Toilet runs only when house is quiet

Quick Answer:

If you only notice the running when the house is quiet, it’s usually a slow or intermittent leak inside the toilet tank (flapper, fill valve, or overflow). A simple isolation test will confirm it: close the toilet stop valve for an hour; if the running noise stops, the problem is inside the toilet. Reopen the valve and watch the refill behavior to see how and when water is entering the bowl.

Why This Happens

Many toilet sounds are low-volume and easy to miss when appliances and people are making noise. Common internal causes include:

• a worn or missealed flapper letting water slowly leak into the bowl;
• a fill valve that drifts and allows small amounts of water to flow until the tank reaches its set level;
• a cracked or misaligned overflow tube or an incorrect water level that lets water spill into the overflow;
• an intermittent issue that only shows between flushes, so you hear it only when the house is quiet.

If you see the toilet run for longer than expected after a flush, it points toward the fill valve or float adjustment. In other situations, a slow leak from the tank to the bowl is most likely responsible for faint, persistent sounds.

Step-by-Step What to Do

1. Confirm by isolating the toilet

Locate the shutoff (stop) valve at the base of the toilet and turn it clockwise to close it. Wait for about an hour while the house is quiet. If the running noise disappears during that time, the issue is coming from the toilet tank or its internals.

2. Reopen and observe refill behavior

Slowly turn the stop valve back on, then flush the toilet and watch what happens:

• Note whether water continues to run after the tank should be full.
• Watch the fill valve and the water level in the tank; see if the fill valve reopens or trickles water back into the tank or bowl.
• If the sound returns right away or only when the water is turned back on, that can indicate a fill-valve or pressure-related response—refer to Toilet runs after turning water back on for more on that scenario.

3. Do a dye test

With the tank full, add a few drops of food coloring to the tank, wait 10–15 minutes without flushing, and see if colored water appears in the bowl. Color in the bowl = a leak past the flapper or another tank-to-bowl leak.

4. Inspect and adjust common parts

Look for these simple fixes:

• Check the flapper for warping, mineral buildup, or a damaged seal; replace if it doesn’t seat well.
• Adjust or replace the fill valve or float if the tank overfills or the valve lets water trickle.
• Ensure the overflow tube isn’t cracked and that the water line is set below its top.
• Confirm the flapper chain has a little slack but not so much that it prevents a full seal.

5. Monitor and retest

After any adjustment or part replacement, repeat the isolation test and the dye test to confirm the sound is gone. If the toilet still produces faint noise only in quiet moments, replace the suspect component or move to the next troubleshooting step.

What Not to Do

• Don’t keep the stop valve half-closed long-term to quiet a running toilet—fix the cause; if you can’t, a plumber is appropriate.
• Don’t continuously ignore a running toilet; even small leaks waste water and can raise your bill.
• Don’t use harsh chemicals in the tank to “fix” a leak; they can damage parts and make the problem worse.

When to Call a Professional

Call a plumber if any of the following apply:

• You can’t identify the source after the isolation and dye tests.
• Replacing a flapper or fill valve does not stop the running.
• Multiple fixtures are making similar noises, suggesting a supply pressure or pipe issue.
• The toilet is old or the internal parts are hard to access or corroded.
• The issue involves the supply line or valve you’re uncomfortable working on—getting professional help avoids accidental flooding or damage.

When the toilet goes into a long refill cycle or won’t shut off after adjustments, consider the explanation in Toilet runs longer than normal as a guide for the plumber or for the next troubleshooting step.

Safety Notes

• Turn off the water supply at the stop valve before removing tank parts to avoid spills.
• Use basic hand tools and avoid excessive force—overtightening plastic fittings can crack them.
• If you smell gas, hear hissing from supply lines, or see corrosion that looks unsafe, stop and call a professional.
• Don’t attempt soldering or major pipe work unless you have proper training and tools.

Common Homeowner Questions

• Q: How long does the isolation test need to be?
  A: An hour is usually enough to hear a persistent trickle; for very slow leaks, check again after a few hours.
• Q: Will replacing the flapper usually fix this sound?
  A: Often yes—flappers are inexpensive and a common cause of quiet, continuous running.
• Q: Could high water pressure cause the problem?
  A: Yes, unusually high supply pressure can make fill valves behave oddly; a plumber can test and address pressure issues.