15 minutes, up to 30 minutes for larger installations. A common mistake: the plumber sees that the pressure holds for the first 2 minutes and releases the connection. Micro-leaks may only become apparent after a longer time, when the sealing material or PTFE tape is fully compressed.

7. Legislative and inspection errors

Work without authorization

According to Slovak law No. 124/2006 Coll. on safety and health protection at work and the SÚBP decree, work on gas installations is defined as a specific activity requiring a qualified person with the appropriate authorization. This does not apply, for example, to replacing an appliance of the same type (under exactly the same conditions and using the original connection points), but any change in the layout, adding a shut-off valve to a fixed installation, or changing the location of the connection point requires a qualified professional.

In practice, this means: replacing a flexible hose or a ball valve in the original location can be done by a technically skilled owner, but without inspection and a professional record, it may be an issue in the case of an insurance event. Always find out what in your specific case requires inspection and what does not – the inspection technician will explain this to you before the work, not after.

Installation without documentation

Every new component should be documented – at least with a photo before covering, ideally also with the batch number and installation date. For gas hoses, there is a legislative requirement: flexible gas hoses must be regularly replaced according to the manufacturer's stated lifespan (usually 10 years from production, not from installation). Without documentation of the production and installation dates, it is difficult to prove that the hose is still within warranty.

8. Combining components from different manufacturers and classes

Another, less obvious error, is combining components that have the same nominal values but different tolerances. For example: a ball valve from one manufacturer has a slightly different thread diameter (within tolerance), and a flexible hose from another manufacturer has a thread in a different part of the tolerance. Both are "correct" according to the standard, but when combined, the thread is slightly looser. This in itself does not mean a leak, but the sealing works under worse conditions.

Therefore, it is a professional practice to use complete systems from one manufacturer or at least verified combinations. If you combine components from different brands, always test the tightness more thoroughly and be especially careful when selecting sealing materials.

We also address the topic of selecting suitable combinations in the article Ball valve vs. other types of gas shut-off valves – when to use which, where you will find an overview of different types of shut-off valves and their suitability for specific applications.

9. Errors in storage and handling of components

Pipeline components are more sensitive to storage than is commonly assumed. Specifically:

• UV radiation: rubber seals in the nuts, as well as rubber hoses (if used), degrade when exposed to direct sunlight for a long time. Store components in boxes or in a dark storeroom.
• Temperature extremes: flexible hoses must not be stored at temperatures below -20 °C or above +60 °C. Permanent deformation of the corrugation may occur.
• Mechanical pressure: do not place heavy objects on packages with flexible hoses. Deformation of the corrugation during storage is not visible, but weakens the hose.
• Open threads: plastic thread caps that are part of the original packaging are there for a reason. Without the caps, the threads get dusty and may corrode (less with brass valves, but faster with some steel parts).

Similarly, when replacing an old appliance – if you find an old welded or corroded valve on a rigid pipe, always replace it with a new, certified component. An old valve may look solid, but its seal is in poor condition after years and may crack during turning (opening/closing).

Frequently asked questions (FAQ)

Can I install a ball valve for gas myself, without an installer?

It depends on where in the installation you are installing it. Replacing a valve at its original location (for example, replacing an old valve with a new ball valve) at a closed main shut-off valve can be done by a technically capable person. However, any change in the layout, adding a new outlet, or changing the position of a shut-off valve requires a qualified professional and inspection. If in doubt, always consult with an inspection technician in advance – it is cheaper than dealing with problems after the intervention.

How long does a gas flexible hose last and when should it be replaced?

Most manufacturers specify the lifespan of stainless steel corrugated flexible hoses as 10 years from the date of manufacture (not from installation). In addition to this period, you should replace the hose immediately if you notice mechanical damage to the braiding, corrosion, kinks, or any suspicion of gas leakage. Never wait until the end of the warranty period if the hose shows signs of damage. More in the article Replacement of a gas flexible hose – how to recognize when it is time to replace it.

What to use to seal gas pipe threads – tape or paste?

Both approaches are correct, provided the product is certified for gas. PTFE tape (Teflon) is suitable for most threaded connections and is easily available. Sealing compound (e.g., Fermit Gas, Unipak Gas) is more suitable for larger diameters and places with vibrations, where tape may be less reliable. Hemp (flax) is absolutely unsuitable for gas and must not be used.

How can I tell if I have a gas leak without special equipment?

The simplest method is soapy water – a thick foam solution applied to each connection. Bubbles will form in the case of a gas leak. Apply the solution with a brush or sponge and observe for at least one minute. For more reliable results, it is good to perform the check at full working pressure after opening the main shut-off valve. Never use an open flame. For regular inspection of the entire installation, we recommend investing in an electronic gas detector – for 30–60 € you will get a reliable device for years. A detailed procedure can be found in the article Tightness of gas connections – how to check for gas leaks yourself.

Is it possible to use a longer flexible hose than needed and make a loop?

No, this is an inappropriate practice and is in conflict with the installation instructions of most manufacturers. A hose in a loop can be mechanically damaged, and when bent at a sharp angle, the corrugation can be damaged. In addition, loops are difficult to see during visual inspections and can collect condensation. Always choose a hose of the correct length – or if the distance is large, use a longer model, for example Flexira xConnect Gas Standard R1/2(T)-G1/2, 2000 mm.

Can I use any ball valve for gas if it has the right thread?

Definitely not. The ball valve must be explicitly intended and certified for gaseous media (marked "Gas", certificate EN 331). Water installation valves are designed for different seals and different operating conditions. Even if the thread fits perfectly, the seals in the ball seat are not resistant to hydrocarbons and degrade over time. For larger gas pipe diameters, a suitable choice is for example ball valve for gas FF 2" internal/internal thread, with lever, which is directly certified for this use.

Conclusion – prevention is cheaper than repair

Installation of gas installation components is not rocket science, but it requires careful attention to detail and strict adherence to rules. Most of the errors I see in practice are not the result of ignorance of basic principles – they are the result of haste, saving in the wrong place, or simply lack of attention at moments when someone assumes that "it will definitely be fine".

A gas installation is an area where it pays to be slow and thorough. The right component, the right seal, the right installation, and a thorough tightness check – these are the four pillars of a safe and long-lasting gas installation. Every minute saved during the check can potentially be very costly in the case of a gas leak or worse scenario.

If you are unsure about component selection, take a look at other articles in this Knowledge Center – for example Connecting an appliance via a gas flexible hose – step by step for a detailed practical procedure, or Common questions about gas installation components – valves, hoses, fittings for answers to specific situations from practice.

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