Technically reviewed by the Master Plumbing Team at a licensed residential plumbing service for accuracy and safety.
A running toilet is when water continues flowing from the tank into the bowl after a flush. In most homes, the cause is one of three issues: a worn flapper, a mispositioned fill tube, or a water level set too high.
This is not a small problem. According to the EPA WaterSense program, a running toilet can waste 200 gallons of water per day or more. Depending on local water rates, that can add $30 to $70 per month to your water bill, quietly and continuously.
The good news is that most running toilets can be fixed in under 15 minutes with basic tools.
What You Need Before You Start
- Screwdriver
- Adjustable pliers
- Replacement flapper (most are universal, but Korky and Fluidmaster are industry standards for durability)
- Wooden spoon or similar tool for testing
- Replacement fill tube if damaged
Safety note: Turn off the water supply valve behind the toilet before working inside the tank. Hand-tighten valves only. Using tools on old plastic fittings can cause cracks and leaks.
Step 1: Test and Replace the Flapper
The flapper is the rubber seal at the bottom of the tank. When it hardens, warps, or builds up mineral deposits, it no longer seals fully. Water leaks into the bowl, forcing the fill valve to run repeatedly.
The Pressure Test (Professional Diagnostic)
Remove the tank lid and flush the toilet. Once the flapper closes, apply even downward pressure on it using a wooden spoon or similar tool.
- If the running stops immediately, the flapper is the failure point.
Replace the Flapper Correctly
- Shut off the water supply valve.
- Flush to empty the tank.
- Unhook the chain from the flush lever.
- Remove the old flapper from the overflow tube pegs.
- Install the new flapper, matching the mounting style.
- Adjust the chain to leave about ½ inch of slack.
Watch out:
Many new flappers come with a thin plastic protective film on the sealing surface. Remove it completely. Leaving this film on is one of the most common reasons a “new” flapper still leaks.
Turn the water back on and let the tank refill. If it fills once and stops silently, move on only if the problem persists.
Step 2: Inspect and Correct the Fill Tube
The fill tube is the small hose that sends water from the fill valve into the overflow pipe to refill the bowl after flushing.
If this tube is pushed too far down into the overflow pipe, it creates a siphon that causes constant refilling.
What to Check
- The fill tube should sit above the overflow pipe opening.
- It should never be submerged in water.
What to Do
- Clip the tube to the side of the overflow pipe.
- Trim excess length if necessary.
- Replace the tube if it is cracked or brittle.
Flush once and confirm the bowl refills normally without triggering continuous tank filling.
Step 3: Adjust the Water Level (Float Height)
If the water level is too high, excess water flows into the overflow tube, keeping the fill valve running.
The correct level is 1 to 1.5 inches below the top of the overflow tube.
Identify Your Valve Type
- Fluidmaster-style vertical float valve (cup-style):
Pinch the adjustment clip or use the adjustment screw to lower the float. - Ball float valve (older American Standard or Kohler models):
Gently bend the metal arm downward or turn the adjustment screw if present.
Flush the toilet two to three times. The tank should refill to the same level and shut off completely each time.
When to Stop and Call a Professional
DIY fixes are effective, but knowing when to stop is part of real expertise. If you find yourself facing complex issues beyond these three steps—such as persistent sewage smells or a cracked main line—it’s time to seek expert help. For those needing specialized residential support, professional Taiwan plumbing services can provide the localized expertise and equipment necessary for high-density housing systems.
Stop immediately and call a plumber if:
- You see a hairline crack in the porcelain tank (risk of sudden flooding).
- The shut-off valve behind the toilet is leaking, seized, or will not close (main-line issue).
- You hear a thumping or banging sound when the toilet stops filling (water hammer risk).
Ignoring these signs can turn a small repair into major water damage.
Final Takeaway
Most running toilets are not plumbing failures. They are maintenance issues caused by worn or misadjusted parts.
With a properly installed flapper, a correctly positioned fill tube, and an accurately set water level, you can eliminate nearly 90 percent of running toilet problems yourself. Fixing it early saves water, lowers your bill, and prevents bigger repairs down the line.
