Quick Answer:
If the tank still refills slowly after you replaced the fill valve, the problem is often upstream: the fill valve may be installed too low or misaligned, the small inlet screen can be clogged, or the shutoff/stop valve feeding the toilet may be partially closed or blocked. Start by confirming the valve’s height and installation, then check the inlet screen and the stop valve before replacing more parts.
Why This Happens
- Fill valve height or orientation: many modern fill valves need their top or float assembly above the overflow tube to allow full flow. If the new valve sits too low or the float is pinned, flow will be limited.
- Inlet screen blockage: a small mesh or plastic screen at the valve inlet or inside the supply coupling catches debris. It easily gets clogged during repairs or from mineral buildup.
- Stop valve restriction: the shutoff valve under the tank can be partially closed, corroded, or filled with sediment. Even if it looks open, it may not be passing full flow.
- Supply-side issues: sediment in the plumbing, a partially closed main, or devices installed on the line can reduce flow. This is why people sometimes see issues after changes like installing a smart shutoff device — check for related restrictions like a clogged filter or reduced port size. For a problem only affecting hot water fill lines, consider the separate hot-side supply as the source of limitation.
Step-by-Step What to Do
1. Confirm fill valve height and basic installation
Turn off the toilet supply and remove the tank lid. Check that the top of the fill valve and its float assembly clear the overflow tube and move freely. If the valve is adjustable, raise it so the float or refill outlet is positioned per the manufacturer’s mark or until it sits above the overflow tube. Make sure the valve stem is straight and the nut under the tank is snug but not over-tightened.
2. Inspect and clean the inlet screen
Shut off the water at the toilet stop valve, flush the toilet to empty the tank, and place a towel or small bucket under the supply connection. Disconnect the supply line at the bottom of the tank or the valve and look for a small screen or washer in the coupling or valve inlet. Rinse the screen under clean water and remove any debris. Replace the washer if worn. Reconnect and test flow.
3. Check the stop valve for partial clogging
With the supply line disconnected, open the stop valve briefly into a bucket so you can see how much water comes through. Low flow at this point means the shutoff or something upstream is the restriction. If the valve is an older multi-turn or a corroded ball-style valve, it may need replacement.
4. Test supply versus valve performance
If the supply flows well into a bucket but the tank fills slowly when the new valve is attached, the valve may be faulty or not adjusted correctly. If the supply is weak into the bucket, the restriction is upstream and replacing the fill valve alone won’t help.
5. Reassemble, flush, and observe
- Reattach the supply line, open the stop valve fully, and let the tank fill while watching the inlet connection and valve operation.
- If the valve has a flush or cleaning setting, briefly cycle it to clear any trapped debris.
- Repeat the flow test if needed after any adjustment or cleaning.
What Not to Do
- Don’t keep replacing fill valves without checking the supply—restriction upstream is common; if uncertain, a plumber is appropriate.
- Don’t force or overtighten plastic valve parts; cracking can cause leaks or misalignment.
- Don’t test flow by leaving electrical devices or finishes exposed to water. Use a bucket and towels to catch water when disconnecting lines.
When to Call a Professional
- If the stop valve is seized, corroded, or you suspect sediment in the in-wall plumbing.
- If multiple fixtures in the house show low pressure, indicating a larger supply problem.
- If you find a damaged supply line, active leaks you can’t stop, or you’re uncomfortable shutting off and disconnecting lines.
Safety Notes
- Always shut off the toilet supply and drain the tank before disconnecting the supply line.
- Use towels and a small container to catch water. Work slowly to avoid sudden spills.
- If you smell gas or find damaged piping, stop and call a professional—don’t attempt repairs beyond basic valve and screen checks.
For related situations, see Slow refill after installing smart shutoff and Slow refill only on hot water side for troubleshooting steps specific to those setups.
Common Homeowner Questions
- Why is the tank still slow after a new fill valve? — Check valve height, inlet screen, and the stop valve; often the restriction is upstream.
- How do I know if the stop valve is the problem? — Disconnect the supply and open the stop into a bucket; low flow means the stop or upstream plumbing is the issue.
- Can I fix a clogged inlet screen myself? — Yes. Shut the water off, remove the supply, rinse or replace the screen, then reassemble and test.
For more related articles, see the nan hub.