Garden 
Affiliate Disclosure
Some links on this page are affiliate links. As an Amazon Associate, we earn from qualifying purchases — at no extra cost to you. We do not buy, test, or physically handle the products we cover; our rankings come from aggregated owner reviews, ratings and expert consensus. Commissions never change our verdicts. How we rank · full disclosure.
To fix a running toilet, open the tank and check four things in order: the flapper (the most common culprit), the chain, the float and water level, and the fill valve. A quick dye test — food coloring in the tank, wait 15 minutes, look for color in the bowl — tells you if the flapper is leaking. Most running toilets are fixed in 10 to 15 minutes with a part costing 5 to 30 dollars, and no plumber. A running toilet can waste around 200 gallons of water a day per the EPA, so it is worth fixing fast.
Everything you need is inside the tank, and the parts are cheap and standardized. We do not test products first-hand; our picks come from aggregated owner reviews and expert consensus, described in how we rank. Here is how to diagnose and fix it.
How a toilet tank works
Understanding the four parts makes diagnosis obvious. When you flush, the flapper lifts and lets tank water rush into the bowl; the tank empties, the flapper drops and seals, and the fill valve refills the tank until the float reaches its set level and shuts the water off.
| Part | Job | Failure symptom |
|---|---|---|
| Flapper | Seals the tank between flushes | Constant or intermittent trickle into bowl |
| Chain | Connects flush lever to flapper | Too tight holds flapper open; too loose won't flush |
| Float | Tells the fill valve when to stop | Set too high, water spills into overflow tube |
| Fill valve | Refills the tank after a flush | Won't shut off, water keeps running |
A running toilet is almost always one of these four failing. Take the tank lid off and set it somewhere safe — it is heavy porcelain.
Diagnose it in five minutes
Two quick tests point you straight to the problem.
- The dye test. Put a few drops of food coloring in the tank and wait 15 to 20 minutes without flushing. If color seeps into the bowl, the flapper is leaking — the most common issue.
- Check the water level. Look at the overflow tube (the open vertical pipe in the middle). If water is at or above its top and spilling in, the float is set too high or the fill valve will not shut off.
- Listen. Intermittent refilling every few minutes ("phantom flushing") is a slow flapper leak. Continuous running with water going down the overflow tube is a fill-valve or float problem.
These three checks isolate the culprit fast. Now fix the part they point to.
Fix 1: The flapper
The flapper is the usual suspect and the easiest fix. Over years the rubber warps, stiffens or collects mineral scale and stops sealing.
- Shut off the water at the supply valve on the wall behind the toilet, then flush to empty the tank.
- Unhook the old flapper from the pegs on the overflow tube and unclip the chain from the flush lever.
- Take it to the store to match the size and style, or buy a universal flapper (a few dollars). Match the brand where you can.
- Install the new flapper onto the pegs, reconnect the chain with a little slack, and turn the water back on.
- Test. Flush and watch it seal; redo the dye test to confirm the leak is gone.
While you are in there, wipe any mineral buildup off the flush-valve seat where the flapper lands — a rough or scaled seat prevents a good seal even with a new flapper.
Fix 2: The chain
A surprising number of running toilets are just a chain problem. If the chain is too long, it can slip under the flapper and hold it open a crack; if too short, it holds the flapper up.
Adjust the chain so there is just a little slack — about a half-inch of play — when the flapper is closed. Move the clip to a different link to lengthen or shorten it, and trim excess chain so a loose end cannot get caught under the flapper. This costs nothing and takes a minute.
Fix 3: The float and water level
If the tank overfills and water runs down the overflow tube, the water level is set too high.
- Set the level about one inch below the top of the overflow tube. Most tanks have a fill line marked inside.
- Float-cup fill valve: pinch the clip on the float cup and slide it down the shaft to lower the level.
- Float-ball (older) valve: gently bend the float arm down, or turn the adjustment screw, to lower where it shuts off.
Recheck after a flush and adjust until the water settles about an inch below the overflow tube.
Fix 4: The fill valve
If the flapper is sealing and the level is set right but the toilet still runs or hisses, the fill valve is worn and not shutting off cleanly. Replacing it is still a DIY job.
- Shut off the water and flush, then sponge out the remaining tank water.
- Disconnect the supply line under the tank and unscrew the locknut holding the old fill valve.
- Lift out the old valve and drop in the new one (about 10 to 20 dollars, adjustable height).
- Reconnect and set the level, turn the water on, and test for a clean shutoff.
A complete repair kit with flapper, fill valve and flush-valve seal runs about 15 to 30 dollars and is the tidy option if the toilet is old and you would rather replace everything at once.
When it is not the tank
Occasionally a running or intermittently refilling toilet points elsewhere. If you have replaced the flapper and fill valve and it still misbehaves, a cracked flush-valve seat or an intermittent leak may need a closer look — see why does my toilet run intermittently. Water pooling at the base rather than inside the tank is a wax-ring or seal issue, not a running-toilet problem.
Fixing a running toilet is one of the best-value repairs in the house: a few dollars in parts against a plumber's 100 to 250 dollar bill, plus real savings on your water bill. For related jobs see how to unclog a toilet without a plunger and how to caulk around a toilet. Everything else is at the bathroom hub.