Why Does My Toilet Keep Running? Causes and Fixes
Your toilet keeps running most often because the rubber flapper no longer seals, letting water leak from the tank into the bowl so the fill valve runs to keep up. A tangled flapper chain, a misadjusted float, or a worn fill valve are the other common causes, and all are inexpensive DIY fixes.
By Lara Holm
·Staff Writer ·
·
5 min read
Your toilet keeps running most often because the rubber flapper at the bottom of the tank no longer seals, letting water leak into the bowl so the fill valve keeps running to top it up. A tangled flapper chain, a misadjusted float, or a worn fill valve are the other usual causes. The good news is that these are inexpensive, do-it-yourself fixes that rarely need a plumber.
Why does my toilet keep running?
A running toilet means water is constantly moving from the tank into the bowl, so the fill valve runs to replace it. The leak almost always comes from one of three places: a flapper that is not sealing, a water level set too high so water spills down the overflow tube, or a fill valve that will not shut off. Lifting the tank lid and watching how the parts behave tells you which one you have in under a minute.
Is it the flapper?
A leaky flapper is the single most common cause. The flapper is the rubber seal that lifts when you flush and drops back to hold water in the tank. Over time it warps, stiffens, or wears out and stops sealing, so water seeps into the bowl and the fill valve keeps running.
- Remove the tank lid and watch the flapper after a flush; if it does not drop and seal flat, it is suspect.
- Check the water level. If it stays below the overflow tube, a leaking flapper is the likely cause.
- Press down gently on the flapper; if the running stops, the flapper needs replacing.
How do I check the chain and float?
Sometimes the flapper is fine but something stops it from seating.
- Inspect the chain. A chain that is kinked, snagged on the flush lever, or too short holds the flapper open slightly. Adjust it so there is a little slack but no tangle.
- Check the float. If water rises above the overflow tube, the float is set too high. On modern valves, turn the adjustment knob or screw above the float cup to lower the water level to about an inch below the top of the overflow tube.
How do I replace a worn flapper?
Replacing a flapper is one of the easiest home repairs.
- Turn off the water supply valve behind the toilet and flush to empty the tank.
- Unhook the old flapper from the pegs on the overflow tube and detach the chain.
- Take the old flapper to the store to match the size, or buy a universal flapper.
- Attach the new flapper, reconnect the chain with a little slack, turn the water back on, and test.
Why is my toilet still running after a new flapper?
If a new flapper does not fix it, the flush valve seat, the ring the flapper rests on, may have mineral or calcium buildup that prevents a seal. Turn off the water, drain the tank, and gently clean the seat with a sponge or fine scouring pad. If the seat is cracked or pitted, that part may need replacing. If the water level still rises above the overflow tube, the fill valve itself is the problem.
How do I fix or replace the fill valve?
When water keeps pouring down the overflow tube no matter how you adjust the float, the fill valve is worn and should be replaced. Fill valves are sold as complete kits and swap out in about 20 minutes.
- Shut off the water, flush, and sponge out the remaining water.
- Disconnect the supply line and unscrew the locknut under the tank to remove the old valve.
- Install the new valve per the kit instructions, set the height, and reconnect the supply line.
- Turn the water on, let the tank fill, and adjust the water level to the mark inside the tank.
Running toilet: diagnose at a glance
| What you see | Likely cause | Fix |
|---|---|---|
| Water level below overflow tube | Flapper not sealing | Clean seat or replace flapper |
| Water spilling into overflow tube | Float set too high | Lower float, or replace fill valve |
| Flapper held slightly open | Tangled or short chain | Adjust chain slack |
| Still runs after new flapper | Buildup on valve seat | Clean or replace the seat |
| Fill valve never shuts off | Worn fill valve | Replace the fill valve |
When should I call a plumber?
Most running toilets are solved by cleaning the seat and replacing the flapper or fill valve, all low-cost parts. Call a licensed plumber if the toilet still runs after you have replaced those parts, if you find a crack in the tank or bowl, or if there is water leaking onto the floor rather than into the bowl. A continuously running toilet wastes water and raises your bill, so it is worth fixing promptly.
Frequently asked questions
What is the most common cause of a running toilet?
A worn or poorly seated flapper is the most common cause. As it fails to seal, water leaks from the tank into the bowl, and the fill valve keeps running to replace it.
How do I know if it is the flapper or the fill valve?
Check the water level. If it stays below the overflow tube, the flapper is likely leaking. If water rises above the overflow tube and spills in, the fill valve or float needs adjusting or replacing.
Why does my toilet still run after replacing the flapper?
The flush valve seat may have mineral buildup preventing a seal, the chain may be too tight, or the fill valve may be the real problem. Clean the seat and check the chain and fill valve.
Can a toilet chain cause running water?
Yes. A chain that is kinked, snagged on the lever, or too short holds the flapper open slightly. Adjust it so it has a little slack and lets the flapper seat fully.
Is a running toilet wasting a lot of water?
Yes, a continuously running toilet can waste a significant amount of water over time, which raises your water bill. Fixing it promptly is worthwhile.
When should I call a plumber for a running toilet?
Most running toilets are easy DIY fixes. Call a licensed plumber if replacing the flapper, fill valve, and cleaning the seat does not stop it, or if there is a crack or leak outside the tank.
