How to Stop a Running Toilet

By the Super Simple Digital Tools Team · Updated June 2026 · Easy · 20 minutes

A toilet that runs constantly is usually caused by a worn flapper that won't seal, or a float set too high so water keeps spilling into the overflow tube. Both are quick, tool-light fixes.

Steps

1. Open the tank. Lift off the lid and set it somewhere safe. Watch what happens after a flush to spot the cause.
2. Check the flapper. If the rubber flapper at the bottom looks warped or doesn't seal, turn off the supply, drain the tank, unclip the old flapper and snap in a matching new one.
3. Adjust the float. If water is flowing into the central overflow tube, lower the float so the fill valve shuts off about 2.5 cm below the top of the tube.
4. Inspect the chain. Make sure the lift chain has a little slack — too tight and it holds the flapper open. Adjust the hook to the right link.
5. Test the flush. Turn the water back on, let the tank fill, and flush a few times to confirm it stops running.

Tips

• Add a few drops of food colouring to the tank — if colour appears in the bowl without flushing, the flapper is leaking.
• A whole flapper costs only a few dollars and takes minutes to swap.