apec roes-50 won't shut off, keeps running and dumping water down the drain. help?

Diagnosis

The APEC ROES-50 utilizes an Automatic Shut-Off (ASO) valve that relies on a pressure differential to stop the flow of water. When the storage tank reaches approximately 60-70% of the incoming line pressure, the ASO valve closes the feed water inlet, stopping the production process. If your system is constantly dumping water down the drain, it means the ASO valve is never receiving the signal to close, causing the membrane to continuously process water and send the brine (waste) down the drain indefinitely. This failure typically stems from one of two root causes. First, the diaphragm in the pressurized storage tank may have ruptured or lost its air charge. If the tank cannot build back-pressure, the ASO valve stays open forever. Second, the ASO valve itself—a small mechanical component located in the manifold head—may have a failed internal diaphragm or a clog, preventing it from sealing even when the tank is full. You can confirm a tank issue by lifting the tank; if it feels extremely heavy (waterlogged) but only a trickle of water comes out of the faucet, the air bladder has failed.

How to Fix It

To resolve a continuous drain issue, you must first determine if the tank is the culprit before replacing the valve. Follow these precise steps:

1. Test the Tank Pressure: Close the cold water feed valve. Open the RO faucet and let all the water drain out. Once the flow stops, lift the storage tank. If it is heavy, it is waterlogged.
2. Re-pressurize the Tank: Use a standard tire pressure gauge on the air valve (Schrader valve) located on the bottom or side of the tank. With the tank empty of water, the pressure should be between 7 and 10 PSI. If it is lower, use a bicycle pump or compressor to add air in short bursts until you hit 8 PSI.
3. Verify the ASO Valve: If the tank is properly pressurized but the system still won't shut off, you must inspect the ASO valve. This is the square-shaped component where the feed water enters the manifold.
4. Flush the Valve: Sometimes debris traps the valve open. Briefly close the feed water valve and open the RO faucet to create a vacuum, then snap the feed water valve open quickly to try and "shock" the diaphragm into place.
5. Replace the ASO Valve: If the issue persists, unscrew the ASO valve from the manifold using a crescent wrench. Install a replacement ASO valve, ensuring the O-rings are lubricated with food-grade silicone grease to prevent leaks.

If That Didn't Work

• Check for a Clogged Membrane: If the RO membrane is completely fouled or scaled, it cannot produce enough purified water to fill the tank and create back-pressure. If you haven't changed your membrane (the large center housing) in 2-3 years, replace it immediately. A failed membrane will cause the system to run indefinitely because the "full" pressure threshold is never reached.
• Inspect the Check Valve: There is a small one-way check valve located at the exit of the membrane housing. If this valve leaks, water from the storage tank flows backward through the membrane and out the drain, tricking the ASO valve into thinking the tank is empty. Replace the check valve if you notice the system starts draining again shortly after the tank is filled.
• Test Incoming Water Pressure: If your home's incoming water pressure is too low (below 40 PSI), the system may struggle to reach the shut-off threshold. Install a permeate pump or a booster pump to increase the pressure entering the membrane.
• Examine the Drain Line: Ensure the black drain line is not kinked or restricted. While a restriction usually slows the flow, an extreme blockage can sometimes cause erratic pressure readings within the manifold, preventing a clean shut-off.

Heads Up

• Air Pressure Warning: Never add air to the storage tank while it is full of water; you must drain the water first, or you will get an inaccurate PSI reading and potentially damage the bladder.
• Filter Schedule: Replace your Stage 1, 2, and 3 sediment and carbon filters every 6-12 months. Clogged pre-filters reduce the pressure reaching the ASO valve, which can lead to longer run times and wasted water.
• Leak Check: After replacing the ASO valve or adjusting the tank, wipe all connections with a dry paper towel. Even a tiny "weeping" leak at the manifold can prevent the system from reaching the pressure required to shut off.
• Tank Positioning: Always keep the storage tank upright. Laying it on its side can cause the internal bladder to shift, leading to premature failure and waterlogging.