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What to Do When Drain Water Runs All the Time

Our RO systems are designed to shut off automatically when the tank is full. When the RO fails to shut off after tank is full, drain water will continue to run, possibly depleting the pre-filters, the membrane, and costing high water bills.

If the drain water is running non stop, the input water pressure may be too low (below 40psi). Not enough pressure to shut off the RO at all,  check input water pressure. If pressure is below 40psi, you may need to switch to Booster-Pumped RO model.

Another cause may be due to defective shut-off valves. Do a shut-off test to determine which valve is defective. The Auto-Shut-Off (ASO) valve is located at Point C. The Check Valve is located at Point E. Refer to Figure.15 on page 26 in owners manual.

These two valves control the ROs shut off function. If one of these valves fails (valve worn out, clogged, or defective), the system cannot shut off.  The drain water will keep running non-stop. Please do test #1 and test #2 below to determine if the RO can shut off, and if the valves are OK.

Test #1. Testing system shut off:

  • Draw 2-3 glasses of water from spigot. RO will start making water to fill tank.
  • Turn OFF the tanks valve to mimic tank full. To turn off the tank ball valve, simply turn the blue handle 90 degrees.
  • If your RO feeds multiple output points (icemaker, bathroom, etc), shut OFF those lines.
  • Wait for 3- 5 minutes, then check to see if the drain water stops running.
  • Check drain water by either listening or actually pulling out the drain line to look at it.  If drain water stops running –> The RO is shutting off properly. Both the ASO valve and the Check Valve are working fine. Stop testing.
  • If drain water continues to run –> Then either the Check Valve and/or the ASO valve is defective. Proceed to Test #2.

Test #2. Testing ASO and Check Valve:

  • Make sure there is some water in the tank (tank not empty).
  • Remove the Black drain line from the drain saddle (so you can check drain flow drainage).
  • Turn OFF the Cold feed water supply.
  • Turn ON the tank valve.
  • Check the Black drain line to see if there is any water draining out from this line.
  • If water does drain out from the black line  then this water is coming from the storage tank. This means the Check Valve is broken, it is allowing the water in the tank to back flow out into the drain line.
  • If no water drains out from the black line (no drain water running) –> That means the Check Valve is OK. The ROs non-shut off is caused by a defective ASO valve, not caused by the Check Valve.

If the issue was not addressed, please contact us at:
800-880-4808, or

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