Automatic shut off valves (ASO) in reverse osmosis filters have the role of turning off water production whenever the reverse osmosis tank is full. When the pressure in the RO tank reaches 2/3 of the pressure of the incoming water, the automatic shut off valve shuts off the incoming water. If the ASO becomes faulty or no longer operates, water in the reverse osmosis system will continuously run to drain making the system less efficient. When this happens, it becomes necessary to replace the ASO in your reverse osmosis water filter.

commercial reverse osmosis system

Water running to the drain may also be caused by other issues with your RO system. Our article on troubleshooting reverse osmosis water filter issues sheds light on other possible causes why water in your RO system keeps running to drain.

ASO valve replacement

ASO valves are universal and can be found in most modern reverse osmosis units. Their replacement also follows the same pattern for every RO unit that is equipped with such a device.

  1. Remove the reverse osmosis water filter unit from where it’s mounted so you can have easier access to the ASO valve. This can easily be done by disconnecting the quick connect push fittings.
  2. Locate the automatic shut off valve at the back of the RO system.
  3. Make sure to configure it exactly as the one that is installed on your RO filter. This means that you have to take into account the outlet and inlet ports and that one side of the ASO valve is bevelled, while the other is flat. Take this factors into account to set it up exactly as the ASO valve that’s installed on the system.
  4. Remove the tubing from the fitting on the ASO one by one and connect it to the new valve exactly in the way it was connected on the old ASO. If your tubing is of different colour than the one of the new ASO, it makes absolutely no difference, the most important thing is to configure and connect everything exactly how it was done on the old ASO.

Once you’ve managed to replace the ASO valve, test your system to see if water continues to run to drain. Apart from a defective shut off valve, water may keep running to drain also because you may be using the reverse osmosis membrane beyond its service life or because of a defective check valve. Replacing the reverse osmosis membrane or the check valve can solve the issue of water running to drain.