Why Is My RO Running Continuously After a Kit Change?
 

An RO purifier keeps running after a kit change for one of two reasons. Either it is normal, because the new filters and the empty tank need time to fill, or something is stopping the system from reaching shut-off pressure. The usual faults are air in the lines, a leak, a faulty auto shut-off (ASO) valve, low inlet pressure, a wrongly fitted tube or a wrong tank pre-charge.

A purifier that runs for a few hours after a kit change is usually fine. One that runs all day and all night, or keeps sending water to the drain, needs checking.

 

Is It Normal for RO to Run Longer After a Kit Change?

Yes, for a limited time. Right after you change the sediment filter, carbon filter or membrane:

• The tank may be empty or have been drained during service
• Air in the new cartridges and tubing slows the flow
• A new membrane needs to be flushed before it works at full output
   

Most domestic RO systems take 2 to 4 hours to fill an empty tank, and a little longer after a membrane change. If the purifier still does not shut off after about 6 hours, treat it as a fault.

7 Causes of RO Running Non-Stop After a Filter Change
 

1. Air trapped in the system

Air in new cartridges and tubing lowers the pressure at the membrane and the tank. The system keeps trying to build pressure, so it does not shut off. Flushing the system (see below) solves it.

2. A leak after the service

A loose fitting, a missing or twisted O-ring or a half-seated cartridge can leak water or draw in air. If the purifier cannot build pressure, the ASO valve never closes. Look for drips, wet spots and hissing sounds.

3. Faulty or stuck auto shut-off (ASO) valve

The ASO valve closes the inlet when the tank is full. If it was bumped, blocked or damaged during the kit change, the purifier keeps running and often keeps sending water to the drain.

4. Tank pre-charge too low or too high

The storage tank has an air chamber that pushes water out. If the air pressure is wrong with the tank empty, the tank may take far too long to fill, or never reach the pressure needed to trigger shut-off.

5. Low inlet water pressure

RO needs steady incoming pressure. Low pressure from the borewell, overhead tank or a partly closed valve delays the shut-off. The system can run for hours without getting a full tank.

6. Wrong or missing flow restrictor, or tubes fitted in the wrong port

If the flow restrictor was removed or replaced with a wrong rating, or if the tubes were connected to the wrong ports, the system loses pressure at the membrane and runs continuously.

7. Clogged or wrongly seated filters

         A choked sediment filter or carbon filter (or one fitted in the wrong order) cuts the flow. The membrane gets less water and the tank fills very slowly, so the system seems never to stop.

How to Fix an RO That Keeps Running After a Kit Change
 

1. Run the system for one full cycle and observe. Note how long it takes to stop. Give it about 4 to 6 hours.
2. Flush out the air. Open the RO tap and let water flow until it runs smoothly with no spurting.
3. Check for leaks. Dry every joint with a tissue and watch for dampness. Tighten fittings and check each O-ring.
4. Check the tubes. Make sure every tube is fully pushed in and in the correct port. Gently tug to confirm.
5. Check the cartridge order and fit. The usual order is sediment, then carbon, then membrane. Each cartridge should be fully seated.
6. Check the tank pre-charge. Empty the tank and check the air pressure as per your manual. Re-pressurise if it is low.
7. Check inlet pressure and valves. Make sure the inlet valve is fully open and the supply is steady.
8. Check the ASO valve and flow restrictor. If water goes continuously to the drain, one of these may be at fault. This is best handled by a technician.

Using matched, genuine parts avoids most of these problems. See the complete RO filter kit and the individual parts:

• Sediment Filter to protect the membrane from sand and silt and keep the flow steady
• RO Carbon Filter for chlorine, odour and taste
• RO Membrane for TDS reduction and the main purification

How to Tell Normal Running From a Fault

When to Call a Technician

Get help if:

• The purifier does not shut off after 6 to 8 hours
• Water runs constantly to the drain
• There are visible leaks or a persistent hissing
• The tank does not fill even after flushing and checking pressure
• The purified water has a changed taste, smell or TDS
   

A continuously running RO wastes water, strains the pump and wears out the new membrane early. If your supply is hard or carries a lot of sediment, consider the RO water purifiers range or a water softener to protect the new kit.

How to Prevent This After Your Next Kit Change
 

• Flush every new cartridge and membrane before using the water
• Replace filters in the right order and on schedule
• Keep spare O-rings and apply food-grade silicone
• Check the tank pre-charge at every service
• Use a sediment pre-filter for borewell water
   

More service guides are in the Pearl Water blog.
 

Frequently Asked Questions

1. Why does my RO not stop after changing the filter?
The new filters and the empty tank need time to fill, and air in the lines slows the pressure build-up. If it continues beyond 6 hours, check for leaks, the ASO valve, the tank pre-charge and the inlet pressure.

2. How long should RO run after a kit change?
Usually 2 to 4 hours to fill an empty tank. After a membrane change it can take a little longer.

3. Why is my RO draining water continuously after the kit change?
The ASO valve may be stuck or damaged, the flow restrictor may be missing or wrong, or the tubes may be in the wrong ports.

4. Can low water pressure make RO run non-stop?
Yes. Low inlet pressure prevents the system from building the pressure it needs to shut off.

5. Is a continuously running RO harmful?
It wastes water, raises the electricity use and puts extra load on the pump and the membrane, so it should be fixed rather than ignored.