Why the Toilet Keeps Running: Flapper, Fill Valve or Flush Valve
Most running toilets come from one of three cheap parts. A two-minute look inside the tank usually tells you which one is failing and whether you can fix it yourself.
Call (720) 794-0054How a toilet tank works
The tank holds water for the next flush. A flapper at the bottom blocks the opening to the bowl. When you push the handle, a chain lifts the flapper, water rushes out and the bowl flushes. The flapper drops back and the fill valve refills the tank.
A float, either a ball or a cup, tells the fill valve when to stop. An overflow tube catches water if the float fails. Understanding that cycle makes each failure easy to read.
Sort the symptom
Three common failures
| Symptom | Cause | Typical fix |
|---|---|---|
| Tank refills every few minutes without a flush | Flapper leaks into the bowl | Replace the flapper |
| Constant hiss or trickle into the tank | Fill valve is not shutting off | Adjust or replace the fill valve |
| Water runs into the overflow tube | Float set too high or a bad fill valve | Lower the float or replace the valve |
| Handle sticks down | Chain too tight or lever bent | Adjust the chain or the handle |
| Water at the base | Seal problem, not the tank | See the toilet repair page |
Do the dye test
- Do not flushLeave the tank undisturbed.
- Add dyeUse a few drops of food coloring or a dye tablet in the tank.
- Wait fifteen minutesDo not touch the handle.
- Look in the bowlTinted bowl water means the flapper leaks.
- Clean upFlush to clear the dye.
Toilet still running after the fix?
Call and describe what you replaced. The dispatcher will plan the visit.
Fixing the flapper
Close the shutoff valve behind the toilet and flush to drain the tank. Unhook the flapper from its ears and the chain. Take it to a store to match the type, or look for a model number on the tank. Install the new flapper, hook the chain with a little slack and open the valve.
Check the seat at the bottom of the tank. Mineral buildup or a nick can stop a new flapper from sealing. Wipe it with a soft cloth. If it is pitted, the flush valve may need replacing.
Fixing the fill valve
A fill valve that will not shut off often has a worn seal or a stuck float. Try adjusting the float first. Lowering it makes the valve stop sooner. If the hiss continues, replace the valve. Kits are inexpensive and install with a wrench.
Turn off the water, drain the tank, disconnect the supply line and remove the nut under the tank. Install the new valve, reconnect and set the water level one inch below the overflow tube.
When the flush valve is the problem
The flush valve is the assembly under the flapper. If it is cracked or its seat is rough, no flapper will seal. Replacement means removing the tank from the bowl or using a repair kit that fits over the old seat.
If a tank is old, cracked or stained inside, replacement of the whole toilet may cost little more than the repair. See toilet repair and installation for how the choice is made.
What running costs you
A slow leak from the tank to the bowl wastes water without making noise. Over a month, the amount can be large. A bill that rises with no other explanation is a reason to run the dye test in every toilet.
If the toilets pass and the meter still moves, the leak lies elsewhere. A leak detection visit can find it.
Know when to call
- The shutoff valve is stuck or leaks when turned.
- The tank is cracked or the bowl rocks.
- You replaced the parts and the toilet still runs.
- Water leaks at the base or the tank bolts.
- You want a water-efficient replacement.
- Other fixtures show leaks too, as covered on the faucet and sink repair page.
Tools and parts to have on hand
- An adjustable wrench and a small bucket.
- A sponge and towels for the tank water.
- A universal flapper or the one matched to your model.
- A fill valve kit if the hiss does not stop.
- Food coloring for the dye test.
- A new supply line if the old one is stiff or rusted.
Most repairs take under an hour. Replace the supply line while the water is off, since it is the easiest time to do it.
Dual-flush and older two-piece models
Dual-flush toilets use a different flush valve that can leak at the seal. The same dye test works. Some older models use a tank ball instead of a flapper. The principle is the same, but the replacement part differs. If you cannot find parts for an old model, that is a sign to replace the toilet. Newer models use less water per flush and have parts that are easy to buy.
When the toilet runs only sometimes
An intermittent run is harder to catch than a constant one. The toilet may refill by itself every ten or twenty minutes, or only at night when the house is quiet. That pattern points to a slow leak past the flapper.
Try the dye test once in the evening and again in the morning. A flapper can seal when it is fresh and slip when the rubber is cool or warm. Also lift the chain and watch it. A chain that catches on the lever arm can hold the flapper open for a moment after each flush.
If both tests pass and the tank still refills, look at the fill valve. A float that sits a little high can send water into the overflow tube, which looks like a hiss. Lower the float one notch and watch the water level. If the problem continues after the parts are replaced, the leak may sit at the base or in the supply line. The toilet repair and installation page lists those cases.
Prevent repeat trouble
- Replace flappers every few years, since rubber degrades.
- Avoid in-tank bleach tablets, which damage rubber parts.
- Clean mineral buildup at the flapper seat.
- Keep the chain slack but not tangled.
- Test the shutoff valve once a year.
Hard water speeds up wear. A softener helps, and the water softener page explains how.
Quick answers
Add dye to the tank. If color reaches the bowl without flushing, it leaks.
Water slips past the flapper and the fill valve tops off the tank.
Often several years, less in hard water or with bleach tablets.
Many homeowners do. Kits fit most toilets.
When the tank is cracked, parts are obsolete or repairs keep failing.
Stop the leak you cannot hear
Call to repair or replace a toilet and fix the cause.