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How To Troubleshoot Your Undersink Reverse Osmosis System

by Mark Timmons March 30, 2020 16 Comments
Under the Sink Reverse Osmosis System

Frequently Asked Question:

We just changed our whole reverse osmosis by buying a new tank and new filters and a membrane (supposedly made in the USA). The filters and membrane we bought now are the same as the ones used previously. The problem we have now is that the TDS measures high… way higher than the tap water we have, which usually measures between 159 and 162. Our reverse osmosis's TDS is now over 200. We had readings from 800+ to 150+ and now to over 200. The water tastes really good, though, like fresh. I grew up on the farm in eastern Europe, and we only drank fresh well water, so I know what fresh tastes like.

What could make the TDS numbers so high? Our reverse osmosis is a 5 -Stage as I don't see the point of adding all those expensive, extra filters that don't make any sense. We do have mineral drops that we could add to our water, but I concentrate on healthy food to get them from first.

Under the Sink Reverse Osmosis System

Typical 5-Stage RO System

This is a common question that we get several times a week. I am going to list some things that can be a problem when changing your RO filters, although I think that #1 is likely your problem. Here is a list of issues that can impact your water quality when changing your filters and/membrane:

1. RECONNECT LINES PROPERLY: When you change the RO filters and/or membrane, sometimes you forget how to reconnect the tubing. I suggest taking pictures before you remove any tubing so that you can reconnect it back properly.

2. PUSH THE MEMBRANE ALL THE WAY IN: If you have a standard 5-Stage RO like the one pictured above when you disassemble the membrane housing and pull out the membrane (which you usually have to use pliers to do), frequently people fail to push the membrane in securely. There are two o-rings on the end where it gets pushed in. You should lubricate the o-rings with a light layer of silicone (which we include in our filter packs) - never use Vaseline as it will deteriorate the rubber o-rings. You can take a quarter and put it on the end of the membrane where you push it in.

3. THOROUGHLY RINSE THE SYSTEM: It is common to see cloudy water from carbon fines when changing the filters. I suggest letting the tank fill up and then open the faucet and let the water run until it stops. Repeat that two more times By the way, it may take several hours to fill the tank. Some people complain of air bubbles in the water. Air readily travels through an RO membrane, so if your water supply has a lot of air, you will see bubbles. They float the top and dissipate after a few seconds. Most people agree that dissolved oxygen makes water taste better.

4. NO WATER COMES THROUGH THE SYSTEM: Several things can cause this, including not turning the inlet valve or tank valve back on (duuuuhhhh!). Your flow restrictor (located at the drain line on the membrane) could be plugged. Always match your flow restrictor to your membrane size, and if you change membrane sizes (higher or lower GPD), make sure to match the flow control.

5. TAKE THE WRAPPING OFF THE FILTERS: As obvious as that sounds, a few people fail to perform this obvious task.

6. CHECK YOUR AUTO SHUTOFF VALVE (ASO): You can have it installed backwards if you removed the tubing or just in turning the water on-and-off, the diaphragm can tear. The ASO is easily replaced and can be found HERE.

7. CHECK THE TUBING:Over the years, the tubing can get scratched or scored. If it has a deep scratch, you should just cut it short with “John Guest Snips” or replace the tubing.

Polyethylene Tube Cutter - TSNIP

8. NO PRESSURE IN YOUR PRESSURE TANK: I advise replacing the tank every 5 years anyway, but if you have lost pressure, do not just add air. The air leaked out some way - just replace the tank as the odds are the bladder is bad.

9. SANITIZE THE SYSTEM: We have direction in our filter packs. Be sure and sanitize the system after each filter change. We also have lots of videos to help your troubleshoot and/or install the systems:

10. CONSIDER A OPERATION & MAINTENANCE KIT: Our kits have most of the things you need to replace or repair parts on your RO system. It can save you a lot of trouble later.

11. LEGENDARY TECHNICAL SUPPORT: If all else fails and you have exhausted the above tips, you can call us at 800-608-8792 and ask for our Legendary Technical Support. Did I mention that it is legendary?

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July 23, 2020 Jon

I have seen guides on sanitation of RO systems when changing fiilters. The pre-filters are removed, the post filters are left in then sanitizer is run through the system and all filters are changed after the fact. But what about sanitizing a newly installed system? In this case, post filters are not yet inserted, however what should be done with the post filters? Can or should sanitizer be run through them?

July 28, 2020 Francisco Gonzalez

After replaceing all the filters (5 stage) including gthe membrane, there is a substantial increase in water volume at the dispenser / fill point.
The water appears clean, no solids, no odor. Why such an increase in volume output?

July 28, 2020 Mark Timmons

1. Either the filters were really plugged; or 2. You do not have the membrane pushed all the way in.

December 29, 2020 Harriman, William Harriman, William

What should the pressure be in the storage tank?

December 30, 2020 Mark Timmons

5-7 psi

January 02, 2021 Mike Karey

Changed four filters in 5 stage system, didn’t change osmosis filter as only been one year. Hooked everything up exactly the same, tank is plum full but no pressure through the faucet. Is my system air locked? Or is this normal?

January 10, 2021 Mark Timmons

How much air is in the tank? Shut off the tank and disconnect it. Does water come out when you turn the valve back on? If not, you have a bad bladder.

August 19, 2021 Joe ODonnell

We have a 5 stage ro system and have changed all the filters and membrane but after all that the tds numbers start low and progress higher and higher nut sure what’s happening. If I fill the tank up completely and shut off the water it is fine till it empty and then I repeat the process and it works fine, but if I leave the water on to the system the tds gets worse and worse??

August 20, 2021 Mark Timmons

If it is a permeate pump RO, that is the nature of the beast. It’s called TDS Creep and you just have to drain the tank periodically. If not, you should replace your check valve… and while you are at it, replace your ASO valve and flow control.

September 14, 2022 Bill

I have a Frizzlife PD600 and suddenly the built-in TDS which constantly monitors my water is no longer displayed. It was showing 15 since we’ve had it and now display shows as – - with NO NUMBER displayed.

October 23, 2022 Mark Timmons

Sorry, but I have never heard of that product and we do not service it.

November 10, 2022 Jane

I have recently changed the RO machine’s membranes which has led to bubbling of the water,what is the solution to that?

November 12, 2022 Mark Timmons

That is generally air in the system. Dump a couple of tanks of water, and it should go away.

April 10, 2023 Rob A

Why has the flow from my four-month-old RO system slowed and stopped?

April 11, 2023 Mark Timmons

I do not know. I cannot see it from here. It could be a number of things, but I would bet on something plugging up. Call our tech support department and they will help you.

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