Toilet Making Noise When Not in Use? What It Means
By Emergency Plumb,
A toilet should be silent between flushes. If yours hisses, trickles, refills by itself or bangs when nobody has used it, water is moving where it should not be, and the type of noise tells you which part to look at.
Short answer: A refill every few minutes or hours with nobody flushing means water is leaking from the cistern into the pan, usually past the flush valve seal. A constant hiss or trickle means the fill valve is not shutting off. A hum or vibration during refilling means a worn fill valve washer or high mains pressure. All three are fixed with a part, not a new toilet.
Refilling on its own
Listen for a short burst of refilling at random times. Water is seeping from the cistern into the pan, usually past a perished flush valve seal or a siphon diaphragm, and when the level drops far enough the fill valve opens to top it up.
Test it: add a few drops of food colouring to the cistern and do not flush for half an hour. If colour appears in the bowl, the flush valve is leaking. Replacing its seal, or the whole flush valve on a modern cistern, cures it.
A constant hiss or trickle
Lift the cistern lid. If the water is up at the overflow pipe, or you can see it trickling into the overflow, the fill valve is not closing.
- Float set too high: lower it using the adjustment screw or clip so the valve shuts with the water a little below the overflow.
- Worn washer or diaphragm: the valve closes but not completely. Replace the washer, or the whole valve if it is old.
- Grit in the valve: common after work on the water supply. Turn off the isolating valve, take the valve cap off and flush the grit out.
If water is running down the inside of the pan in a thin sheet rather than into the overflow, it is the flush valve letting by instead.
Humming, whistling or banging
A hum, whistle or vibration while the cistern refills is usually a worn fill valve washer or diaphragm, made worse by high pressure. A bang when the valve shuts off is water hammer: the flow stops suddenly and the pipe jumps. A modern quiet-fill valve usually cures both. If several taps bang too, the pipes may need clipping or the house pressure reducing; see what causes noisy water pipes.
Why it is worth fixing
A toilet that refills or runs between flushes wastes water constantly, and the steady trickle leaves a scale streak down the bowl. Our guides to a running or weak-flushing toilet and yellow stains in a toilet bowl cover both. If you would rather not take the cistern apart, our toilet repair team replaces fill and flush valves at £99 for the first hour and £49 per additional half hour, plus parts.
Questions people ask
Why does my toilet refill on its own every so often?
Water is slowly leaking from the cistern into the pan, usually past a worn flush valve seal. When the level drops far enough the fill valve opens and tops it up, which sounds like a short flush with nobody there. It is sometimes called a ghost flush.
Why does my toilet keep hissing?
A constant hiss means the fill valve is not closing fully, so water keeps entering the cistern and running away through the overflow or into the pan. The float may be set too high, or the valve's washer or diaphragm is worn or has grit in it.
Why does my toilet make a humming or vibrating noise after flushing?
Usually a worn fill valve washer or diaphragm that vibrates as the cistern refills. High mains pressure makes it worse. A modern fill valve, or a pressure-reducing valve for the whole house, quietens it.
Is a noisy toilet wasting water?
If the noise happens without anyone flushing, yes. Water is moving when it should not be, either into the pan or out of the overflow. On a water meter that shows up on the bill.