---
title: Why Is My RO Tank Not Filling?
description: RO tank not filling? Learn how to troubleshoot low pressure, clogged filters, membrane issues, and tank bladder problems.
---
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# Why Is My RO Tank Not Filling?
## An RO tank that won't fill typically points to low water pressure, clogged filters, a worn membrane, or issues with the tank's internal bladder pressure.
When your reverse osmosis tank stops filling, or fills painfully slowly, it's usually one of a handful of common culprits. The good news is that most of these issues are easy to diagnose and often simple to fix.
#### Common Causes
- **Low feed water pressure:** RO systems need at least 40 PSI to operate efficiently. Pressure below this threshold significantly slows production and may prevent the tank from filling altogether.
- **Clogged pre/post-filters:** Pre/post-filters are important for protecting your membrane and polishing RO water. But when they become saturated, water flow can drop dramatically. If it's been more than 12-18 months since your last filter change, this is a likely cause.
- **Worn or fouled membrane:** The RO membrane does the heavy lifting. Over time, it can become clogged with contaminants or simply wear out, reducing water production to a trickle.
- **Incorrect tank bladder pressure:** Your RO tank contains an air bladder that should be set to 7-11 PSI when empty. If the pressure is too high or too low, the tank won't fill or deliver water properly.
- **Faulty check valve:** The check valve prevents backflow from the tank. When it fails, water can flow backward through the system instead of filling the tank.
- **Auto-shutoff valve malfunction:** This valve stops water production when the tank is full. If it's stuck in the closed position, no water reaches the tank at all.
---
### How to Check Your Tank Pressure
Before replacing any parts, check your tank's bladder pressure. This is easily one of the most common and easily corrected issues.
- Turn off your water supply and close the tank valve.
- Open the RO faucet and let the tank drain completely until water stops flowing.
- Locate the air valve on the bottom or side of the tank (it looks like a bicycle tire valve).
- Use a low-pressure gauge to check the air pressure. It should read 7-11 PSI on an empty tank.
- If the pressure is low, use a bicycle pump to add air. If it's too high, release air until you reach the correct range.
- Close the faucet, open the tank valve, and allow the system to refill.
#### Quick Troubleshooting Steps
If adjusting the tank pressure doesn't solve the problem, work through these steps:
- Check your home's water pressure with a gauge at a nearby faucet. If it's below 40 PSI, consider adding a booster pump.
- Inspect your pre-filters for discoloration or sediment buildup and replace if needed.
- Listen for water flowing to drain, continuous drainage often indicates a membrane or check valve issue.
- Examine the auto-shutoff valve for debris or damage.
---
#### When to Contact Support
If you've checked the tank pressure, replaced your filters, and verified adequate feed pressure but your tank still isn't filling, it's time to reach out. Our support team can help you determine whether you need a new membrane, replacement valves, or other components. We're here to get your system running smoothly again.
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