How to Fix a Running Toilet

A running toilet is one of the most common and fixable household problems. It wastes hundreds of gallons of water per week and can add $50–$100 to your water bill. The good news: it's almost always a cheap fix you can do yourself.

Step 1: Diagnose the Problem

Take the lid off the back of the toilet (the tank) and set it aside safely. Look inside while the toilet is running. There are two main culprits:

The flapper — a rubber seal at the bottom of the tank that opens when you flush and seals shut after. If water is constantly trickling into the bowl, a worn flapper is usually the cause.

The fill valve / float — controls how high the water fills in the tank. If water is running into the overflow tube (the tall pipe in the center), the water level is too high.

Quick test: Put a few drops of food colouring in the tank. Wait 15 minutes without flushing. If colour appears in the bowl, your flapper is leaking.

Fix 1: Replace the Flapper (Most Common Fix)

Flappers wear out after 3–5 years. A universal toilet flapper costs $5–$10.

1. Turn off the water supply — the shut-off valve is on the wall behind the toilet base. Turn it clockwise.
2. Flush the toilet to empty the tank.
3. Unhook the old flapper — it clips or slides off the two pegs on either side of the flush valve.
4. Take the old flapper to the hardware store to match the size, or buy a universal flapper.
5. Attach the new flapper to the pegs and hook the chain to the flush handle arm (leave a little slack — about ½ inch).
6. Turn the water back on, let the tank fill, and test.

Fix 2: Adjust the Float

If water is running into the overflow tube, the float (which tells the fill valve when to stop) is set too high.

Ball float (older toilets — a ball on an arm): Bend the float arm down slightly, or turn the adjustment screw if there is one.

Cup float (newer toilets — slides up and down the fill valve): Pinch the clip and slide it down, or turn the adjustment screw counterclockwise.

The water level should be about 1 inch below the top of the overflow tube. Adjust, let it fill, and check.

Fix 3: Replace the Fill Valve

If adjusting the float doesn't help, the fill valve itself may be worn and constantly leaking. A replacement fill valve costs $10–$15 and takes about 20 minutes to install.

1. Shut off the water and flush to empty the tank
2. Disconnect the water supply line from the bottom of the tank
3. Unscrew the locknut holding the fill valve and lift it out
4. Install the new fill valve (they come with instructions), set the height according to your tank
5. Reconnect the supply line and turn the water back on

When to Call a Plumber

If you've replaced both the flapper and fill valve and the toilet is still running, there may be a crack in the flush valve seat (the part the flapper seals against) — this usually requires replacing the whole flush valve or the toilet internals, which is a more involved job but still DIY-possible with a toilet repair kit.

If you're uncomfortable with any of this, a plumber will typically charge $75–$150 to fix a running toilet — still much cheaper than ignoring it.