Why Your Toilet Refills Every 20 Minutes (and the $8 Fix)
A toilet that refills on its own every 20-30 minutes is losing water from the tank into the bowl, which triggers the fill valve. It's not a mysterious plumbing problem — it's usually one rubber part that costs under $10 and takes fifteen minutes to change.
Confirm the diagnosis first
Put a few drops of food colouring in the tank. Don't flush. Wait 20 minutes. If colour appears in the bowl, water is leaking past the flapper. That test costs nothing and it separates a flapper problem from a fill valve problem.
The parts, and what they cost
Nearly all toilets need one of two things: a flapper, or a fill valve. Replace both while you're in there — the parts are cheap and doing them together saves a second disassembly.
| Part | Typical cost | How often replaced |
|---|---|---|
| Flapper | $4–$9 | Every 4–6 years |
| Fill valve | $10–$18 | Every 8–10 years |
| Tank-to-bowl gasket | $6–$12 | Rarely, when the tank is pulled |
Replacing the flapper
Shut off the water at the angle stop behind the toilet. Flush to empty the tank. Sponge out the remaining water. Unhook the flapper from the overflow tube, note how the chain connects, and fit the new one. Turn the water back on and adjust chain slack so there's a little play — too tight holds the flapper open, too loose and the flush is weak.
If it still runs
If the flapper is new and it still refills, the fill valve is likely not shutting off at the right level. Adjust the float height, or replace the valve. If water levels sit above the overflow tube, that's a fill valve adjustment, not a leak.
The mistakes that cost people money
- Replacing the flapper without cleaning the seat it seals against — mineral scale causes the same symptom.
- Buying a flapper without checking the brand/model — some require specific shapes.
- Overtightening the chain so the flush is permanently leaking.
- Ignoring it because 'it's just a little water' — a running toilet can waste hundreds of gallons a day.
Common questions
How much water does a running toilet waste?
A constant small leak can waste several hundred litres a day. A flapper leak cycling every 20 minutes is typically dozens to a few hundred litres daily depending on tank size.
Can I fix it without shutting off the water?
You can, but you'll get a wet floor. Shut the angle stop — it's usually behind the base of the toilet at the wall.