Toilet Keeps Running
Updated February 20, 2026
One of the biggest water wasters in a home. Water flows continuously into the bowl or overflows inside the tank. Worn flapper, faulty fill valve, or float set too high. 200+ gallons per day wasted.
Overview
Shows up on the water bill fast. 200+ gallons per day, thousands per month. Always inside the tank, always inexpensive. Three culprits: flapper (rubber seal at the bottom), fill valve (refills the tank), and float (tells the fill valve when to stop). Under 30 minutes, no special skills.
Symptoms
- Still running more than 60 seconds after flushing
- Fill valve cycling on and off without anyone flushing -- phantom flushing
- Constant trickle into the bowl, faint ripple on the water surface
- Tank never fills completely, or fills and immediately starts draining
- Water bill increased with no change in usage
Common Causes
- Worn flapper -- most common cause. Rubber degrades from water and chemical cleaners. Water seeps past into the bowl.
- Faulty fill valve -- internal diaphragm or seal worn out. Will not shut off completely.
- Float too high -- water level rises above the overflow tube, constant stream down the drain.
- Corroded flush valve seat -- minerals or corrosion prevent a seal even with a new flapper.
- Cracked overflow tube -- water drains continuously from tank to bowl.
What You'll Need
How to Fix It
-
Remove the Tank Lid and Observe
Lid off (towel underneath, porcelain chips easily). Flush and watch. Flapper seating properly? Water level rising above the overflow tube? Fill valve shutting off when full? 30 seconds tells you which component.
Tip: Water over the overflow tube? Float or fill valve. Seeping past the flapper into the bowl? Flapper or flush valve seat. -
Check and Replace the Flapper
Water off, flush to drain. Unhook flapper from overflow tube ears, disconnect chain. Warped, stiff, or mineral buildup? Replace. Take old one to match size and style. New flapper on the ears, chain reconnected with half inch of slack.
Warning: Not all flappers are universal. Kohler, American Standard, TOTO often require brand-specific. Check model number (stamped inside the tank) before buying. -
Perform the Dye Test
Food coloring in the tank, 15 minutes, no flushing. Color in the bowl? Flapper seal not holding -- either still bad or flush valve seat needs attention.
Tip: Dye test fails with a new flapper? Flush valve seat has mineral buildup. Fine emery cloth or Scotch-Brite pad. Heavily corroded? Seat repair kit installs over the damaged surface. -
Adjust the Float Level
Water above the overflow tube? Adjust the float. Ball float: bend the arm down or turn the adjustment screw. Integrated float: squeeze the clip, slide down the shaft. Goal: water level 1 inch below the overflow tube. Water on, confirm.
Warning: Too low and the toilet will not flush effectively. One inch below is the target. Many tanks have a water line marked inside. -
Replace the Fill Valve if Necessary
Float adjusted, still running, fill valve old or grinding? Replace it. Water off, flush, sponge remaining water. Disconnect supply line, unscrew locknut underneath. Old valve out, new one in (height: 1 inch above overflow tube). Locknut hand-tight plus quarter turn. Reconnect supply, water on. Fluidmaster 400A or equivalent, 10 minutes.
Tip: Supply line disconnected? End in a bucket, briefly turn on water to flush debris. Sediment clogs new fill valves. -
Verify the Fix
Water on, tank fills. Flush two or three times, listen. Fill valve shuts off, no running water within 60 seconds. Check fill valve base and supply connection for drips. Dry and quiet? Done.
When to Call a Pro
Call a plumber if it still runs after flapper and fill valve replacement, if the flush valve is cracked and needs full replacement, if water leaks from the base or tank-to-bowl bolts, or if it is pressure-assisted or wall-mounted. Running plus water on the floor could mean a failing wax ring or cracked tank.
Prevention Tips
- Flapper every 3-5 years. Rubber deteriorates gradually. Slow leak before it becomes noticeable.
- No drop-in tank tablets with bleach. Accelerates flapper and seal deterioration.
- Check float after any tank repair. Water level 1 inch below the overflow tube.
- Listen for phantom flushing -- early sign of failing flapper before it becomes constant.
- Premium fill valve and flapper kit (Fluidmaster, Korky) for longer service life.