A toilet that keeps running or refills by itself every so often is wasting water and raising your bill. The fix is usually simple and inexpensive, and most of the time you can do it in under an hour.
Key Takeaways
- The most common cause is a worn or misaligned flapper letting water leak into the bowl.
- A dye test shows whether the flapper is leaking.
- If water runs into the overflow tube, the fill valve or float is set too high.
- Shut off the water supply valve behind the toilet before making repairs.
How a toilet tank works
When you flush, the flapper lifts and water rushes into the bowl. The flapper drops back onto the flush valve seat, and the fill valve refills the tank until the float reaches the set level. Water should stop there. If it keeps running, something in that cycle is off.
Step 1: Look inside the tank
Remove the lid and watch the water after flushing:
- Water spills into the overflow tube: the fill level is too high.
- Water keeps trickling with no overflow: the flapper is probably leaking.
- The flapper does not close completely: the chain may be too short or tangled.
Step 2: The dye test
Add a few drops of food colouring to the tank water. Do not flush. Wait about 15 to 30 minutes. If colour appears in the bowl, the flapper is leaking. Flush afterwards to avoid staining.
Adjusting the chain
The chain should have a little slack, roughly half an inch, when the flapper is closed. Too tight and the flapper cannot seal; too loose and it can get caught under the flapper.
Replacing the flapper
- Turn off the water supply valve behind the toilet.
- Flush to drain the tank.
- Unhook the chain and remove the old flapper from the pegs on the overflow tube.
- Take it to the hardware store to match size and style, or check your toilet model.
- Install the new flapper, attach the chain with a little slack, turn on the water and test.
If the new flapper still leaks, clean the flush valve seat gently with a soft pad to remove mineral buildup.
Adjusting the fill level
The water level should sit about an inch below the top of the overflow tube, or at the mark inside the tank. Depending on the fill valve:
- Float cup: squeeze the clip or turn the adjustment screw to lower the cup.
- Float ball on an arm: bend the arm slightly down or adjust the screw on the valve.
Replacing the fill valve
If adjusting does not stop the water, or the fill valve hisses or refills slowly, replace it. Universal fill valve kits are available at hardware stores and include instructions. You will shut off the water, drain the tank, disconnect the supply line, remove the old valve, install the new one and adjust the height.
Phantom flushes
If the toilet refills briefly every so often without being used, water is slowly leaking from the tank. This is usually the flapper.
When to call a plumber
If the tank itself is cracked, the shutoff valve is stuck or leaking, or water is leaking at the base of the toilet, call a licensed plumber.
Frequently Asked Questions
How much water can a running toilet waste? A significant leak can waste many gallons a day, which shows up on your water bill.
How long does a flapper last? Several years, depending on water quality and cleaning products. In-tank cleaning tablets can wear rubber parts faster.
Do I need special tools? Usually not. A sponge, towel and sometimes adjustable pliers are enough.
The bottom line
Watch the tank, do a dye test and check the chain. Most running toilets are fixed with a new flapper or a fill-level adjustment.
