Order summary
A toilet runs because water is leaving the tank or because the fill valve will not stop. Lift the lid and look: if the tank keeps spilling into the overflow tube, blame the fill valve: it is set high or worn. If not, the flapper or seal is leaking. Fix whichever is the cause.
Numbered steps
- Close the supply valve behind the toilet.
- Flush once, then sponge the last water from the tank.
- Check the flapper: when the rubber feels slimy or has gone stiff or out of shape, replace it with one that matches your flush valve size.
- Check the chain: it should have a little slack, not too much.
- Adjust the fill valve so the water shuts off about 2.5 cm short of the overflow tube's rim.
- Open the supply, let it fill, and watch for a few minutes.
Plumber's tip: Take the old flapper along to the hardware store. Matching it by size and type saves a second trip.
Errors we see on site
- Picking a one-size-fits-all flapper that does not suit the valve.
- Over-tightening tank bolts and cracking the china.
- Leaving the chain too long so it catches under the flapper.
- Forcing a supply valve that will not turn.
When the desk should come out
Call if the supply valve leaks or will not turn, if the tank shows a crack, or once you have swapped parts and it still runs. See toilet repair. If you are planning a renovation, see kitchen sinks and before you finish a basement.
Quick checklist
- Dye test the tank
- Adjust the float height
- Replace a warped flapper
Your questions on this one
Is a running toilet really wasting much?
A lot over a day. It is worth fixing promptly.