Reverse Osmosis Troubleshooting: How to Diagnose and Fix Common RO System Problems

Most reverse osmosis system problems trace back to four root causes: fouling, scaling, mechanical failure, or chemical attack.

Fouling and scaling build up gradually on the membrane surface. Mechanical failure hits suddenly, usually as a pump, valve, or seal gives out. Chemical attack degrades the membrane material itself, often from chlorine exposure.

AXEON Supply has engineered and manufactured membrane filtration systems and components for 37 years. Our in-house technical support team runs these exact diagnostics daily for customers across the United States and Canada.

This guide walks through each fault category using the same pressure, flow, and water quality checks our support team uses on a live troubleshooting call. Start with feed pressure and TDS rejection. These two checks eliminate most causes fastest.

What Causes Most Reverse Osmosis System Problems?

Most reverse osmosis system problems fall into four categories: fouling, scaling, mechanical failure, and chemical attack. Fouling and scaling reduce membrane performance gradually. Mechanical failure disrupts pressure and flow immediately. Chemical attack degrades membrane material permanently.

Fouling happens when suspended solids, colloids, and biological growth accumulate on the membrane surface. This buildup blocks the membrane's pores and reduces permeate flow. Sediment filters installed ahead of the membrane remove these particles before they reach it.

Scaling happens when dissolved minerals in the feed water exceed their solubility limit and crystallize on the surface. Common scale-forming minerals include calcium carbonate, calcium sulfate, and silica. Scaling and fouling shortens service life and lowers rejection rate over time.

Water softeners remove hardness minerals before they reach the element, cutting scaling risk significantly. Chemical dosing systems inject antiscalant compounds that keep dissolved minerals suspended in solution instead of crystallizing on the surface.

Mechanical attack covers pump failure, valve failure, and physical damage to housings or fittings. A failed booster pump cannot maintain the pressure a membrane needs to produce water. A stuck flow control valve disrupts the balance between permeate and reject flow.

Regular inspection of pumps, valves, and housings catches mechanical wear before it causes a full system failure. Replacement parts kept on hand shorten downtime when a component does fail.

Chemical attack happens when chlorine or an incompatible cleaning chemical oxidizes the membrane polymer. Chlorine breakthrough occurs when a chlorination system or upstream carbon pre-filter fails to remove chlorine before feed water reaches it. This damage is permanent and requires replacement, not repair.

Monitoring feed water chemistry and confirming pre-treatment equipment works correctly protects the membrane from this kind of damage. AXEON Supply's technical support team can help interpret a water quality analysis to confirm which category is driving a specific system's symptoms.

Why Is My Reverse Osmosis System Producing Little or No Water?

Low or no water production from a reverse osmosis system usually traces to one of four causes: clogged pre-filters, low feed pressure, a fouled or scaled membrane, or a failed storage tank bladder. Checking pressure first narrows the diagnosis fastest.

Check feed pressure first. Most residential and light commercial reverse osmosis systems require a minimum of 40 PSI to operate correctly. The optimal range for consistent membrane performance runs from 60 to 80 PSI. Feed pressure below 40 PSI drops permeate output sharply, regardless of how well the membrane is functioning.

A pressure gauge installed at the system inlet confirms actual feed pressure in seconds. Low pressure readings point to a municipal supply issue, a partially closed feed valve, or a failing well pump upstream of the system.

Inspect sediment and carbon pre-filters. These filters remove particles and chlorine before water reaches the membrane. A clogged pre-filter restricts flow before the membrane ever sees the water, starving the system of the pressure it needs.

Replace pre-filters every 6 to 12 months, depending on source water quality. Source water carrying heavy sediment or high chlorine levels calls for more frequent replacement than clean municipal supply.

Test the RO membrane's TDS rejection rate. A healthy membrane rejects 95 to 99 percent of total dissolved solids from the feed water. Rejection below 90 percent signals fouling, scaling, or aging that requires replacement.

Most RO membranes last 2 to 3 years under normal operating conditions. A membrane operating past this range, combined with a falling rejection rate, is the most likely cause of declining output.

Check the storage tank precharge. A properly precharged tank reads 7 to 8 PSI of air pressure when empty. Test this with a tire pressure gauge at the tank's air valve.

A tank reading significantly below this range, or one that spurts water when tested, has a ruptured bladder. A ruptured bladder cannot hold pressure and requires tank replacement, not repair.

Inspect the flow restrictor. It meters water to the drain to maintain the pressure differential that drives water through the membrane. A clogged or mismatched restrictor reduces permeate output even when pressure and the membrane are both functioning correctly.

Confirm the flow restrictor's rating matches the membrane's output specification. A restrictor sized for a different membrane disrupts this balance.

AXEON Supply account holders with an unresolved output issue after these checks can contact our technical support team. Have the system model and serial number, a current water quality analysis, and a description of the steps already taken ready before calling.

Why Does My Reverse Osmosis System Keep Running or Never Shut Off?

A reverse osmosis system that runs continuously or never shuts off typically points to a failed automatic shut-off valve, insufficient storage tank pressure, or a bleeding check valve. Isolating which component is failing takes three simple pressure tests.

Test the automatic shut-off valve. This valve, often called the ASO valve, closes when tank pressure reaches roughly two-thirds of incoming line pressure. Its job is to stop water flow to the drain once the tank reaches capacity.

Close the tank valve and watch the drain line. If drain flow stops, the ASO valve is functioning correctly and the tank itself is the likely cause. If drain flow continues, the ASO valve requires replacement.

Check for a bleeding check valve. It sits at the permeate outlet and prevents backflow into the membrane. A check valve that bleeds pressure keeps the system from ever reaching shut-off pressure.

Fill the tank completely with the tank valve open, then shut off the incoming water supply. Continued flow to the drain after the supply is off confirms the check valve is bleeding pressure.

Verify storage tank precharge. A tank running low on air pressure never builds enough resistance to trigger the ASO valve. Confirm the tank reads 7 to 8 PSI when empty, using the same test described for low output.

Inspect for a missing or failed flow restrictor. A missing restrictor sends far more water to the drain than the system was designed for, and this shows up as continuous, unusually loud drain flow alongside the shut-off problem.

Commercial and industrial systems feel this problem harder than residential units. A continuous-run fault on a higher-volume system wastes more water per hour and puts sustained strain on the booster pump, so diagnosing it quickly matters more on a commercial installation than on a single residential unit.

What Causes Leaks in a Reverse Osmosis System?

Reverse osmosis system leaks most often occur at fittings, membrane housing O-rings, and storage tank connections. Most leaks trace to a worn or improperly seated O-ring rather than a cracked housing or major component failure.

Leaks show up in a predictable order of frequency. Fittings and push-connect tubing lead the list, followed by housing end caps, storage tank base connections, and filter housing seals after a filter change.

Fittings and tubing leak most often because the tubing was not pushed fully into the fitting. Tubing needs to insert roughly three-quarters of an inch to seat properly against the internal O-ring. A shallow insertion never forms a complete seal.

Tubing that has been removed and reinserted repeatedly develops small scratches over time. These scratches eventually run deep enough that the O-ring can no longer seal against them, and the fix is simple: replace the scratched section of tubing.

Membrane housing leaks usually appear at the end caps after a membrane change. A dry, stretched, or damaged O-ring on the end cap is the most common cause.

Lubricate every O-ring with a silicone-based lubricant during each membrane or filter change. Do not reuse an O-ring that shows visible cracking or has stretched out of shape.

Storage tank leaks typically pool at the base of the tank. This points to a compromised bladder inside the tank rather than a simple fitting issue.

A tank with a failed bladder cannot hold pressure and needs replacement. Tightening the fittings where the tank connects to the system stops leaks caused by a loose connection, but it will not fix a torn bladder.

Filter housing leaks occur when a housing is not sealed properly after a filter change, or when the housing itself has cracked. Inspect housings for hairline cracks each time a filter is replaced, and confirm the O-ring is seated evenly around the housing before tightening it back into place.

Leaks carry more weight on a commercial system than on a residential one. A food and beverage plant, a hospitality operation, or a healthcare facility treats an RO leak as both a water loss and a potential contamination concern, which makes a prompt repair a higher priority than it would be for a small household drip.

Why Has My Reverse Osmosis Water Quality Changed?

A change in reverse osmosis water quality, whether cloudy water, unusual taste, or rising TDS readings, almost always means the rejection rate has dropped below its rated specification, or a bypass is allowing unfiltered water through.

Rejection rate decline is the most common cause of changed water quality. A properly functioning system rejects 95 to 99 percent of total dissolved solids from the feed water. Once rejection drops below 90 percent, the difference becomes noticeable in the water itself, not just on a test strip.

This decline usually means the same fouling, scaling, or aging process covered earlier in this guide has progressed further. A TDS reading taken now and compared against the system's baseline reading confirms how far rejection has slipped.

Taste and odor changes point to a different cause: chlorine breakthrough. This happens when an upstream chlorination system or a spent carbon pre-filter fails to remove chlorine before the feed water reaches the element. Chlorine exposure degrades it permanently, which is why catching breakthrough early matters.

A well water source carrying dissolved gas, such as hydrogen sulfide, produces a distinct rotten egg smell that concentrates as it passes through the system. This kind of odor issue needs correction in the pre-treatment stage, not at the membrane.

Stagnant water sitting in the storage tank or lines for an extended period can also develop an off taste. Flushing the system clears this without pointing to an actual component failure.

Cloudy or particulate water usually means unfiltered water is bypassing the filtration element rather than it failing outright. A leaking bypass valve or a cracked O-ring at the housing end cap allows raw feed water to blend with treated permeate.

Inspecting the bypass valve and the housing seals rules out this cause before assuming a full membrane failure.

Regular testing catches all three of these problems before they become obvious to the end user. A water test kit measuring TDS on a consistent schedule flags a slipping rejection rate weeks before taste, odor, or clarity changes would otherwise be noticed.

Why Is My Reverse Osmosis System Making Unusual Noise?

Unusual noise from a reverse osmosis system points to one of four causes: a struggling booster pump, air trapped in the drain line, a restricted flow path, or loose mechanical components vibrating against the mounting frame.

Humming or buzzing usually comes from the booster pump or transformer working harder than it should. Electrical strain or mechanical wear inside the pump produces this sound as the motor struggles to maintain output.

Gurgling sounds typically originate in the drain line during the system's normal flushing cycle. An air gap in the drain line configuration often adds to this noise.

Whistling or high-pitched sounds point to restricted water flow, usually from a clogged pre-filter or an over-tightened fitting somewhere in the line. Restricted flow forces water through a narrower path than the system was designed for, and that narrowing creates the pitch.

Vibrating noises come from loose mounting or an unbalanced pump. A system placed on an uneven surface transmits far more vibration into the surrounding structure than one mounted on a stable, level base.

Placing the system on anti-vibration pads reduces vibration noise significantly. Tightening loose fittings addresses whistling caused by restricted flow, and inspecting the pump directly resolves persistent humming that does not go away on its own.

Some operating noise is normal for any reverse osmosis system. A sudden change in the sound a familiar system makes, rather than the presence of noise itself, is the signal worth investigating.

How Often Should Reverse Osmosis System Components Be Maintained?

Reverse osmosis systems need pre-filter replacement every 6 to 12 months, membrane replacement every 2 to 3 years, storage tank inspection annually, and continuous monitoring of feed pressure and TDS rejection to catch fouling or scaling before failure occurs.

Upstream equipment protects the filtration element and extends its service life. A water softener installed ahead of the system removes hardness minerals before they ever reach it, cutting scaling risk substantially.

A sand filter installed for turbidity control removes larger particles that would otherwise shorten pre-filter life. Chlorination and UV disinfection systems each play a role in controlling biological growth in the source water, though neither replaces the element's own filtration function.

Chemical dosing systems maintain antiscalant levels automatically, which keeps dissolved minerals suspended in solution instead of crystallizing on the surface. Keeping a written log of each maintenance action, including the date and the reading recorded, makes it easy to spot a trend before it becomes a failure.

A system maintained on this schedule rarely surprises its operator. Most emergency service calls trace back to a skipped pre-filter change or an ignored TDS trend rather than a sudden, unpredictable failure. See Top 7 Most Replaced Water Treatment Parts and How to Keep Them Stocked and Choosing the Right RO Membrane for Your System for a deeper dive on stocking and selection.

When Should You Contact a Water Treatment Professional?

Contact a water treatment professional when pressure, flow, and tank tests all point to a component failure that cannot be accessed safely, when a commercial system affects production, or when a technical support case requires an on-site visit.

AXEON Supply's technical support team handles installation assistance, general troubleshooting of systems and components, clarification of system requirements, and interpretation of error messages for AXEON products. The team also verifies abnormal operation, offers preventative maintenance recommendations, and helps resolve suspected defects.

Technical support does not include on-site visits, troubleshooting of non-AXEON products, or training on the basics of water treatment beyond documented product parameters. Knowing this in advance sets accurate expectations for what a support call can and cannot resolve. Full details are in AXEON's Technical Support Policy.

Before calling, have the following ready: the AXEON account number, the system model and serial number, the current source water quality analysis with water temperature, and a clear description of the issue, the application, and the products installed.

AXEON Supply's technical support team can be reached at 1-800-320-4074, Monday through Friday, 7:30 AM to 4:30 PM PST. Every call receives a case number for future reference, which is worth recording for any follow-up.

Frequently Asked Questions About Reverse Osmosis Troubleshooting

What are the most common reverse osmosis system problems?

Most reverse osmosis system problems fall into four categories: fouling, scaling, mechanical failure, and chemical attack. Fouling and scaling build up gradually and reduce output over time, while mechanical and chemical failures tend to appear suddenly and require component replacement.

How do I troubleshoot a reverse osmosis system step by step?

Check feed pressure first, since most output problems trace back to pressure below the required minimum. Next, inspect pre-filters and test rejection rate, then check storage tank precharge. This sequence isolates the failing component fastest.

What PSI should a reverse osmosis system run at?

Most reverse osmosis systems require a minimum of 40 PSI of feed pressure to operate correctly. The optimal range for consistent performance runs from 60 to 80 PSI.

How long do reverse osmosis membranes last?

A reverse osmosis membrane typically lasts 2 to 3 years under normal operating conditions. A rejection rate that falls below 90 percent before this interval signals early replacement is needed. See What Factors Determine the Lifespan of Commercial Reverse Osmosis Membranes for a deeper breakdown.

Why is my reverse osmosis system water cloudy?

Cloudy water usually means unfiltered water is bypassing the membrane rather than the membrane failing outright. A leaking bypass valve or a cracked O-ring at the housing end cap is the most likely cause.

Feed pressure and rejection rate are the two checks that solve most reverse osmosis problems. Confirm pressure sits in the 60 to 80 PSI range, then confirm rejection stays above 90 percent, and the majority of possible causes are already eliminated before any component gets replaced.

For readers who have identified a failed part, AXEON Supply's Reverse Osmosis Systems collection carries replacement membranes, pumps, valves, and tanks built to the same specifications covered in this guide.

Account holders with a problem that these steps do not resolve can request a quote or reach AXEON Supply's technical support team directly for further diagnosis.