Yeah, this one's common. It's not supposed to run continuously. It usually means the system can't build enough pressure to shut itself off.
The top suspect is low incoming water pressure. If your home's PSI is below the required 45, the system just can't fill the tank and trigger the shut-off. You'll need a booster pump.
If your pressure is good, the Automatic Shut-Off Valve or the check valve might be defective. Here's a quick test:
- Get some water out of the RO faucet first, so the drain is actively flowing.
- Close the blue valve on top of the storage tank.
- Wait about five minutes, then check the drain line. If it's stopped flowing, your valves are probably fine and the issue is pressure.
- If it's still flowing, you've got a bad valve. Open everything back up, let the tank fill, then close the feed water adapter to cut the supply. Wait 15-30 minutes. If the tank empties, the check valve is the culprit.
HEADS UP: During the initial 1-3 hour tank fill, the drain will trickle. That's normal. It's the 4+ hour marathon runs that are the problem.