How to Install a Stern Water Valve Step by Step – DIY or with a Plumber

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Installation of Stern faucet – step by step – DIY or with a plumber

Replacing a faucet is one of those home repairs where an experienced handyman can easily manage without the help of a professional – as long as they know what they're doing, have the right tools, and proceed patiently. On the other hand, the same job in the wrong hands can end up with a flooded bathroom, damaged underfloor piping system, or a void warranty on the new faucet. This article will take you through the entire process from the first turn of the water shut-off valve to the final test run – and at the same time it will show you where it makes sense to call a professional.

If you're still undecided about which faucet to actually buy, we recommend reading the article How to choose Stern faucets – what to focus on before buying, where you'll find an overview of types, parameters, and selection criteria. Likewise useful is the article What diameter and connection spacing do you need for a bathroom faucet – without the correct dimensions, you won't be able to install even the most beautiful faucet to your existing plumbing.

Why Stern faucet installation is specific – and not always trivial

Stern faucets cover a fairly wide range of types: single-lever basin faucets, double-spout, shower, bathtub, wall-mounted, and pedestal. Each type has a slightly different installation procedure, different requirements for pipe preparation, and different requirements for connection tightness. What applies to a standard pedestal basin faucet with a G 3/8" connection does not automatically apply to an underfloor bathtub faucet with a thermostat.

Stern faucets are manufactured according to European standards (EN 200, EN 816 and others), which means standardized dimensions of connecting threads, standardized spacing distances, and a standardized range of operating pressures – usually 0.05 to 0.8 MPa (i.e. 0.5 to 8 bar). That's good news: you don't have to deal with exotic adapters and most spare parts are easily available. More about certificates and standards can be found in the article Certificates and quality of Stern faucets – what standards and warranties mean for you.

What you will need – tools and materials

Before you start removing the old faucet, prepare everything you need. Nothing is more unpleasant than having the water cut off for the entire floor and then realizing you're missing the key of the right size.

Basic tools

Adjustable (French) wrench – ideally two of different sizes (up to 32 mm and up to 50 mm)
Mounting wrench for faucets (long square wrench for access under the sink) – sold as a "sink wrench" or "faucet wrench"
Screwdriver – flat and cross-head, possibly bitmagnets for a drill
Hex key set – most modern Stern faucets use hex keys for fixing bracket screws
Hose wrench – for unscrewing old metal connecting hoses
Bucket or tray and cloths – there will always be residual water in the pipes
Headlamp or flashlight – it's hard to see under the sink or in the cabinet
Silicone (sanitary) – for sealing the base of the faucet against the surface of the sink/basin, if required by the manufacturer

Sealing materials

Teflon tape (PTFE) – for external threads of connections
Hemp fiber + paste (e.g. Fermit) – for stronger connections on older systems
Rubber seals (O-rings) – usually included with the faucet, but have spares
New connecting hoses (flexible) – when replacing a faucet, it is almost always reasonable to replace them as well; buy them with a length of 30–50 cm and with G 3/8" on the faucet side and G 1/2" on the side of the angle valve

Step 1 – Shutting off the water and draining the pipes

This is the step where people most often make the first mistake: they close only the angle valve under the sink, don't check if it actually holds, and then wonder why water is spraying out when they unscrew the hose. An angle valve that hasn't been closed for years has a strong tendency to leak on the first turn.

The correct procedure:

Close the hot and cold water angle valves (usually under the sink or behind the bathtub).
Open the faucet fully – this will drain the residual water from the hoses and at the same time confirm that the valves actually seal. If water continues to flow without reducing the flow, the angle valve is leaking – you must shut off the water at the riser or apartment shut-off valve.
Let the water drain completely. Place a bucket or deep tray under the connection.
For bathtub and shower faucets with underfloor installation, you must always shut off the water at the riser – angle valves are usually not accessible there.

From practice: Older housing stock from the 80s and 90s often has corroded or never-replaced shut-off valves. If you're not sure about the condition of the angle valves, it's better to call a plumber before the actual faucet replacement – the risk of a flooded bathroom is real.

Step 2 – Removing the old faucet

Pedestal basin faucet

Most basin faucets are held in place by one or two nuts fastened from below through the hole in the sink. Access to them is tight and without a long mounting wrench it's almost impossible. Procedure:

Unscrew the connecting hoses (flexible) from the faucet and from the angle valves – start from the faucet side, where there is less pressure.
Unscrew the nut(s) holding the body of the faucet from below. Be careful – if the faucet is old, the nut may be corroded; use WD-40 or a similar penetrant and wait 10–15 minutes.
Pull the faucet up.
Clean the area around the hole in the sink – old sealing gasket or silicone must be removed; a scraper and isopropyl alcohol are your friends.

Wall-mounted shower or bathtub faucet

This process is more complex because the faucet is directly screwed into the wall outlets with water supply:

Unscrew the decorative caps (rosettes) – these are usually unscrewed by hand or with an Allen key.
Under the rosettes you will find threaded outlets; unscrew the nuts or the entire body of the faucet from these outlets.
Check the condition of the fittings embedded in the wall (G 1/2" or G 3/4" outlets); if they are rusted or damaged, it is time to replace them – and this is already a job for a plumber.

Step 3 – Preparing the location and checking the pipes

Before you install the new faucet, spend a moment checking the existing pipes. This is a step that amateurs often skip – and then regret it.

Check the threads on the angle valves or wall outlets. A damaged thread will leak or "twist" when tightening new hoses. If you see a worn thread, don't tighten it "by force" – rather call a plumber.
Check the water pressure – open the angle valve and let it run for a while. If you have a pressure in the apartment building higher than 0.5 MPa (5 bar), the faucet can handle it, but the connecting hoses must be dimensioned for it. The peak pressure when opening in all apartments in the morning can reach up to 6–7 bar.
Spacing of the connections – for sink wall-mounted faucets, the standard spacing of hot and cold water outlets is 150 mm (for wall-mounted faucets). For single-hole wall-mounted faucets, the spacing is not relevant – both supplies lead into one hole. More in the article What diameter and spacing of connections do you need for a bathroom faucet.
Clean the surface at the base of the new faucet from old silicone and limescale. A clean surface is the basis of a tight and aesthetic connection.

Step 4 – Installation of the new Stern faucet

Wall-mounted faucet with one hole (monoblock)

Modern single-lever sink faucets from Stern are mostly monoblock construction – the body of the faucet passes through one hole in the sink (standard hole diameter is 35–38 mm). Installation procedure:

Put on a sealing rubber ring or silicone gasket (included with the faucet) on the faucet outlet. If not included, apply a thin strip of sanitary silicone to the lower edge of the faucet base.
Thread the connecting hoses through the hole in the sink downwards (you do this before actually lowering the faucet into the hole).
Insert the faucet into the hole – make sure the lever is correctly oriented (usually in the center).
From below, put on a plastic or metal support plate (included) and tighten the nut by hand. Then with a wrench, tighten it by another quarter to a third of a turn – do not over-tighten, the porcelain sink may crack.
If necessary, add sealing caulk between the base of the faucet and the sink surface according to the manufacturer's instructions.

Wall-mounted faucet (shower or bathtub)

Check whether the threads in the wall outlet are clean and undamaged. If necessary, blow them with compressed air or clean them with a cloth.
Wind Teflon tape around the external thread of the outlet (G 1/2") – 5 to 8 layers, winding in the direction of the thread (in the direction of tightening).
Screw in the body of the faucet (or connecting nipples, depending on the construction) by hand, then tighten with a wrench. In a masonry wall, be careful – the wall outlets are embedded in concrete and must not turn; hold them with a wrench from the other side.
Put on decorative rosettes (escutcheons) – these cover the space between the faucet body and the wall. Rosettes are usually adjusted axially to fit tightly against the wall.
Connect the shower hose or bathtub drain according to the faucet configuration.

Step 5 – Connecting the flexible hoses (flexible couplings)

Flexible hoses (flexes, flexible couplings) are the most common source of water leaks. Their correct installation is therefore crucial. On the market you can find metal flexes (braided with stainless steel), plastic braided flexes and chrome braided flexes. For bathroom taps we always recommend stainless steel braided flexes – they are more durable and long-lasting.

Never use Teflon tape on flexes with rotating nuts – these seal exclusively with rubber O-rings. Teflon tape is actually counterproductive here and can cause the O-ring to sit at an angle.
Hand-tighten the flexes and then use a wrench to tighten them another quarter turn. No more – flexes are tightened onto the O-ring, not the thread.
Check the direction of the hose: hot (red) goes to the right or to the red terminal on the tap, cold (blue/white) to the left.
Flexes must not be too tight or twisted into a sharp bend – this weakens them and they can crack over time.
Always replace old flexes with new ones – the price of new flexes is a fraction of the cost of repairs after a flood.

Standard dimensions of flexible couplings for Stern basin taps: diameter G 3/8" (tap side) × G 1/2" (valve side), length 30–50 cm. For bath and shower taps, the connections are mostly G 1/2" on both sides.

Step 6 – Test run and leak check

This is the moment of truth. Procedure:

Make sure you have towels or a bucket at hand.
Open the corner valve (or stopcock) very slowly – only a quarter turn. Let the pressure build up gradually.
Visually check all connections: corner valve – flexes, flexes – tap. Look for drops or moisture.
Open the tap fully and check the flow – it should be even without air hammer (if there is, let the tap run for a few minutes, the air will escape on its own).
Check the base of the tap on the basin – if you feel moisture here, the sealing or silicone is not holding and needs to be added.
Let the tap be under pressure for 30 minutes and then check all connections again – some leaks only become apparent after a while.

If there is any dripping: first try to tighten the connection another eighth of a turn. If that doesn't help, unscrew it, check the O-ring or thread and repeat the process. Never try to seal an active leak by force – the problem will only get worse.

Special cases – under-tile tap and thermostatic tap

Under-tile tap (under plaster)

An under-tile tap is structurally divided into two parts: the body (housing) installed in the wall during the rough construction or renovation, and the external control panel (lever, thermostat) mounted only after tiling. Installing the body into the wall is a job for a plumber during renovation – it requires proper placement, embedding, observing the depth of installation (usually 5.5–7 cm from the plane of the future tiling) and a water-tight test before tiling. You can then install the external panel yourself according to the instructions.

Thermostatic tap

Stern thermostatic taps have a built-in thermostat that maintains the set water temperature. Installation is identical to a standard wall-mounted tap, but there is one specification: the thermostat requires that the pressure difference between hot and cold water does not exceed a certain value (usually no more than 2:1). If the pressure of hot and cold water is significantly different (e.g. a heater with low pressure), the thermostat will not function properly. In such cases, a balancing valve is necessary.

When to call a plumber – clear signals

There are situations where DIY installation is inappropriate or even dangerous. From ten years of experience in customer service, we can list the most common cases where customers tried to do it themselves and ended up calling a plumber anyway – only with greater damage:

Damaged threads on wall outlets or corner valves – a layperson risks "drilling through" the thread and not stopping the leak without replacing the entire valve.
Replacing a corner valve – requires turning off the water at the stopcock and most customers are surprised that it is not a job that can be done "in five minutes".
Under-tile installation from scratch – drilling, placing the body, pressure test, embedding into the wall – this is a complex job.
Unusual water pressure (under 1 bar or over 6 bars) – requires special solutions (pump or pressure reducing valve), not just replacing the tap.
Moisture in the wall or behind the tiling – if you discover moisture when removing old taps, stop the work and call a professional. The problem is deeper than just the tap.
Water heater or storage heater in combination with a tap – setting up pressure reducing and safety valves must be done by a professional.

Common installation mistakes and how to avoid them

From our experience with customer jobs we know a lot of mistakes that repeat themselves. Here are the most common ones:

Over-tightening nuts – porcelain basins are fragile. The tap nut is tightened only to make contact, not to be tight. If you hear or feel cracking, stop immediately.
Mixing up hot and cold water – flexes are (mostly) color-coded, but not always. Before you turn on the water, check the connection according to the markings on the tap (red = hot = right, blue = cold = left).
Missing sealing – O-rings are small and easily lost during installation. Check each connection to make sure it has a sealing.
Teflon on rotating nuts – as we have mentioned, Teflon tape belongs only on external threads (nipples, fixed outlets), not on rotating nuts of flexible hoses.
Not following the winding direction of Teflon – the tape is wound in the tightening direction (when viewed from above, clockwise for a right-hand thread). Teflon tape wound the opposite way unwinds when tightened and does not press.
Installation without turning off the water – sounds absurd, but it happens. The customer does not close the valve, thinking they will just "tighten it" – and ends up with a flooded room.
Not checking the length of the flex – flexes are too short and under tension, or too long and bent into a sharp curve. Both are sources of problems.

Maintenance after installation – what to do next

The new Stern tap is working properly, sealing and flowing evenly. What next? Regular maintenance will extend the life of the tap to 10–15 years or more. More details can be found in the article Cleaning and descaling a bathroom tap – how to extend its lifespan. Here are the key points:

Once every 6 months, clean the aerator (mesh at the outlet) – unscrew it manually, rinse it, and remove limescale with vinegar.
Once a year, check whether the tap is dripping or leaking when idle – even a small drip may indicate a worn cartridge. More in the article Dripping or leaking Stern tap – causes and repair.
If you have very hard water (hardness over 30 °dH), consider installing a filter or water softener – it protects not only taps but the entire plumbing system.
Do not unnecessarily move the lever head to extreme positions – a cartridge lasts longer with gentle operation.
If you are not going to use the tap for a longer period (e.g., a cottage), close the angle valves and open the tap – drain water from the body of the tap to prevent cracking in the cold.

Comparison of installation of different types of Stern taps – summary table

Tap type	Connection diameter	Installation difficulty	Special tool	Recommendation
Bathroom pedestal tap	G 3/8" / G 1/2"	Low	Tap wrench	DIY
Wall-mounted shower tap	G 1/2"	Medium	Double wrench	DIY (if the connections are in order)
Wall-mounted bath tap	G 1/2" / G 3/4"	Medium	Double wrench, hose	DIY
Undermount tap	G 1/2"	High	Milling, mason's tools	Plumber
Thermostatic tap	G 1/2"	Medium–high	Pressure gauge	Professional pressure assessment
Kitchen tap for sink	G 3/8" / G 1/2"	Low–medium	Tap wrench, hose	DIY

Frequently asked questions (FAQ)

Do I need to turn off the water supply to the entire riser when replacing a bathroom tap?

No, if you have functional angle valves under the sink. It is enough to close the hot and cold water angle valves, confirm that they are actually sealing (open the tap and check whether the water stops flowing), and then proceed with the installation. You only need to reach the riser if the angle valves are not sealing or need to be replaced.

Why is my new Stern tap dripping at the base after installation – where is the problem?

Dripping at the base of the tap (where it sits on the sink) is almost always a sealing issue between the body of the tap and the sink surface. Solution: unscrew the tap, clean the surface dry, apply a new rubber gasket (if included) or a thin strip of silicone sealant, and reattach the tap. Let the silicone dry for 24 hours before using water for the first time.

What is the correct water supply spacing for wall-mounted Stern taps?

The standard spacing for hot and cold water connections for wall-mounted shower and bath taps is 150 mm (center to center). This is the European standard, followed by almost all manufacturers including Stern. If you have an older apartment with different spacing (e.g., 120 mm or 200 mm), you will need adapters or pipe adjustments. More in the article What diameter and connection spacing you need for a bathroom tap.

Can I use old flexible hoses (flexy) when installing a new tap?

Technically yes, practically no. Old flexy hoses may have cracked braiding, worn O-rings, or rusted nuts. The risk of water leakage is much higher than the cost of new flexy hoses (typically 2–5 euros each). Replace the flexy hoses with every tap change – it is the most common and cheap insurance against a flooded bathroom.

How many layers of Teflon tape should I apply to the thread?

For most G 1/2" and G 3/8" threads, 5 to 8 layers of Teflon tape wound in the direction of the thread are sufficient. The tape must be stretched and evenly distributed along the entire threaded part, without gaps. Too few layers – it won't seal; too many (over 12–15 layers) – the thread is hard to tighten and damage may occur. With hemp thread and paste, the process is slightly different – the hemp is worked into the thread grooves and the paste is applied from the outside; this combination is firmer and suitable for solid joints where you don't want to unscrew the tap in the future.

What if the new tap makes a knocking sound or emits noise after installation – is that normal?

Noises or knocking (so-called water hammer, hydraulic shock) when closing the tap are not normal and are related to excessively high water pressure in the pipes or the absence of a hydraulic damper (expansion tank). Modern single-lever taps with ceramic cartridges close very quickly, which at high pressure causes pressure shock waves. The solution is to install a pressure-reducing valve after the main shut-off valve (ideal operating pressure is 2–4 bar) or install a pressure expansion tank. We recommend solving this with a plumber.

Conclusion – a successful installation is the result of preparation, not strength

Installing a Stern water tap is not rocket science – but it is not a job that can be done in five minutes without preparation either. If you allocate enough time (plan for 1–2 hours for your first replacement), prepare the right tools, replace the flexy hoses and sealing materials, and follow the steps described above, you can handle most common tap types yourself. You will save on plumber costs and gain the feeling that you know what you have in your wall.

If you are unsure about the technical condition of the plumbing, it is an undermount installation, or you have any doubts about the sealing of existing valves – call a professional. A plumber working for two hours is much cheaper than the damage caused by a flooded bathroom or long-term wall dampness.

View the full range of Stern water taps at atria.sk – you will find bathroom, shower, and bath taps of various types here, and we are happy to advise you on selection and installation details. And if you are deciding before purchase, don't forget the companion article Single-lever vs. two-handle taps – which one suits your bathroom, where we compare both types from a practical perspective of everyday use.

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.