Toilet Keeps Running After Flushing
A running toilet is almost always caused by a faulty flapper, a float set too high, or a worn fill valve. All three parts cost under $15 at any hardware store and replace without special tools. Most fixes take under 30 minutes.
Step-by-Step Fix
- 1
Diagnose the cause
Lift the tank lid. If water is spilling into the overflow tube (the tall tube in the center), the float is set too high. If the water level is below the overflow tube, press down on the flapper — if the running stops, the flapper is the culprit. If neither, the fill valve needs replacing.
- 2
Fix a bad flapper
Turn off the water supply valve behind the toilet. Flush to empty the tank. Unhook the old flapper from the overflow tube ears and disconnect the chain from the flush handle arm. Snap the new flapper in place and reconnect the chain, leaving about half an inch of slack.
- 3
Adjust a high float
On a ball float (a ball on an arm), bend the arm downward slightly or turn the adjustment screw until the water shuts off about an inch below the top of the overflow tube. On a cup float, pinch the clip on the float and slide it down the fill valve shaft.
- 4
Replace the fill valve
Turn off supply water and flush. Sponge out remaining water. Disconnect the supply line under the tank, unscrew the locknut, and pull out the old valve. Drop in the new fill valve, hand-tighten the locknut, reconnect the supply line, and turn water back on. Adjust float height per the new valve's instructions.
- 5
Test
Flush the toilet and watch the tank refill. Water should stop running within 30–60 seconds, with the water level about an inch below the top of the overflow tube. Replace the tank lid.
⚠️ Safety Notes
- Always turn off the supply valve before removing any parts — it's the oval knob behind/below the toilet.
- Have a towel ready — a small amount of water will spill when you disconnect parts.
When to Call a Pro
If you've replaced the flapper and fill valve and the toilet still runs, the flush valve seat may be cracked or corroded. That requires replacing the entire flush valve assembly — a plumber can do it in under an hour.
Not sure which step applies to your situation?
Describe your specific problem to ProAssist and get a tailored diagnosis — free, no sign-up required.
Diagnose My Plumbing Issue →