How to fix a running toilet

A toilet that keeps running wastes water and makes a steady hiss or trickle that is hard to ignore. The cause is almost always one of a few cheap parts inside the tank, and swapping them is a job most people can do in under an hour with no special tools. Lift the tank lid, set it somewhere safe, and watch what happens after a flush.

How a toilet tank works

When you press the handle, a chain lifts the flapper, a rubber seal at the bottom of the tank, and the water rushes into the bowl. As the tank empties, the flapper drops back and seals the opening. The fill valve then refills the tank, and a float rises with the water until it reaches its set height and shuts the valve off. The overflow tube, a vertical pipe in the middle, carries away any water that rises too high so the tank cannot overflow.

A toilet runs when that cycle never settles. Either water keeps leaking past the flapper, so the fill valve keeps topping up, or the level is set so high that it spills into the overflow tube and the valve never shuts. Almost every running toilet traces back to one of those two faults.

• A faint trickle into the bowl between flushes points to a leaking flapper.
• Water running into the overflow tube points to a level set too high.
• A hiss that comes and goes on its own points to a worn fill valve.
• Running only right after a flush usually means the chain is catching.

What you need

Run the dye test

The dye test tells you whether the flapper is leaking, the most common cause. With the tank refilled, add a few drops of food colouring and stir gently. Do not flush. Leave it about fifteen minutes, then look in the bowl. If colour has appeared, water is seeping past the flapper and it needs replacing. If the bowl stays clear, the flapper is sealing and the problem is the water level or the fill valve instead.

Replace a worn flapper

Flappers are rubber, and over a few years they harden, warp, or grow a film that stops them sealing. Take the old one to the shop or note the brand of your toilet, since flappers come in a few sizes and the fit matters.

1. 1

   Remove the old flapper

   With the supply off and the tank empty, unhook the chain from the handle arm and slide the flapper ears off the pegs on each side of the flush valve.

2. 2

   Fit the new flapper

   Wipe the valve seat so no grit stops it sealing, then clip the new flapper onto the same pegs so it sits flat over the opening.

3. 3

   Set the chain length

   Reconnect the chain to the handle arm with a little slack. Too tight and the flapper cannot close; too loose and it can slip under the flapper and hold it open.

4. 4

   Turn the water back on and test

   Open the supply valve, let the tank fill, and flush once. Watch the flapper lift cleanly and drop to a full seal.

Adjust the float and water level

If the dye test came back clear, look at the water level against the overflow tube. It should sit about an inch below the top. If water is spilling in, the float is too high and the fill valve never shuts, so lowering the float lowers the level. On a newer column style valve, pinch the clip and slide the float cup down, or turn the screw on top; on an older ball float, bend the arm gently downward. Make a small change, let the tank refill, and check again.

Adjust or replace the fill valve

If the level is correct and the flapper is new but the toilet still hisses or cycles on its own, the fill valve is likely worn. Many have a cap you can lift and rinse to clear grit, worth trying first. If that does not help, replacing the whole valve is still a beginner job: shut off the supply, flush, sponge out the water, undo the lock nut under the tank, lift the old valve out, and fit the new one to the marked height.

Working through the parts in this order fixes most running toilets. If the tank still will not settle, or water leaks onto the floor rather than inside it, that points to a worn tank bolt or gasket and is a sensible time to bring in a plumber.