Quick Answer:
If the hammering happens right at the end of the refill, slow the refill by closing the angle stop slightly and feel the supply line and shutoff for vibration. If that doesn’t help, or if the angle stop or supply line is seized or corroded, call a plumber to check pressure and secure or replace worn parts.
Why This Happens
Most post-replacement hammering is a water-hammer or vibration issue that appears when the fill valve (or angle stop) closes quickly. A new valve can close faster or travel differently than the old one, which can create a brief pressure spike or a sudden shutoff shock. If pipes or the flexible supply line are loose, that shock becomes a hammer noise as pipe hits framing or a fitting vibrates.
Listen to when the sound occurs. If it’s at the end of the refill, it’s usually a valve/pressure or support issue. If you find the noise in other places or only when certain taps run, see Pipes bang when toilet shuts off or Banging only on hot water for related troubleshooting ideas.
Step-by-Step What to Do
1. Confirm timing of the hammer
- Flush and watch/listen closely. Note whether the noise happens while the tank is filling or right after the fill valve closes.
- If the knock is at the exact moment the water stops, you’re dealing with end-of-refill shutoff action—not a continuous vibration during filling.
2. Slow the refill from the angle stop
- Locate the angle stop (the shutoff on the toilet supply line). Turn it clockwise a quarter turn or less to restrict flow slightly.
- Flush and observe. Slowing the refill often reduces the pressure spike and stops the hammering.
- If the noise stops, leave the stop partly closed so the valve closes more gently, then adjust for a balance between refill speed and silence.
3. Feel the supply line and shutoff for vibration
- Put your hand on the shutoff and the flexible supply line as the tank finishes refilling. If you feel a sudden thump or strong vibration at that moment, the noise is traveling through the line or fitting.
- Check if the nut at the fill valve or the supply nut is loose. Don’t tighten excessively—see the What Not to Do section.
4. Compare with another toilet or fixture
- Flush a different toilet, preferably on the same floor or the same branch of plumbing. If that toilet has the same hammer, the problem may be system-wide (pressure or support). If it’s quiet, the issue is likely isolated to the replaced valve, the supply line, or the local support.
5. Inspect visible fittings and pipe support
- Look for a loose or unsupported pipe where it runs into the wall or floor. If pipes move and hit framing during the shutoff, adding clamps or supports will stop the noise. A plumber can secure hidden runs.
- Check the flexible supply line for kinks or corrosion. If it’s compromised, replacement is better than trying to force a solution.
What Not to Do
- Don’t overtighten the supply nut. Over-torquing can crack plastic fill valves or damage threads.
- Don’t twist or turn the fill valve body to chase the noise. Twisting can stress internal parts and cause leaks.
- If the angle stop is seized or the supply line shows corrosion, don’t force it. Have a plumber replace the valve or line rather than risking a break or a leak by forcing removal.
When to Call a Professional
Call a plumber if any of these are true:
- Slowing the refill does not stop the hammering.
- The angle stop or supply line is seized, corroded, or leaking.
- The same hammer happens at multiple fixtures (possible high pressure or a water hammer arrestor issue) or pipes inside walls need securing.
- You are unsure how to shut off the main water, or you are uncomfortable working on the supply fittings.
A plumber can measure water pressure, add or replace arrestors, replace corroded parts, and secure hidden pipe runs safely.
Safety Notes
- Turn the shutoff fully off before disconnecting the supply line. If unsure, turn off the house main.
- Have a small bucket and towel ready to catch water when loosening fittings.
- Avoid forcing seized valves—forcing can cause sudden failure and a large leak.
- If you smell gas (unlikely from toilet work) or see major corrosion, stop and call a professional immediately.
Common Homeowner Questions
- Is the new fill valve defective? Not necessarily; often the noise is from faster shutoff, pressure spikes, or loose pipes.
- Will a washer or extra nut stop the noise? Probably not—adding hardware won’t fix pressure spikes or loose pipe support; proper adjustment or professional repair is better.
- Can I live with the noise? It’s usually not dangerous, but it can signal stress on fittings and pipes; have it checked if it continues or is loud.
For more related articles, see the Pipes Banging After Fixtures Turn Off hub.