Running constantly: the flapper, almost always
The most common toilet fault there is, and the most expensive to ignore — a running toilet can waste more water than everything else in the house combined.
The flapper is the rubber seal at the bottom of the tank that lifts when you flush and drops back to hold water. Rubber hardens and warps with age, and on our water mineral deposits build up on the seat it lands on. Either stops it sealing, so water trickles into the bowl, the level drops, and the fill valve tops it up — forever.
The test: put a few drops of food colouring in the tank and do not flush. If colour appears in the bowl within 15 minutes, the flapper is leaking. That is the whole diagnosis.
Replacement is a few dollars and requires no tools. Take the old one to the shop rather than guessing — they are not universal. While you are in there, run a finger around the seat it sits on; if it feels gritty, clean it, or the new flapper will fail the same way.
Worth knowing
If the toilet runs only occasionally — a brief refill every few hours with nobody using it — that is the same fault at an earlier stage. It is not haunted and it is not the fill valve; the flapper is seeping slowly.
Weak or partial flush
A flush relies on dumping the tank's full volume quickly. Anything that reduces the volume or slows the dump weakens it.
Start with the water level in the tank. There is a fill line marked on the inside; if the water is sitting well below it, the fill valve is stopping early and the flush has less to work with. That is an adjustment, not a repair.
Next, the chain from the handle to the flapper. Too much slack and the flapper barely lifts before dropping back — a short, feeble flush. Too little and it never seats properly, which produces the running fault above. It wants just enough slack to sit flat with the handle at rest.
If the level and chain are right and the flush is still poor, the likely cause is mineral buildup blocking the rim jets — the small holes under the rim that direct water into the bowl. On our water these scale over. You can clear them with a length of wire and a descaler.
The bowl drains slowly
First, distinguish this from a weak flush — they feel similar. A weak flush moves the water lazily but it clears. A slow drain means water enters the bowl fine but leaves reluctantly.
A partial obstruction in the trap is the usual cause, and a decent flange plunger clears most of them. Use one shaped for a toilet, not the flat cup type meant for sinks — the flat one cannot seal the outlet and mostly moves air.
If plunging does not clear it, a closet auger is the next step and the last one worth doing yourself. Beyond that, stop: forcing anything further risks scratching the porcelain or pushing the obstruction into the branch line where it is harder to reach.
Where it stops being a DIY job
These four mean the problem is outside the tank, and none of them improve with patience.
- Water pooling at the base. Usually the wax seal between toilet and flange has failed. Every flush is now putting a small amount of waste water under the floor. Not urgent within the hour, but genuinely damaging over weeks.
- The toilet rocks. Movement is what destroyed the seal, and re-tightening the bolts against a corroded or broken flange cracks the porcelain. The flange needs inspecting.
- Clogs that keep returning. A properly cleared toilet stays clear. Repeat clogs in one fixture point at the branch line or the vent, not the toilet.
- Sewage smell with everything working. Either a dry trap somewhere or a venting problem. A sewer line is sealed — you should not be able to smell it.
One thing worth checking on every toilet in the house
The shutoff valve behind the toilet. Turn it off and on once a year.
These seize. They sit untouched for a decade, and then on the one day you urgently need to stop water, the handle will not move — or worse, it turns and the valve body weeps because the packing has dried out.
Exercising it annually keeps it working and tells you now, at your convenience, whether it needs replacing. It is thirty seconds per toilet and it is the difference between a contained problem and a wet floor.