Reverse Osmosis Repair
A reverse osmosis system is a loop of five cooperating parts: feed pressure pushes water through prefilters and the membrane, the storage tank holds the product on an air charge, the automatic shutoff valve decides when to stop making more, and the flow restrictor meters the reject stream to drain. Every RO complaint (the empty tank, the endless drain trickle, the flat taste) is one of the five misbehaving, and two instruments identify which: a pressure gauge and a TDS meter.
Signs You Need This Service
The complaint list, decoded:
- The empty tank. A faucet that gives a glass and dies: the tank's air charge lost, its bladder failed, or production upstream too slow to refill it. The most common RO complaint, with three different owners.
- The endless drain trickle. Water running to drain long after the tank is full: the shutoff valve or check valve no longer closing the loop, quietly spending water through every idle hour.
- Taste gone flat or wrong. Product TDS creeping toward feed TDS: the membrane exhausted or bypassed, or the postfilter past its service life adding taste back.
- Production slowed to a drip. Prefilters loaded, membrane fouled, or feed pressure below what the membrane needs: the trio that starves output, sorted by gauge and history.
- Leaks at the fittings. Push-fit connections and aging tubing weep at the worst spots. Under-sink drips get traced to the exact fitting before anything is replaced wholesale.
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This page covers diagnosing and repairing under-sink and similar point-of-use RO systems. Routine filter changes are maintenance the owner often keeps; this is the page for the system that stopped doing its job despite them, and for the honest call when a tired system argues for the installation page instead.
How a Plumber Diagnoses the Problem
The instrument-led sequence:
- Two TDS numbers. Feed water and product water measured. The rejection ratio is the membrane's report card and separates 'membrane done' from 'postfilter tired' in thirty seconds.
- Feed pressure read. Membranes need adequate driving pressure; a house running low starves the system into slow production and poor rejection, a plumbing fact no RO part will fix, routed to the pressure pages when found.
- The tank's charge checked. Air pressure measured empty against spec: low charge explains the one-glass faucet; water at the air valve convicts the bladder and retires the tank.
- The loop watched. Tank full, system observed: drain flow that never stops names the shutoff or check valve; the restrictor's condition gets verified alongside, since a wrong or clogged restrictor unbalances everything.
- Repair versus retire. Filters, membranes, tanks, valves and restrictors all replace individually. The loop rebuilds part by part. An aging system needing several at once meets the honest arithmetic against a modern replacement.
Frequently Asked Questions
Why is my RO tank always empty?
Three suspects: the tank's air charge has leaked down (recharge it), the bladder has failed (water at the air valve settles that, and it means a new tank), or production upstream is too slow to refill between uses (filters, membrane or feed pressure). The charge check and a production timing sort them in one visit.
Why does the system run water to drain constantly?
The automatic shutoff or check valve is no longer ending the cycle when the tank fills. The loop never closes, and reject water keeps running through every idle hour. Both are small replaceable parts; the constant trickle is the tell, and fixing it stops genuine water waste.
What causes high TDS in the product water?
An exhausted membrane no longer rejecting, a failed check valve letting product mix, or, mildly, a spent postfilter. The feed-versus-product measurement makes it arithmetic: healthy membranes reject the large majority of dissolved solids, and the ratio's collapse names the day the membrane retired.
Is weak RO faucet flow the system's fault or the house's?
Measure and know: adequate feed pressure with weak product points inside the system: filters, membrane, tank charge. Low feed pressure starves any RO regardless of parts, and that case belongs to the house's pressure diagnosis first. The gauge answers before any cartridge is bought.
Repair the RO system or replace it?
Every part replaces individually, so repair usually wins on single faults: a tank, a valve, a membrane. The math flips when age stacks failures: several tired parts at once on an old system can price past a modern unit with fresh certifications. The diagnosis shows both numbers plainly.
Diagnose the Loop
Describe the symptom (empty tank, constant drain sound, taste change, slow flow) and the system's age and last filter change. Two instruments and one visit usually name the part.
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