Replacing the Seal and Cartridge in a Tap: When and How to Do It

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Replacing the seal and cartridge in a faucet: when and how to do it

A dripping faucet in the bathroom or kitchen sink is one of those things that can slowly but surely annoy every member of the household. The rhythmic dripping at night, a wet sink in the morning, and constantly rising water bills – these are all signs I repeatedly encounter in various jobs. And yet, the solution is surprisingly simple in the vast majority of cases: replace the seal or cartridge, and the faucet will work as if it were new. This article will show you when it's time for a replacement, how to complete the entire process without calling a plumber, and what to watch out for to avoid unnecessarily complicating the job.

Why faucets start to drip – the basic physics of the problem

To understand what needs to be replaced, we first need to understand why the sealing stops working. Every water faucet operates on a simple principle: you open the valve, water flows; you close it, the flow stops. The key is sealing the moving part against the water pressure.

In older faucets (typically 20 or more years old), this is ensured by rubber seals – O-rings and flat seals made of synthetic rubber. These gradually harden, crack, or deform due to temperature, chlorine, and water hardness. The result: water finds a way around the seal and drips.

In modern single-lever faucets, this task is taken over by a ceramic cartridge – a hermetically sealed unit with two ceramic discs that precisely press against each other to regulate the flow. Ceramic is hard, chemically resistant, and under normal use can last tens of thousands of opening and closing cycles. But even a ceramic cartridge is not eternal: mechanical impurities, limescale deposits, and mechanical damage to the discs can cause the faucet to leak or become difficult to operate.

Two-handle faucets (so-called "cross" or the old type with two separate handles for hot and cold water) operate on the principle of a screw valve: by turning the handle, you screw the rubber seal onto the valve seat and thus stop the flow. In these types, the flat seal – the so-called valve seal or "cap seal" – is replaced.

How to tell what needs to be replaced

At first glance, dripping may look the same regardless of the type of problem, but in practice, there are clear signs that indicate what is the cause:

Drips from the spout (outlet) even when the faucet is fully closed – in lever faucets, it is almost always the cartridge. In two-handle faucets, it is the rubber valve seal.
Water leaks around the lever or under the handle of the faucet – the problem is not in the cartridge, but in the O-rings of the external stem. The solution is to replace the O-rings, not the cartridge.
The faucet drips only at one temperature (only cold or only hot) – in two-handle faucets, this indicates which of the two valves is damaged.
The lever moves stiffly, squeaks, or jams – the cartridge is damaged by impurities or mechanically. Replacement is usually necessary.
Flow is weaker than usual, but it seals well – it is not a matter of the cartridge or seals, but a clogged filter at the inlet or in the aerator spout.

It is also very important to know that not every drip is necessarily a problem of the seal or cartridge – sometimes the cause is back pressure in the water supply, poorly adjusted water pressure in the household (above 3 bar, faucets start to have problems, the ideal is 2–2.5 bar), or a loose connection of the supply. If you are unsure, also read our article on the topic Common problems of water faucets: dripping, weak flow, sputtering, where these scenarios are discussed in more detail.

Types of cartridges and seals – what you will find in your faucet

Ceramic cartridge

Today, this is the absolutely dominant type in single-lever faucets. It consists of a plastic or brass body, inside which are two polished ceramic discs with holes. The lower disc is fixed, the upper one moves by operating the lever. When the holes align, water flows; when they separate, the flow is interrupted. The advantage is long life (with clean water, easily 15–20 years), the disadvantage is sensitivity to hard water with high calcium content and to sand or coarse impurities that can scratch the ceramic surfaces.

Cartridges are manufactured in various diameters. The most popular are:

25 mm – standard size for most bathroom faucets
35 mm – common for medium and high-end sink and bathtub faucets
40 mm and 50 mm – larger faucets with higher flow (thermostatic heads, bathtub combinations)

Along with the diameter, the overall height of the cartridge and the shape of the inlet openings are also important – therefore, when ordering a replacement cartridge, it is always better to take the old one with you or note the manufacturer and type of the faucet.

Rubber and EPDM seals

A flat rubber disc (diameter typically 10–20 mm, thickness 2–4 mm) in older valve taps. It is screwed onto the valve seat and, when worn, becomes harder, deforms, or develops a cut. Replacement is cheap and simple, and seals are sold in sets. EPDM (ethylene-propylene rubber) is more resistant to high temperatures and chlorinated water than regular natural rubber.

O-rings

These small rubber rings seal rotating and moving parts. You will find them on the stem of the tap, on the transition of the swivel arm of the shower faucet, on the drain valve of the sink set. Common profiles: 2 mm, 2.5 mm, 3 mm. When ordering, always measure the inner diameter and profile (thickness of the ring), not the outer diameter.

Thermostatic cartridge

A special category – contains a thermostatic element (wax or bimetallic), which automatically reacts to changes in water temperature and maintains the set value. These cartridges are more expensive and their calibration is more complex. Replacement is possible, but I recommend it for expensive taps – sometimes it is more cost-effective to replace cheaper thermostatic models entirely.

When to replace and when to repair

The golden rule from practice: if the tap is older than 15 years and is leaking, consider replacing the entire tap instead of repairing it. Spare parts for old models are hard to find, and even if you manage to get a new seal, wear of the valve seat, porosity of old brass castings, or corrosion of the threads may cause the problem to return soon.

On the other hand, if you have a quality tap that is 5–10 years old and the problems are clearly localized, repair is very worthwhile. For example, replacement cartridges for ARKO series taps cost a fraction of the price of a new tap, and if you know what you are doing, the replacement takes 20–30 minutes.

Practical examples of when repair saved the customer money:

The customer had a satin sink pillar tap ARKO that was two years old – it was leaking from the spout. Cartridge replacement in 20 minutes, problem solved.
With a satin bath tap ARKO, water was leaking around the swivel arm – new O-rings on the rod were enough, for just a few cents.
The customer had an old 25-year-old cobalt tap with crossed handles – we couldn’t find a seal from any of the three suppliers, and a new tap was the only reasonable solution.

Required tools and materials

Before starting the work, prepare everything at once – you won’t want to run around the workshop or store with a partially disassembled tap.

Adjustable spanner (250–300 mm) or socket wrench 22–27 mm
Flat and crosshead screwdriver (for removing the cover and filter)
Hex key – most commonly 2.5 mm or 3 mm for loosening the lever
Plastic or Teflon tape for threads
Mild hand cleaner or non-chloride degreaser for cleaning the seat
Bowl or cloth for collecting residual water
Silicone-based lubricant (not oil-based!) for lubricating O-rings
Replacement cartridge or seals – depending on the identified fault
Camera or mobile phone – take photos of each step, including the orientation of the cartridge before removal

Be careful with one detail that I often see people ignore: never use oil-based lubricant (petroleum jelly) on rubber seals – the rubber will swell and the seal will be ruined. Only silicone-based lubricant.

Step-by-step procedure for replacing a cartridge in a single-lever tap

1. Closing the water supply

Always start by stopping the water supply. Under the sink or basin are angle valves (shut-off valves) – turn them clockwise. If your installation does not have angle valves (which is an error, but it happens), you must close the main water shut-off valve for the apartment or house. After closing, open the faucet to release pressure and allow remaining water to drain into a prepared basin.

2. Removing the lever

Most lever faucets have a screw hidden under a colored plastic cap (blue for cold, red for hot, or one for both) using an Allen key 2.5 mm or 3 mm. Carefully push the cap out with a flat screwdriver – do not force it, just gently pry around the edge. After unscrewing the screw, the lever should come off freely upwards.

3. Removing the mounting nut

Under the lever, you will see a ring nut (brass or plastic) that holds the cartridge in the body of the faucet. Unscrew it with a wrench counterclockwise. Note: some modern faucets (e.g., design series) have hidden special screws or plastic locks in this area – never use force blindly.

4. Removing the cartridge

The cartridge should come out vertically upwards with a gentle pull on the stem. If it is firmly seated, do not twist it – otherwise, you may damage the faucet body. A gentle back-and-forth turn while pulling may help. Now take a photo of how the cartridge was seated (orientation, color of sides, position of protrusions).

5. Inspecting the faucet body

Before inserting the new cartridge, look into the body opening: are there any deposits, sand, or limescale chunks? Gently clean with a wet cloth. Check the seat where the cartridge rests – if it is visibly damaged or corroded, replacing the cartridge alone will not solve the problem.

6. Inserting the new cartridge and reassembly

Before inserting the new cartridge, gently apply silicone-based lubricant around the O-rings. Insert it in the correct orientation (protrusions into corresponding grooves) and press down until it clicks into place. Tighten the nut – just enough to be secure, not forcefully. Reattach the lever, insert the screw, and cover the cap. Open the angle valve, gradually open the faucet, and check for leaks.

Procedure for replacing the washer in a two-handle faucet

Two-handle faucets have the same internal construction in each handle: handle → mounting screw or nut → threaded stem → flat rubber washer at the bottom of the stem. Procedure:

Close the water supply (angle valve for the respective circuit – cold or hot, depending on which handle is leaking).
Remove the handle: a screw or a retaining pin is usually located underneath.
Unscrew the brass stem housing with a wrench (left-hand or right-hand thread – try normally first, if it doesn't work, try the opposite direction).
Pull out the stem with the old washer. The old washer is usually a flat rubber gasket and secured by a small screw at the bottom of the stem – unscrew it, replace the washer, and reassemble.
Before reassembly, inspect the valve seat: if it has a groove or is covered with mineral deposits, clean it with a damp cloth. If it is deeply damaged, use a valve seat tool or replace the entire faucet.
Screw in the stem, reattach the handle, open the water supply, and check for leaks.

Special situation: bidet faucet with drain garniture

In bidet faucets (such as bidet faucet with drain garniture ARKO in chrome or bidet faucet with drain garniture ARKO in satin), the situation is a bit more complicated, as these faucets are connected to the drain garniture – the drain of the bidet is controlled by the faucet mechanism via a rod or cable.

If it is leaking from the spout, the procedure is the same as with a standard lever faucet – replace the cartridge. However, if it is leaking around the drain mechanism rod or running down the body of the faucet to the bidet, the problem is the seals of the drain mechanism, not the cartridge. These seals (O-rings and flat washers) are part of the drain garniture and can usually be replaced separately.

More about what is included in the package and what needs to be purchased separately can be found in the article Bidet faucet with drain garniture: what is included in the package and what needs to be purchased separately.

Most common mistakes during replacement – what to avoid

Over the years of working on customer sites, I have seen just about everything. Here are the mistakes people repeatedly make:

Forgetting to close the water supply. Sounds silly, but it happens – especially when the angle valve is stuck and seems not to work. Always check the closure by opening the faucet before disassembly.
Purchasing a cartridge without checking the dimensions. They buy based on appearance or model name, but cartridges are not universal. Always measure the diameter and height of the old cartridge.
Inserting the new cartridge upside down. A ceramic cartridge has a fixed direction – if you don't follow it, hot water will go to the cold side and vice versa, or the faucet will immediately drip.
Tightening the cartridge nut too much. Ceramic is hard, but the body of the faucet (especially plastic-brass composites) can break. Tighten with your hand + a gentle turn with a wrench, not by force.
Not lubricating the O-rings. A dry O-ring can easily twist or tear during installation. Always use silicone.
Ignoring the valve seat. A new washer on a damaged seat will start dripping again in a week.
Forgetting to check the filter/screen during inspection. If the flow remains weak after replacing the cartridge, always check the aerator screen and inlet – it is usually clogged with limescale.

Replacement cartridges and seals – where to find them and what to watch out for

When looking for replacement parts, a few rules apply:

The best choice is an original part from the manufacturer of the faucet. If you know the manufacturer and model (sometimes it is engraved on the body or in the warranty card), contact an authorized dealer. An original cartridge is guaranteed to fit and has the same parameters.

The second option are compatible cartridges according to dimensions. If you know the exact diameter of the cartridge (e.g. 35 mm) and its height (e.g. 64 mm), you can find generic cartridges from reputable manufacturers such as Kerox, Sedal or Lidah. These companies produce OEM cartridges for dozens of faucet brands and the quality is comparable to originals.

Avoid cheap unknown cartridges from markets and dubious e-shops. The ceramic must be precisely manufactured – even a small deviation in the flatness of the discs will cause the cartridge to leak immediately after installation. Cheap cartridges also have a shorter lifespan of the discs.

For seals and O-rings, it is true that they are largely standardized (ISO 3601). Always measure: inner diameter (ID) and profile thickness (CS). For example, a standard O-ring 10×2 means ID 10 mm, thickness 2 mm. Sets of O-rings in various sizes can be purchased in any hardware store.

What are the costs of repair vs. replacement

Practically speaking, the costs for an average bathroom faucet are as follows:

Set of O-rings – 1 to 5 € (standard sizes)
Rubber valve seal – 0.50 to 2 € per piece
Generic ceramic cartridge (25 mm) – 4 to 12 €
Original ceramic cartridge (35 mm, premium faucet) – 15 to 35 €
Plumber – cartridge replacement (labor) – 30 to 80 € including delivery
New mid-range faucet – from 40 to 150 € (depends on the series and finish)

The conclusion is clear: if you can do it yourself, repairing the cartridge is much cheaper than replacing the faucet. If not, for a cheaper faucet (up to 50 €), it is not financially worth it to have it repaired by a plumber and it is more reasonable to replace the faucet. For a higher quality faucet, the repair is always worth it.

Specifics for different types of faucets in the bathroom

Basin faucets

Faucets such as 946487 basin mounted faucet LOOP are among the most sold and also the most frequently repaired types, because the kitchen sink is used intensively. Cartridges for basin mounted faucets are mostly 35 mm with a higher flow rate. Also check the filter at the inlet of the hose – more sediments get into the water in the kitchen.

Bathtub faucets

Bathtub faucets are less stressed by the number of cycles, but are exposed to higher temperatures. Seals here last longer, but at the first signs of dripping, it is good to act in time, because bathtub faucets are often less accessible (mounted on the wall or on the tub). Tip: if you have a bathtub faucet with a handheld shower, also check the seal at the hose coupling – this is a place where the seal wears out faster.

Wall-mounted faucets

This situation is more complicated. The body of the faucet is built into the wall and access to the cartridge is only through a cover. Replacing the cartridge is technically the same, but the space is more limited. More about this type can be found in the article Wall-mounted vs. Basin-mounted Faucet: Which One is Suitable for Your Bathroom.

Prevention: how to extend the life of seals and cartridges

From years of experience, I know that many problems can be avoided by simple measures:

Install a water softener or filter if the hardness is over 20 °dH (German degrees). Hard water is the number one enemy of ceramic cartridges.
Correct water pressure – ideally 2 to 3 bar. Over 4 bar consider a pressure reducing valve. High pressure accelerates the wear of seals.
Do not force the faucet – if the tap turns difficult, it is not a reason to add force, but a signal that it is time to replace or clean the cartridge.
Regular descaling of the aerator – a clogged aerator increases back pressure and thus loads the seals. A simple vinegar once every six months is enough.
Avoid chemical cleaning agents on the surface of the faucet – chlorine-based cleaning agents can penetrate the seals and accelerate their degradation. More about proper cleaning can be found in the article How to Maintain and Clean Faucets Without Damaging the Surface.

Common questions (FAQ)

How do I find out what diameter of cartridge I need?

The most reliable way is to disassemble the cartridge and measure it with a caliper or ruler – the diameter at the widest point of the ceramic body (not the plastic ring). Common sizes are 25, 35 or 40 mm. If there is a manufacturer's brand and number on the cartridge, you can look for the exact equivalent online. Never rely solely on visual comparison – even a millimeter difference can mean that the cartridge does not fit.

Can I clean the cartridge instead of replacing it?

Yes, sometimes yes. If the faucet is still relatively new and the problem is hard operation or slight dripping from minimal dirt, you can try to remove the cartridge, rinse it under running water, gently remove deposits with a soft cloth and soak it for an hour in a solution of water + white vinegar (1:1). Ceramic surfaces must not be scratched or sanded. If after cleaning it still leaks or is difficult to operate, replacement is necessary.

The faucet still drips after replacing the cartridge – what to do?

The most common cause is incorrect orientation of the new cartridge – remove it and check whether the protrusions fit into the grooves and the colors of the sides (blue/red) correspond to the sides of the supply. The second possibility is a damaged seat of the faucet body on which the cartridge rests – if there is a scratch or corrosion there, the new cartridge will not seal. The third possibility is the O-ring on the outside of the cartridge, which twisted or torn during installation – remove the cartridge, check the O-ring, grease with silicone and insert again.

Is it better to replace the cartridge or the entire faucet?

It depends on the age and quality of the faucet. A faucet under 10 years old in good condition: replace the cartridge. A faucet older than 15 years with multiple symptoms (hard operation, old design, hard to find replacement parts, corrosion on the surface): it is worth investing in a new faucet. Modern faucets have much better surface resistance and longer cartridge life than models from 20 years ago.

Water is dripping around the faucet (not from the spout) – what should I replace?

If water is dripping around the outside of the faucet – around the spout, when the lever is applied or under the base of the faucet – it is not the cartridge, but the external sealing O-rings. These are located on the spout of the cartridge or in the body of the faucet above the cartridge. Sometimes it is enough to remove the cartridge, replace only these external O-rings (cost a few cents) and the problem is solved. Water dripping under the base of the faucet (between the faucet and the sink) usually does not relate to the cartridge – check the base sealing or the supply lines.

How long does a new cartridge last?

A quality ceramic cartridge from a reputable manufacturer (Kerox, Sedal, Lidah, Grohe, Hansgrohe OEM) has a lifespan of 150,000 to 500,000 opening/closing cycles, which at normal use corresponds to 15 to 30 years. In practice, this is shortened by hard water, high pressure and impurities in the water supply system. With soft water and correct pressure, a 20-year lifespan of a ceramic cartridge is commonly achieved.

Conclusion: repairing a faucet is a good investment if you know what you are doing

Replacing a seal or cartridge belongs to those repairs where it is worth learning to do it yourself. It is not rocket science – just a bit of patience, correct identification of the problem, a suitable replacement cartridge and following the procedure. This way you save not only money on the plumber, but also time waiting for an appointment and you have the certainty that you know what was done and with which parts.

If you have decided that your faucet is too worn and repair is not meaningful, take a look at our faucets – you will find there models for every type of installation, various surface finishes (chrome, satin, black matte) and various price categories. Choosing a new model will also help you with our article How to choose faucets for the bathroom and kitchen.

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