my ispring t32m drain line keeps running non-stop, even overnight. is it supposed to do that?

Diagnosis

The iSpring T32M is a pressurized storage system designed to shut off via an Automatic Shut-Off Valve (ASO) once the tank reaches its maximum pressure. If the drain line is running continuously, it indicates a failure in the pressure-sensing loop. The system is stuck in a "fill cycle," where water continues to flow through the RO membrane and out the waste line because the ASO valve never receives the signal that the tank is full. This happens when the internal pressure of the storage tank does not reach the required threshold to push the ASO valve closed. The most common root cause is insufficient incoming water pressure. The T32M requires a minimum of 40-45 PSI to effectively push water into the pressurized bladder of the tank and trigger the shut-off mechanism. If your home pressure is 35 PSI or lower, the system will struggle to overcome the back-pressure of the tank, causing the ASO valve to remain open indefinitely. Alternatively, this can be caused by a ruptured internal bladder in the T32M tank or a fouled check valve that allows pressure to bleed back into the membrane, preventing the system from ever reaching the "cutoff" point.

How to Fix It

To resolve a non-stop drain line, follow these precise steps to isolate and fix the pressure failure:

1. Measure Incoming Pressure: Install a gauge on your cold water supply line before the RO system. If the reading is below 40 PSI, the system cannot shut off naturally. You must install a permeate booster pump or a home-wide pressure regulator to increase PSI.
2. Test the Tank Pre-Charge: Turn off the water supply and open the RO faucet until the water stops flowing. Locate the air valve (Schrader valve) on the bottom or side of the T32M tank. Use a tire pressure gauge to check the air pressure. It should be between 7 and 10 PSI when the tank is empty.
3. Adjust Tank Air Pressure: If the pressure is below 7 PSI, use a bicycle pump or compressor to add air in small increments. Do not exceed 10 PSI, as over-pressurizing will prevent the tank from filling with water.
4. Inspect the ASO Valve: Locate the four-way Automatic Shut-Off Valve (the small plastic block where four tubes connect). Gently press the tubing into the ports to ensure they are seated fully. If the valve is cracked or the internal diaphragm is stuck, replace the ASO valve entirely.
5. Verify Check Valve Operation: Ensure the check valve (usually located at the exit of the membrane housing) is clicking shut. If you hear a "hissing" sound coming from the membrane housing while the system is idle, the check valve is leaking, which keeps the ASO valve open.

If That Didn't Work

• Replace the RO Membrane: A severely fouled or clogged membrane can create too much resistance, preventing the system from reaching the pressure needed to trigger the ASO valve. If the "pure water" production has slowed to a trickle while the waste line runs, replace the membrane element.
• Check for Kinks in the Drain Line: Ensure the waste line is not pinched or running uphill. If the waste water cannot exit freely, it can create back-pressure that interferes with the ASO valve's ability to sense the correct pressure differential.
• Swap the T32M Tank: If the tank feels heavy (full of water) but the drain line is still running and the air pressure is correct, the internal bladder may have a "pinhole" leak. This allows water into the air chamber, ruining the pressure differential. Replace the tank if it fails to hold air pressure for 24 hours.
• Install a High-Pressure Switch: For systems in low-pressure areas, replace the mechanical ASO valve with an electronic high-pressure switch and a solenoid valve. This allows the system to shut off based on a lower, customizable pressure threshold.

Heads Up

• Avoid Over-Pressurizing: Never pump the T32M tank above 10 PSI when empty; doing so will occupy the space meant for water, drastically reducing your usable gallon capacity.
• Monitor Filter Life: Replace the three pre-filters every 6 months. Clogged pre-filters drop the pressure reaching the membrane, which can trigger the same "non-stop drain" symptom.
• Check for Leaks: Always use food-grade Teflon tape on NPT threaded connections to prevent micro-leaks that can drop the system pressure just enough to keep the ASO valve open.
• Saddle Valve Warning: If you are using a saddle valve for the water source, be aware that these often restrict flow and drop PSI. Replacing a saddle valve with a T-adapter significantly improves shut-off reliability.