Yeah, this one's common. A constant drain flow usually means the auto-shutoff valve on the RO head isn't closing properly.
- First, make sure your storage tank is actually full. Shut the tank valve and open the faucet. If no water comes out, the tank is empty and the problem is different.
- If the tank is full, tap lightly on the auto-shutoff valve body. Sometimes sediment can keep it from seating.
- If tapping doesn't work, the valve diaphragm might be damaged or have debris. It may need replacement.
If that didn't work: Check the drain saddle. The needle valve in the kit controls drain flow rate. If it's opened too wide or is faulty, it can cause excessive drainage. Adjust it slightly.
Heads up: A constantly running drain wastes water and can overwhelm your plumbing. Get this fixed. Also, never install the system where it could freeze—that'll wreck valves fast.