Look inside the tank
Lift the tank lid and flush. Watch the chain lift the flapper, the water drain, then the fill valve refill the tank and shut off. Each of those steps can go wrong.
The three common causes
- Flapper leaking. Water slips past a warped or dirty flapper into the bowl. Clean or replace it.
- Fill valve set too high. Water overflows into the overflow tube. Lower the float.
- Chain too short or tangled. It holds the flapper open. Adjust the slack.
Dye test: Add a few drops of food colouring to the tank and wait. Colour in the bowl without flushing means the flapper leaks.
Replacing a flapper
- Close the little valve behind the toilet and flush to drain it.
- Unhook the old flapper and take it to the store.
- Fit the matching new one and reconnect the chain.
- Turn the water back on and test.
When it is more than a flapper
- Water leaking from the tank bolts
- Cracks in the tank
- A fill valve that will not stop
Call for help
If these steps do not fix it, book toilet repair.