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How to Fix RO Auto Shut-Off Valve Not Working – Find Causes

RO auto shut off valve not working


The reverse osmosis system is the most useful appliance in our homes. It is a very useful and cheapest method to remove harmful chemical and biological contaminants from water. However, what if your reverse osmosis system is continuously draining wastewater? Does it annoy you?

If reverse osmosis drains a lot of wastewater, this could happen due to a damaged Automatic shut-off valve or stuck diaphragm. To fix the issue, ASO valve troubleshooting, reassembling, and replacing it can stop continuous draining. If this fails, replacing the Check valve and RO membrane can solve the issue.

In this blog post, we’ll explain how the Auto shut off valve works, the cause of its failure, and the troubleshooting of the ASO valve. We’ll also discuss in detail how to change or repair the ASO valve.

How does an RO auto shut-off valve work?

How does an RO auto shut-off valve work

An automatic shut-off valve controls the water entering the reverse osmosis system. It shuts off the water supply to the RO unit when the storage tank reaches ⅔ of the tank capacity or feed water pressure. In the same way, turn the water back on when tank pressure drops. The faulty ASO valve could cause a lot of wastewater to drain.

Why does the RO auto shut-off valve stop working?

When the ASO valve stops working, this could happen due to faulty plumbing or a damaged diaphragm in the valve. ASO valve failure can cause drain water to flow continuously and waste a lot of water.

1. Improper Installation

The faulty ASO valve installation can be the cause of its improper functioning. Loose or wrong tubing connection can make a lot of water to waste.

2. Faulty ASO Valve

A stuck diaphragm and its other component failure can cause water to turn off the water supply.

RO ASO Valve Troubleshooting Guide:

Troubleshooting ASO is 2 step process. This technique will help you to detect the actual cause of the RO system’s continuous draining.

Here are the steps that you need to follow to find and fix the problem.

1. Determine “ASO Valve” and “Check Valve” Failure

The first step in ASO valve troubleshooting is testing both the automatic shut-off valve and the check valve. The failure of any of these could be the cause of continuous draining. To test its malfunctioning, follow these steps.

  • Turn off the RO tank valve. It will replicate the tank is full to the RO system.
  • Disconnect the drain tube from the saddle clamp
  • Now Turn on the feed water source to the RO unit
  • If the drain doesn’t stop after 5-10 minutes or slows down, this will ensure the problem is in both of these valves.

2. Confirm the Faulty ASO Valve or Check Valve 

Now, we’ve determined the ASO or the Check valve could be the reason for continuous draining. This step will confirm whether the issue is with the ASO valve or the Check Valve. To confirm the actual valve failure, follow these steps.

  • Turn off the feed water to the RO Unit
  • Turn on the RO tank valve.
  • Now, it’ll confirm the actual valve failure.


If the water stops running through the drain tube, It confirms that the ASO valve failure is causing the issue. It could be due to the ASO valve diaphragm failure or a damaged ASO valve that is not shutting the valve off.

If the water continues running through the drain tube, It is happening due to the check valve failure. It makes water flow back into the membrane, and it all gets sent to the drain line and causes a lot of drain water to flow.

Verify Feedwater Pressure and RO Membrane is OK:

Before troubleshooting the ASO valve, ensure the feedwater pressure to the RO unit is between 45 to 55 PSI if the pressure is below the 45 PSI to prefilters. It can fail the RO membrane to filter out water and send it outlet. If this happens, all the water goes into the drain line continuously. 

If the feed pressure is between 45 to 55 PSI. Now, it’s time to check the RO membrane is in good condition. An expired or bad RO membrane restricts water from flowing through it. As a result, it will all get into the drain line.

How to Repair Automatic Shut-Off Valve?

How to Repair Automatic Shut-Off Valve

It is not advisable to repair the ASO valve to fix the continuous draining issue. However, to ensure the problem is due to miss plumbed valve, stuck diaphragm, or missed connection, it is advisable to reassemble it.

To reassemble it, here is the step-by-step to do this.

  • Turn off the tank and feedwater supply. 
  • Turn on the faucets to relieve pressure and drain the system. 
  • Disconnect the tubing of the ASO valve.
  • Unscrew it carefully. 
  • Wash out the dirt and debris from the ASO valve with a wire brush or sandpaper.
  • Screw it again carefully.
  • Re-connect the tubings again with the ASO valve. 
  • Turn on the tank and feed valve. 
  • Turn the faucet off, and Voila!

How Do I Replace the ASO Valve?

How Do I Replace the ASO Valve

Before you start to replace the ASO valve, ensure to disconnect the tubing carefully and fix the ASO valve by locating them with inlet and outlet valves. Once you are done, also ensure the tubings have been fitted and locked properly with the Automatic shut-off valve to avoid any leakage. 

Here is the step-by-step solution to do this.

  • Turn off the feedwater and tank valve.
  • Turn the faucet on to drain excess water from the tubings. 
  • De-attach the ASO valve with the inlet and outlet tubings. 
  • Connect the prefilter outlet valve to the High-Pressure Valve Inlet Valve (thicker) and RO membrane water inlet with the High-Pressure Outlet Valve.
  • Connect the membrane pure water outlet with the Low-Pressure Valve Inlet and connect the Low-Pressure Valve Outlet with the System Tee connector.
  • Now turn on the shut valve and tank valve. 
  • Shut off the faucet, and here you are done!


In this blog post, We explained the reason causes of the ASO failure and its troubleshooting in detail. We’ve also provided a step-by-step guide to repair and replace the RO auto shut-off valve. Additionally, We’ve discussed the important tips to verify before troubleshooting the system and other causes that make the RO system continue to drain.

If you are not tech-savvy or uncomfortable with any plumbing process. In that case, it’s best to seek professional assistance to troubleshoot the complete process. However, we advise you to contact the technical support of the manufacturer. 

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