Common Issues with Water Filters and How to Fix Them
Common problems with water filters and how to solve them
A water filter is a device that most people buy, install – and then forget about. At least until something starts to go wrong. The water begins to smell, the pressure at the tap drops to half, the filter leaks or the softener stops regenerating salt. It is precisely at this point that most filter owners call a plumber, although many of these problems can also be solved independently – if you know what to look for.
In this article, we review the most common problems that we actually encounter during service visits and phone consultations with customers. This is a systematic overview – from the most trivial problems (neglected replacement of the insert) through moderately serious problems (leaks, blocked control valve) to situations where it is really necessary to call a specialist. For each problem, we describe the symptoms, the likely cause and the solution procedure.
1. Pressure drop after the filter
This is by far the most common problem that customers call about. The pressure decreases gradually – at first, they only notice that the shower sprays a bit less, and over time, the pressure drops to a minimum. In most cases, the cause is a clogged filter insert or filter medium.
Clogged filter insert
Filter tanks with replaceable inserts (so-called Big Blue, Slim Line and similar) have a recommended replacement interval of 3 to 6 months – but this number is based on the average quality of water from the mains. If you have a well, water with a high sediment content or higher hardness, the insert can be clogged in as little as 6 weeks. Conversely, with very clean tap water, it can last up to 9 months.
Inspection procedure: Turn off the water at the inlet valve, release the tank with a filter key (usually provided in the set), remove the insert and inspect it. A grey or brown color, visible deposits on the surface and a reduced diameter of the filter ring are clear signs that the insert is at the end of its life. Do not try to rinse it with water and return it – semi-permeable inserts, active carbon blocks or mechanical inserts with high filtration fineness (1–5 µm) cannot be effectively cleaned. Replace them.
If you have replaced the insert and the pressure has not returned, look for the problem elsewhere: it could be clogging of the supply pipe, a problem with the household water supply, or a blocked check valve.
Clogged filter medium in the pressure tank
Filters with free filter media (sand, BIRM, anthracite, Katalox Light, Pyrolox) require regular backwashing. If the automatic control valve is working properly, backwashing takes place automatically – usually once every 1–3 days. If backwashing does not take place or takes place incorrectly, the medium becomes filled with deposits, compresses and the filter layer begins to resist the flow.
The symptoms include not only a pressure drop, but also a deterioration in the quality of the filtrate – the water will start to smell again or have a discolored color. In such a case, check the settings of the control valve and perform a manual backwash. If the medium has not been rinsed for a long time (months or years), it may be irreversibly compacted – in that case, the medium must be replaced.
You will read more about this type of filter in the article Maintenance and regeneration of filter media: how long they last and when to replace them from our Knowledge Center.
Improperly dimensioned filter
Another cause of low pressure that is encountered quite often during service visits: the filter is simply too small for the household. If you have a filter with a nominal flow rate of 0.5 m³/h and your household actually consumes up to 1.5–2 m³/h (four people, dishwasher, washing machine running simultaneously), the pressure drop is physically inevitable – it is not a fault, but a poor dimensioning. The solution is to replace it with a larger filter. This issue is discussed in the article What flow rate do I need for my filter: calculating capacity according to household consumption.
2. Water leaks at the filter
Leaks at the water filter are second in frequency only to pressure drop. Most leaks can be resolved without a professional, provided you can accurately locate where the water is leaking from.
Leak between the tank and the filter head
Most common cause: damaged or dried out sealing ring (O-ring). The O-ring is located in a groove on the neck of the tank and can be easily pulled out and inspected during a media replacement. If the seal is flattened, cracked, or has signs of dried deposits, it is sufficient to replace it. It is important to use a sealing ring of the correct diameter — each filter type has a specific dimension. Replacement seals are inexpensive (usually 1–3 €) and available from the manufacturer or spare parts suppliers.
Before installation, apply a thin layer of silicone grease to the new seal — never use petroleum-based vaseline, which attacks rubber. Tighten the tank by hand and only slightly with a wrench — over-tightening the seal is just as harmful as its absence.
Leak at the threaded connection to the piping
If the filter leaks at the inlet or outlet thread, the cause is usually an incorrectly applied Teflon tape or insufficient tightening of the connection. Procedure: Turn off the water supply, depressurize the filter (button on the head or by loosening the tank), disconnect a piece of pipe, wrap the thread with fresh Teflon tape (4–6 layers in the direction of the thread), and re-tighten. With threaded connections using a union (nut), also check the internal surface of the nut and the seating of the seal.
Leak from the air vent or bypass valve
Some filters have a small air vent on the head. If it is dripping, it may be due to clogging or a faulty valve — it usually needs to be cleaned or replaced. If water is leaking from the bypass valve (bypass valve), the problem is in the sealing of the bypass section of the control valve.
3. Faults of the automatic control valve (water softeners and automatic filters)
The automatic control valve is the heart of every water softener or automatic filtration system. It controls the switching between filtration, backwash, rinse, and regeneration. Faults in the control valve are more serious and their diagnosis is more complex.
Control valve does not regenerate / does not cycle
Symptoms: the softener stops softening water (hardness after the unit rises again), salt in the brine tank remains at the same level, an iron filter again allows turbidity to pass. Possible causes include:
- Disconnected power supply: check whether the plug is inserted and whether a blown fuse has interrupted the power
- Reset program: during a power outage, most control valves lose their settings; check the time and regeneration cycle settings
- Jammed gear or motor: physically check whether the motor is rotating (during scheduled regeneration, you should hear a quiet hum)
- Clogged injector nozzle: the injector nozzle (injector nozzle) draws brine into the softener body; if it is clogged, regeneration occurs without salt and the measured hardness remains high
Cleaning the injector nozzle: The nozzle is located on the side of the control valve, usually behind a plastic cover. Unscrew it with a screwdriver, rinse it under running water, and clean it with a pin or thin wire. Never use a metallic object with a larger diameter — the nozzle is easily damaged.
An example of a solid automatic control valve for softeners is automatic softening head 1" - HYS-1, which has easily accessible service points and spare parts are readily available.
Control valve stuck in backwash or service position
This is evident when water continuously flows into the drain, or the household has no water (valve stuck in regeneration position and has not returned to filtration). The cause is usually mechanical — broken gears or a burned-out motor. Procedure: Switch the filter manually to the "service" position (sometimes possible via a button or dial on the head), connect a bypass to ensure the household has water, and call a service technician.
Softener forms salt bridges
A salt bridge is a situation where salt in the tank fuses into a solid crust, leaving an empty space underneath. It appears full at a glance, but the regeneration brine is not formed, as the contact between salt and water is interrupted. Solution: Stir the tank thoroughly with a rod or broom (carefully, only a plastic rod), break the crust, and mix the salt. Salt bridges are typical with cheap kitchen salt or in a humid storage environment.
4. Odor in water after the filter
An odor in water after the filter is a disturbing sign, as customers expect the filter to solve problems, not create them. Odors have various causes and various solutions.
Hydrogen sulfide odor (rotten eggs, sulfur)
If the water smells of hydrogen sulfide after the filter, the filter has likely created an anaerobic environment ideal for sulfate-reducing bacteria. These bacteria are harmless to health, but they produce H₂S with a characteristic rotten egg odor. The cause is usually a combination of two factors: an active carbon medium or insert that captures organic substances, and long water stagnation (the filter has been out of operation for a long time, e.g., during a vacation period).
Solution: Rinse the filter for 10–15 minutes, replace the activated carbon insert, and perform sanitation (see below). If the problem persists, consider adding UV disinfection after the filter. Read more in the article Water UV disinfection: when a filter is not enough and you need a UV lamp.
Chlorine odor after a carbon filter
This is a paradoxical situation: the customer bought a carbon filter precisely to remove chlorine, and now the water smells of chlorine. Cause: the activated carbon is saturated and has lost its adsorption capacity. The filter stops working and chlorine passes through along with other substances the filter was supposed to capture. Solution: Replace the insert or the activated carbon media. There is no way to regenerate activated carbon at home.
Plastic odor from a new filter
A new filter may have a typical plastic odor for the first 2–3 days. To eliminate it, you need to "rinse it out" – let water flow for 20–30 minutes without using it, then let a couple of liters run through a few times each day. If the odor persists for more than a week, it may be due to a low-quality plastic housing – in that case, request a replacement.
5. Problems with UV filtration
UV filters (UV disinfection) are technically simple devices, but they have specific faults that can remain undetected for a long time – because UV radiation is not visible and the device may look fine visually, but it is not working.
UV lamp does not light up or emits only a weak bluish glow
UV lamps have a limited lifespan – usually 9,000 hours of operation, which is about 12 months of continuous use. After this period, the production of germicidal UV-C radiation drops below an effective level, even though the lamp still emits visible blue light. This is a critical safety issue: the system appears to be working, but water disinfection is insufficient.
Therefore, the golden rule applies: replace the UV lamp preventively every 12 months, regardless of whether it is still lighting or not. For Viqua (formerly Trojan) systems, we recommend original spare parts, such as the Viqua S463RL UV lamp, which is compatible with several models in this series and ensures the correct intensity of UV-C radiation.
Cracked or cloudy quartz sleeve
The UV lamp is protected by a quartz glass sleeve that must remain optically clean. If scale, iron deposits, or biofilm settle on the sleeve surface, the UV radiation is weakened and disinfection is ineffective. Clean the quartz sleeve every 6 months with an acidic solution (e.g., diluted vinegar or citric acid) – never use abrasive agents that could damage the surface. A cracked sleeve must be replaced immediately, as insulation failure can cause a short circuit or water contamination.
UV system does not work on turbid water
UV disinfection has a fundamental limitation: it only works on optically clear water. If the water is cloudy (muddy, contains sediment, or has high iron content), UV rays cannot penetrate the entire volume of water, and part of the microorganisms remain unaffected. A mechanical pre-filter with a minimum of 5 µm, ideally 1 µm, must be installed before any UV system. If the water contains iron or manganese, a filter for these elements is also necessary – a suitable solution is, for example, the Water filter for iron and manganese HydroTreat BIRM 0.8 m³/h, which should be installed before the UV unit.
6. Problems with shower and inline filters
Shower filters are relatively simple devices, but we still encounter recurring problems. The most common is a pressure drop after a few months and improper installation.
Shower filters with KDF (galvanic filter with copper and zinc), such as the Shower filter with KDF 1/2", are effective in reducing chlorine, heavy metals, and partially also bacteria, but they have limited capacity – usually 10,000–15,000 liters or 6–12 months of operation. After this period, the filter media or the entire filter body must be replaced.
Practical experience: some customers install the shower filter backwards (input and output are swapped), which causes a dramatic pressure drop or no flow at all. Always check the flow direction marking (arrow on the filter body).
7. Sanitization of the filtration system
Sanitization is an underestimated aspect of filtration system maintenance. Bacteria, mold, and biofilm settle in every filter that contains organic substances or a filtration medium suitable for biological growth. Without regular sanitization, the filtration system may paradoxically worsen the microbiological quality of the water.
Procedure for sanitizing a cartridge filter with a carbon insert:
- Turn off the water supply and drain the filter
- Remove the old insert and dispose of it
- Wash the housing and head with warm water and dish soap (a one percent sodium hypochlorite solution – disinfectant, not a cleaning agent)
- Rinse thoroughly with clean water – any remaining hypochlorite could damage the new medium
- Insert the new media, mount the filter, and rinse for 5–10 minutes
For systems with BIRM or other oxidation-biological media, sanitization is done differently – by rinsing with a special disinfecting solution (usually a 5% hydrogen peroxide or hypochlorite solution) through the control valve, allowing the media to remain in contact with the solution for 2–4 hours, then rinsing with clean water to drain.
8. Problems related to the quality of the incoming water
Many problems with filtration systems are not caused by the equipment itself, but by a dramatic change in the quality of the incoming water – something customers often do not associate with the filter. Well water varies seasonally: in spring after snowmelt, turbidity is higher; in summer, nitrate levels may rise; after heavy rain, microbiology may deteriorate. Filters designed for "normal" water quality may be overloaded in these peak situations.
Practice: Customers with wells should have their water tested at least once every two years – preferably in spring (worst conditions) and in autumn. If the analysis shows a change (e.g., an increase in iron content from 0.5 to 2 mg/l), the filtration system should be reassessed. The article Iron and Manganese in Water: How to Identify the Problem and Choose the Right Filter may be helpful.
9. Biofilm formation in the piping after the filter
Customers occasionally complain that the water is white, cloudy, or has a yellowish tint – even though the filter is working properly. The cause may be the piping itself after the filter: biofilm (a thin layer of bacteria and organic matter) forms in any piping that is not disinfected. Filtration removes chlorine and other disinfectants from the water, which paradoxically facilitates the growth of biofilm in the piping.
Solution: Regular sanitization of the entire piping system after the filter (at least once a year with shock chlorination or another disinfection method) and the inclusion of UV disinfection as the final stage before consumption.
10. Hydrogen water generators – specific problems
Hydrogen water generators such as Hydrogen Water Generator HYDRO are a relatively new category, but characteristic problems also arise here. The most common issue is the deposition of scale on the PEM membrane electrodes, which reduces hydrogen production. Electrical conductivity of the water plays a key role in these devices – water that is too soft (deminerlized) does not electrolyze efficiently, while water that is too hard deposits calcium scale on the electrodes.
Regular maintenance: Once a month, rinse the chamber with a lemon solution (citric acid, 1 teaspoon per 200 ml of water) and let it sit for 20 minutes, then rinse with clean water. If the device emits ozone (a smell) instead of a hydrogen scent, the polarity of the membrane may have changed – check whether the device needs to be reset according to the instructions.
Prevention of faults: what is worth monitoring regularly
Experience from practice speaks clearly: the vast majority of water filter faults are the result of neglected maintenance, not manufacturing defects. Devices that receive regular care operate without problems for 10 or more years. Here is an overview of basic inspection points:
- Every 3–6 months: visual inspection of the filter cartridge, checking the tightness of connections, checking the salt level in the softener
- Every 6–12 months: replacement of the filter cartridge (carbon, mechanical filtration), replacement of the UV lamp, cleaning of the quartz sleeve of the UV system, checking the setting of the regeneration cycle
- Every 2–3 years: inspection of the condition of the filter media (BIRM, sand filter), water analysis, inspection of the seals of the control valve
- Every 5–8 years: replacement of the filter media, service inspection of the control valve, replacement of O-rings on all vessels
A more detailed look at the topic of media replacement can be found in the article Maintenance and Regeneration of Filter Media: How Long They Last and When to Replace Them.
When to call a professional and when you can do it yourself
Customers often ask us what they can do themselves and what should be entrusted to a service technician. Here is a summary from practice:
You can do it yourself:
- Replacement of the filter cartridge
- Replacement of the gasket (O-ring) between the vessel and the head
- Replacement of the UV lamp
- Cleaning of the quartz sleeve of the UV system
- Manual initialization of backwash or regeneration
- Breaking up the salt bridge in the softening tank
- Cleaning of the injection nozzle (if you are skilled)
- Application of Teflon and tightening of threaded connections
Call a professional:
- Replacement of the motor or gear of the control valve
- Leak from inside the control valve (faulty internal pistons or discs)
- Replacement of filter media (requires specific equipment and knowledge of the correct bed height)
- Any problem with the electrical supply of the UV system
- Unidentified turbidity or odor despite new cartridges and proper backwash
Most frequently asked questions (FAQ)
Water after the filter still smells of hydrogen sulfide even after replacing the cartridge. What am I doing wrong?
Replacing the cartridge is not enough if biofilm remains in the tank or piping after the filter. Sulfate-reducing bacteria settle on the internal walls of the filter body and the piping itself is an ideal refuge for them. The tank must be disinfected (10% sodium hypochlorite solution or 5% hydrogen peroxide, contact time 2–4 hours), then thoroughly rinsed with clean water, and a new cartridge inserted. If the problem persists, add UV disinfection after the filter.
Water softener is using salt too quickly. Is it a fault?
Not always. Salt consumption depends on the setting of the regeneration cycle (frequency and salt dose) and on the actual hardness and volume of water consumed. If you recently changed your water consumption (new household member, new appliances), the softener has adapted to a higher load. Check whether regeneration is set to "hardness-controlled" (volumetric) or only time-based – volumetric control is more efficient. A real fault occurs if salt is consumed even when no water is flowing in the household – in this case, the problem is a leak in the control valve (bypass through the valve).
Why is the pressure after the filter dropping, even though I replaced the cartridge a month ago?
With well water containing a high content of sediment, iron, or manganese, the cartridge can become clogged within 3–6 weeks. Visually inspect the cartridge – if it is brown or gray, replace it again and consider adding a coarser pre-filter (e.g., 50–100 µm mesh pre-filter basket) before the main filter to extend the life of the finer cartridge. At the same time, have a water analysis done – it may happen that the current filtration is insufficient for your water.
UV lamp is lighting up, but after water analysis, the customer found that bacteria are still present. Why?
There are three main reasons: (1) the UV lamp is old (more than 12 months) and produces insufficient UV-C output – the blue light does not mean that disinfection is effective; (2) the quartz sleeve is cloudy (scale, iron) and attenuates UV radiation; (3) the water before the UV unit has turbidity or high iron content, which shadows microorganisms from UV light. Solution: replace the UV lamp (e.g., UV lamp Viqua S463RL), clean or replace the quartz sleeve, and add a mechanical pre-filtration stage (1 µm) before the UV unit.
Iron filter (BIRM) stops working after some time. What happened?
The BIRM medium requires the presence of dissolved oxygen in the water and an optimal pH range of 6.8–9.0 for proper function. If the pH drops (acidic well water), or if there is too much manganese in proportion to iron in the water, BIRM loses its oxidizing capacity. Another cause: if backwash does not occur intensively enough (low backwash flow), the medium becomes compacted and filtration capacity is lost. Perform a manual backwash with a higher flow and let it run longer (15–20 minutes). If the problem persists, have a water analysis done including pH and CO₂.
Can I replace the filter media myself (e.g., sand filter or BIRM)?
Technically yes, practically only with good knowledge. Media replacement involves: emptying the tank, removing the old media, inspecting the distribution system inside the tank (bottom siphon and distribution basket – must not be cracked), filling the gravel layer and the filter media to the correct height (usually 60–70% of the tank volume), and setting the backwash. Errors during replacement (incorrect media height, damaged distributor) can cause media to leak into the piping. If you lack experience, we recommend entrusting the replacement to a professional. A comparison of media can be found in the article BIRM vs. Pyrolox vs. Katalox Light: Comparison of Iron Filters.
Conclusion: prevention is always cheaper than repair
Water filters are among the most reliable technologies in the household in many ways – they have no moving parts (except for the control valve of water softeners), operate passively and quietly, and with proper care can last for decades. Most of the issues described here have a common denominator: neglect of regular maintenance.
If you are unsure which type of water filtration you actually need for your household, we recommend starting with the article How to choose a water filter for your home: a complete guide. If you are dealing with a specific issue or planning a new filtration system, browse products in the Filtration category – for each product you will find technical specifications, recommended use and service intervals.
Remember: water analysis is the foundation. Without it, you are designing a filtration system blindly. With the analysis in hand, answers to most questions are straightforward – and if problems arise, they can be diagnosed quickly and accurately.
Do you have a question about this topic?
Struggling to decide or dealing with a specific situation in your home? Write to us – we are happy to help.