# whole house reverse osmosis troubleshooting

> Low output, high TDS, or constant drain flow? Check pretreatment, pump pressure, and membrane rejection. See causes and $20-$600 fixes.

Canonical: https://watertreatmentpro.com/whole-house-reverse-osmosis-troubleshooting/

Last updated: 2026-11-09

Whole house RO problems are usually clogged pretreatment, low feed pressure, a failed pump, or a membrane that has lost rejection. Measure pressure and TDS before replacing anything. A $600 membrane is the last suspect, not the first.

## Two numbers explain most failures

Feed pressure and rejection percentage tell you where the system stands.

Feed pressure should be 60-80 psi at the membrane inlet. Below that, production falls and rejection drops, because the membrane needs pressure to overcome osmotic back-pressure.

Rejection is feed TDS minus product TDS, divided by feed TDS. At 400 ppm feed and 32 ppm product, that is 92 percent. Below 80 percent, something has failed.

Record both monthly. A trend is more useful than a single reading.

## The symptom table

| Symptom | First check | Cost |
|---|---|---|
| Low output | Pretreatment, feed pressure | $15 - $120 |
| High product TDS | O-rings, membrane | $10 - $600 |
| Constant drain flow | Shutoff valve, float | $40 - $150 |
| Pump noisy | Booster pump bearings | $300 - $700 |
| Water tastes off | Post-carbon, storage tank | $30 - $120 |
| Pressure at taps low | Repressurization pump | $400 - $900 |

Low tap pressure with good production points at the repressurization pump or the pressure switch, not the membrane.

## Diagnose in this order

1. Read feed pressure at the membrane inlet.
2. Read product TDS and calculate rejection.
3. Inspect and replace prefilters if due.
4. Check the booster pump for noise and consistent output.
5. Confirm the shutoff valve stops flow when storage is full.
6. Inspect membrane housing O-rings for damage.

Doing this in order prevents the most expensive mistake in the category: replacing a membrane while a $25 prefilter was the actual fault.

### Reading rejection correctly

Take the feed sample before the membrane and the product sample from the permeate line, not from the storage tank.

Tank water can pick up TDS from the bladder and the fittings, which makes a healthy membrane look worse than it is.

Let both samples reach room temperature and rinse the meter between readings.

A rejection number that moves by two points is noise. A drop of five points or more is a trend worth acting on.

## Pretreatment failures

A clogged sediment prefilter reduces feed pressure and starves the membrane. Replace it every 3-6 months.

An exhausted carbon stage lets chlorine reach the membrane, which destroys it permanently. That failure shows as a sudden rejection drop with no other symptom.

Hardness scales the membrane, and iron fouling is irreversible. Both are upstream problems that no membrane cleaning solves.

## Pump problems

The booster pump provides membrane pressure. A pump that is noisy, hot, or cycling is failing.

Check the pressure at the membrane inlet while the system runs. A pump that cannot reach 60 psi is not doing its job.

The repressurization pump moves water from storage to the house. Short cycling points to a waterlogged tank or a failed pressure switch.

## Storage and controls

A system that runs constantly is not reaching its shutoff point. Check the float or level switch, then the shutoff valve.

A tank that will not hold precharge has a failed bladder. Replacement is $400-$1,200.

A pressure switch set too high keeps the pump running without building pressure, which burns the motor. Set it 5-10 psi below the pump's maximum and confirm it shuts off with the faucet closed.

## When to replace the membrane

Replace when rejection stays below 80 percent after prefilters and O-rings are confirmed good.

Replace when production falls by a third at normal pressure and temperature.

Replace when the membrane is 2-3 years old and the water quality has slipped, even if rejection is borderline.

### When the system is undersized

A whole-house RO sized for 150 gallons per day in a household using 250 will always look like a failing system.

The symptom is a storage tank that never catches up. Production runs constantly, the pump cycles, and the house still runs out during morning showers.

Check the arithmetic before replacing parts: daily household gallons against membrane output at winter temperature.

Cold water halves output, so a system rated at 300 GPD at 77°F produces about 150 GPD at 50°F. A system sized on the summer number is undersized for half the year.

The fix is more membrane area, more storage, or both. Storage is usually cheaper, and an 80-gallon tank at $400-$1,200 solves more complaints than a second membrane.

If the well cannot supply the feed and the concentrate, the system needs a storage tank and a booster pump upstream, which is a different project and a $1,000-$2,500 line item. Test the well's recovery rate before adding membrane area, because a bigger membrane on a weak well just runs dry. [Whole house reverse osmosis cost](https://watertreatmentpro.com/whole-house-reverse-osmosis-cost/) covers the sizing math.

## Prevention

Change prefilters on schedule. Test rejection monthly. Keep the booster pump pressure in range. Sanitize annually. Check the storage tank precharge with the tank drained once a year, because a waterlogged tank makes a healthy system look weak.

Write the membrane install date on the housing, and note the rejection percentage beside it. Two numbers on a sticker replace a lot of guessing when production drops a year later. A three-year-old membrane that is still at 90 percent rejection is a bonus, not a plan. [Whole house reverse osmosis maintenance](https://watertreatmentpro.com/whole-house-reverse-osmosis-maintenance/) covers the schedule, and [change RO membrane](https://watertreatmentpro.com/change-ro-membrane/) covers the replacement.
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