Do this now
Take the cistern lid off and put it flat on the floor, not balanced on the seat. It is heavy porcelain and it cracks. Everything you need to see is inside.
Toilet will not flush: take the lid off, it is almost always in there
Updated
A toilet that will not flush divides cleanly. The handle feels loose and nothing moves, which is the chain or the lift arm. The flush is weak and incomplete, which is the water level or a flapper closing too early. Or the cistern is not refilling at all, which is the fill valve or the supply. All three are visible from above and all three are cheap parts.
- 01
Watch a flush from above
Lid off, then flush and look. The lever should lift the chain, the flapper should swing open and stay open until most of the water is gone. Watching this once tells you more than any amount of description.
- 02
Check the chain slack
Too much slack and the lever pulls through without lifting the flapper. Too little and the flapper never seats, which is the running toilet problem instead. Half an inch of slack is about right, adjusted by moving the clip a link or two.
- 03
Look at the water level
It should sit about an inch below the top of the overflow tube. Low water is a weak flush, because the flush is driven by the weight of water above the flapper. Adjust the float: a screw on modern fill valves, a clip on the rod on older ball ones.
- 04
Inspect the flapper itself
Run a finger around the rubber. If it is hard, warped or leaves black on your finger, it has perished and is not sealing or not staying open. It is a few dollars, takes five minutes and needs no tools.
- 05
Confirm the supply is on
The shutoff valve behind the toilet, fully open. If the cistern refills very slowly, the fill valve may be blocked with grit, which is common after any work on the water supply anywhere in the house.
- 06
If the cistern is fine, suspect the bowl
Full cistern, good flapper, correct level, and still a weak flush points at the rim jets or the siphon jet in the bowl being blocked with mineral scale. A mirror and a bent wire will show you the rim holes under the lip.
What it costs
| Cost | Source | |
|---|---|---|
| Flapper | about $5 to $15 | |
| Fill valve | about $12 to $25 | |
| Toilet repair | $100 to $300 | |
| Plumber minimum call-out | $50 to $150 |
Every figure here is published by the source named beside it. We do not average them into a number of our own.
Where to stop
Almost all of this is homeowner work, so the list is short and mostly about knowing when the toilet is not the problem.
- Other drains gurgling or backing up
- The blockage is in the main line, not the toilet, and nothing inside the cistern will change it.
- Water at the base of the toilet
- That is the wax seal rather than the flush, and it means water is getting into the floor.
- A cracked cistern or bowl
- Porcelain is not repairable. A hairline crack becomes a split, and a split cistern empties its contents onto the floor.
- Repeatedly weak flushing on a low-flow toilet with a long drain run
- That can be a design mismatch rather than a fault, and it is worth a proper diagnosis rather than a third flapper.
Why it happened
Everything inside a cistern is rubber and plastic sitting in water permanently, and rubber perishes. A flapper has a working life of a few years, chains stretch, and the mineral in the water slowly coats the rim jets. None of it fails suddenly. The flush has usually been getting weaker for a year before somebody calls it broken.
What stops it happening again
Take the lid off twice a year and look. A flapper that leaves black on your finger is on the way out, and replacing it before it fails costs the same as replacing it after. Drop-in cistern tablets are worth avoiding: the bleach in them destroys exactly the rubber parts this guide is about.
- The part
- A flapper, a few dollars, kept in the cupboard. It is the single most replaced part in any bathroom.
- How often
- Look inside the cistern twice a year. Replace the flapper when it hardens rather than when it fails. No bleach tablets in the tank.
Want the rest of the house covered?
One email a month, timed to the systems you actually have. The same kind of thing as the tablet: small, cheap, and it stops the call.
Also asked
- The handle is loose and nothing happens. What is wrong?
- The chain has come off the lever arm or has too much slack, so the handle moves without lifting the flapper. Take the lid off and look: it is visible immediately and free to fix.
- Why is my flush weak?
- Usually the water level is too low, or the flapper is closing before the cistern has emptied. The level should sit about an inch below the top of the overflow tube.
- Should I use drop-in cistern cleaning tablets?
- No. The bleach in them attacks the rubber flapper and seals, so they cause exactly the failure they seem to prevent.
- The cistern fills very slowly. Why?
- A partly closed shutoff valve or grit in the fill valve, which is common after any plumbing work elsewhere in the house. Both are cheap to sort.
- Everything in the tank looks fine and it still flushes weakly.
- Look at the rim jets under the lip of the bowl and the siphon jet at the bottom. Mineral scale blocks them gradually, and a mirror plus a bent wire will show you.