Quick Answer:
If you hear constant water but there’s no puddle, the tank is likely leaking into the bowl or over the tank’s overflow tube. Start by listening at the tank: a steady thin flow into the overflow means the fill valve is set too high. If you don’t see overflow but the bowl water is unsettled or slowly rising, the flapper is the usual culprit.
Why This Happens
There are two common hidden paths for a silent leak:
- Water fills past the fill valve’s proper level and spills into the overflow tube. That looks and sounds like a small continuous stream inside the tank.
- The flapper or flush valve seal lets water pass into the bowl between fills. That can move the bowl water slightly or cause the tank to top off periodically.
Other causes include a misrouted refill tube, a cracked internal part, or changes in house water pressure. If the problem started after a recent supply pressure event or work, check the topic Toilet runs after pressure change. If the sound appears only when other water is used in the house, see Toilet runs only when other fixtures used.
Step-by-Step What to Do
1. Listen and look
- Put your ear near the tank and listen. A steady thin flow into the overflow indicates the fill-valve level too high; no overflow but bowl water movement suggests flapper leak.
- Open the tank lid and watch the water line and overflow tube while the sound is happening.
2. Do a dye test
- Turn off the toilet water supply and flush to clear the tank. Add a few drops of food coloring to the tank, wait 10–15 minutes without flushing, and watch the bowl. Colored water in the bowl means water is leaking from tank to bowl.
3. Adjust the fill level
- If water is spilling into the overflow tube, lower the float or adjust the fill-valve per the manufacturer’s simple instructions until the water stops at about an inch below the overflow tube top.
- Replace the fill valve if it keeps drifting or won’t hold the level.
4. Inspect or replace the flapper
- If the dye test shows water in the bowl and there’s no overflow, remove and inspect the flapper for warping, mineral deposits, or damage. Clean the seat and replace the flapper if it doesn’t seal.
5. Check the refill tube and seals
- Make sure the refill tube is clipped above the overflow tube and not inserted too far into it. Check tank-to-bowl gasket and bolts for obvious leaks or damage.
- After any adjustment or part replacement, test by flushing and watching for steady sound or dye movement.
What Not to Do
- Don’t rely on “no visible leak” as reassurance—tank-to-bowl leaks are hidden and won’t show water on the floor.
- If a dye test is positive, a plumber is appropriate rather than ignoring it or doing repeated temporary fixes.
When to Call a Professional
- If the dye test shows water passing into the bowl and simple fixes (flapper or fill-valve) don’t stop it.
- If you can’t identify the source, the tank has a crack, or the toilet runs intermittently despite adjustments.
- When the problem recurs, affects water bills, or you’re not comfortable working on the tank internals.
Safety Notes
- Turn off the toilet shutoff valve before removing parts. If you can’t close it, shut off the house main and drain the tank.
- Avoid using harsh chemical drain products in a tank—these can degrade rubber parts and make sealing worse.
- Do not force plastic fittings; use the correct replacement parts sized for your toilet model.
Common Homeowner Questions
Q: How long can I leave a silent running toilet before fixing it?
A: Don’t wait—hidden leaks waste water and money; fix within days if possible.
Q: Will adjusting the float always stop the noise?
A: If the sound is overflow-related, lowering the fill level often stops it; if the flapper leaks, float changes won’t help.
Q: Is a flapper replacement something I can do myself?
A: Yes—flappers are inexpensive and easy to swap with basic tools, but take the old one to a store or match the model for the right fit.
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