RO 45 - Troubleshoot Guide: No Shut-Off

Test ASO & Check Valve

When the wastewater from your RO runs non-stop all day, and cannot shut off even when the tank is full.

3 possible causes:

  • Broken or Insensitive Auto Shut Off (ASO) Valve
  • Broken or Clogged Check Valve
  • Possible additional outlet is leaking water. Such as, humdifier, hot water dispenser or ice-maker.

You can do the test below to find out which part is broken or insensitive.

Test Check Valve and ASO Valve:

  • Let RO fill up your tank.
  • Turn Off the Cold feed water supply to the RO.
  • Open the tank valve.
  • Remove the RO's Black drain line from the drain saddle (on your drainpipe).
  • Check this Black line to see there is any water-draining out.
  • If there is water draining out from this line --> This means the Check Valve is bad. If has failed to shut off.

It is allowing the water in the tank to back flow out into the black drain line.

Solution: Replace Check Valve (see diagram point E) - If there is No water draining out from this black line -->

This means the Auto Shut Off valve is bad, and the Check Valve is OK.

Solution: Replace the ASO Valve (see diagram Point C)

Order Check Valve or ASO online at this link:

Item# Check Valve

Item# ASO

Check 2nd output line for leaks:

If your RO feeds a 2nd or 3rd output point, check those lines and fittings for any possible pressure leakage. Any slight leakage in the line will cause the RO to not shut off.

RO-45/RO-90 Head Diagram

Please Note:

RO shut-off failed: Depletes stages 1, 2, 3 Prefilters

Since your RO could not shut off, input water has been going thru the stages 1,2, 3 prefilters constantly. If this has gone on for more than 1-2 months, chances are these prefilters are depleted from the continuous draining of water in the last few months. So we think you should change the 3 prefilters now if possible, so they can protect the membrane.

Reminder: Check Membrane with TDS meter!

If you have a TDS water tester, you can check the stage-4 Membrane to verify membrane is still good.

Reminder: Yearly Pre-filter Change Important!

It's important to change the 3 prefilters at least every 12 months. They protect the stage 4 Membrane, which is the heart of the RO system.

If you forget to change the prefilters timely, they'll get over-depleted or over loaded, this will damage the Auto-Shut-Off valve and the Stage-4 Membrane. So it's very important to replace the 3 prefilters once a year.


End of Test

RO System - Membrane & Filter Change Schedule

There are 5 filter cartridges on your under-sink RO system

Stages-1, 2, & 3 Pre-filters:

  • Change every 12 months.
  • Cost: $39 per set (1 sediment, 2 carbons) same for all models
  • Order Item# FILTER-SET

Stage 4 RO membrane:

  • Change every 3-5 years depending on input water quality.
  • Cost: $65 (for RO45, RO-PUMP models)
  • Cost: $85 (for RO90, RO-PERM models)
  • Order Item# MEM-45 or MEM-90

Stage 5 polish filter:

  • Changed once every 3-5 years.
  • Cost: $15 (same for all models)
  • Order Item# 5-TCR

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