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How do you fix a toilet that keeps running?

Updated August 2026

15–30 minutes · Easy DIY

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Nine running toilets out of ten come down to three parts, and you can check all three in 15 to 30 minutes with one pair of pliers: the rubber flapper that seals the tank, the chain that lifts it, and the fill valve that shuts the water off. Start with a dye test, because it tells you which half of the tank to work on. A flapper stuck open moves roughly 200 gallons a day, so this is one of the few repairs that pays for itself inside a single billing cycle. Parts run $5 to $25 at any hardware store.

What you need

Before you start: Close the supply stop under the tank before you pull any part, then open it slowly afterward. Angle stops sit untouched for years, and a stiff one can weep or refuse to reseat once you move it, so know where your main shutoff is first. Wear gloves if you keep bleach tablets in the tank, since the chemistry that eats the flapper is sitting in that water. Never overtighten a plastic nut: a hairline crack in the porcelain turns a $10 repair into a $400 toilet.

Steps

  1. Lift the tank lid off and rest it flat on a towel on the floor. Porcelain lids weigh 10 to 15 pounds and crack the moment they land on an edge.
  2. Run a dye test. Drop food coloring or a dye tablet in the tank, wait 15 minutes without flushing, then look in the bowl. Color in the bowl means water is leaking past the flapper.
  3. Watch one full flush cycle. The tank should refill and go silent with the water line about 1 inch below the top of the overflow tube. Water spilling into that tube means the fill valve is set too high or is not shutting off.
  4. Check the chain. You want about half an inch of slack. Too tight holds the flapper cracked open; too loose lets it slip under the flapper or tangle on the flush lever.
  5. Feel the flapper. Close the supply stop, flush to empty the tank, then rub the sealing edge with a finger. A black smear, warping, or hardened rubber means it is finished.
  6. Unclip the old flapper from the two ears on the overflow tube, take it to the store, and match it. A replacement is $5 to $15. Snap the new one on and reattach the chain with that half inch of slack.
  7. If the tank never overflows but the valve hisses or cycles on its own, adjust the float first. Most fill valves use a thumbscrew or a spring clip on the shaft to set the shutoff level.
  8. Open the supply, let the tank fill, and repeat the dye test. A tank that holds its color for 15 minutes is fixed. Still leaking after a new flapper points at the fill valve, a $12 to $25 part covered on how often to replace a toilet fill valve.

Or hire it out

A plumber charges $125 to $250 to fix a running toilet, and most of that is the minimum service charge rather than the $5 flapper. Two toilets on one visit almost always beats two separate calls.

Done. Now the part everyone skips: doing it again on schedule. Log it in OnOtto and the next reminder for toilet repairs sets itself.

Log this task, get the next reminder

Frequently asked questions

Why does my toilet refill by itself every few minutes?

That is a phantom flush, and a leaking flapper causes it nearly every time. Water seeps from the tank into the bowl until the level drops far enough to trip the fill valve, which tops the tank back up. A slow seep wastes less than a full-time runner but still adds hundreds of gallons a month. Replace the flapper first. If the new one still weeps, run a fingertip around the flush valve seat: a nicked or mineral-crusted seat needs a $10 seat repair kit.

How much water does a running toilet actually waste?

A flapper held fully open can move around 200 gallons a day, which shows up as a $30 to $100 jump on one monthly water bill, more where sewer is metered off water use. The slow seeps are the expensive ones because nobody notices them for months. A dye test twice a year catches both, and it costs nothing. The routine and the timing are on how often to check a toilet for leaks.

I replaced the flapper and it still runs. What now?

Work down the list. Confirm the small refill tube clipped to the overflow is not pushed down inside it, which siphons water continuously. Feel the flush valve seat for scale or a groove. Then watch the fill valve: if it hisses, dribbles, or never quite shuts, swap it for a $12 to $25 universal valve. If the tank sweats or the bowl rocks on the floor, you have a different problem, and the age of the fixture starts to matter. See how long a toilet lasts.

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