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Published by Mo's Plumbing and Heating
Why Does My Toilet Keep Running?
This is the question you ask when it has already been fixed once. A toilet that runs, gets repaired, and then runs again a few weeks later is not telling you the repair was done badly. It is usually telling you that the thing which was replaced was not the thing that was worn.
The Short Answer
Listen to the pattern rather than the noise. A continuous hiss that never stops is the fill valve failing to shut off. A silent trickle you only notice as movement in the pan is the flush valve seal passing. A toilet that is quiet and then refills by itself every twenty minutes or so is the same seal passing more slowly, with the fill valve topping the cistern back up each time the level drops far enough. That third pattern is the one people describe as intermittent, and it is the one most often misdiagnosed.
What the Pattern of the Noise Tells You
Three distinct behaviours, and each points at a different component. This is worth twenty seconds of listening before anything gets opened, because it is the cheapest diagnostic available.
A constant hiss or rush that never stops means water is entering the cistern continuously and leaving through the overflow. The fill valve is not shutting off. On a modern cistern with an internal overflow, that water goes into the pan and you may see nothing at all from outside.
A silent, steady movement in the pan with no filling noise means the flush valve seal is passing and the cistern is not being refilled fast enough to trigger the fill valve. This is the classic slow leak and it can run for months unnoticed, particularly in a bathroom that is used and left quickly.
Refilling in bursts, quiet in between, means the same passing seal but slower. Water leaks from the cistern into the pan until the level drops far enough for the fill valve to open, it tops up, shuts off, and the cycle repeats. People hear the refill and conclude the fill valve is faulty, replace it, and the problem returns, because the fill valve was doing its job correctly the whole time.
Why It Comes Back After a Repair
The commonest version of this question is from someone who has already had it fixed. There are four honest explanations and they are useful to know in order.
The wrong part was replaced, which the burst-refill pattern above causes more than anything else. Replacing a fill valve on a toilet whose seal is passing gives a few days of apparent improvement, because the new valve is crisper about shutting off, and then the underlying leak reasserts itself.
The seat is worn rather than the seal. A flush valve seal lands on a plastic seat, and after enough years that seat can be scored, distorted or roughened. A new seal on a worn seat gives a good result for a few weeks as the fresh rubber conforms, then starts passing again. This is the one that produces two or three repeat visits, and the fix is the whole valve rather than the seal.
Grit keeps returning. If a system carries debris, or if work has been done elsewhere that disturbed the pipework, particles keep arriving at the seal and holding it fractionally open. That presents as intermittent, sometimes fine for a week.
And occasionally the fill valve is fine but is being fed at a pressure it cannot cleanly shut off against, so it chatters or weeps. That one is rarer and usually comes with a noise people describe as a hammer or a shudder rather than a run.
Narrowing It Down Without Buying Anything
Four checks, none of which cost a penny, and between them they will identify which of the above you have.
- Take the lid off and look at the water level against the fill line. Above the line, or spilling into the overflow, means the fill valve. At or below the line means it is not.
- Do the dye test. Colour the cistern water, leave it twenty minutes without flushing, and look in the pan. Colour in the pan is a passing flush valve seal, conclusively.
- Turn the isolator off and mark the water level with a pencil. Come back in an hour. If the level has dropped with the supply off, water is leaving the cistern through the flush valve, and the fill valve is exonerated entirely.
- Lift the flush valve out and look at the seat it lands on, not just the seal. Run a fingertip round it. A groove, a rough patch or a visible score means the seat is the problem and a new seal will not hold for long.
The Repair That Actually Lasts
Where the seat is worn, replacing the whole flush valve rather than its seal is the repair that stops this recurring. It is a larger job because the valve is usually retained by a nut under the cistern, which on a close-coupled suite means separating the cistern from the pan, and that is the point at which many people reasonably hand it over.
Where grit is the cause, the durable fix is cleaning rather than replacing, plus finding out where the debris is coming from. If it started after work elsewhere in the property, it is likely to settle down; if it is persistent, it is worth looking at the supply rather than at the toilet.
And where the fill valve genuinely is at fault, replacing it is straightforward, but set the level properly afterwards. A valve set to shut off too high leaves the cistern permanently near the overflow, which turns a marginal seal into an obvious leak and makes the whole thing look unfixed.
Whatever gets done, run the dye test again a day later. A partial improvement on a slow leak reads exactly like a fix for the first few days, and that is how these get signed off and then come back.
What It Is Costing You While It Runs
Not what people assume, and being straight about it is more useful than exaggerating. A continuously running toilet moves a serious volume of water over a month, but for most Scottish households that does not appear as a bill, so the argument for fixing it is not primarily financial.
What it does cost is real enough. Noise, first, which in a flat with a bathroom off a hall is wearing. Then the risk attached to an external overflow discharging down a wall, which causes staining and, over a winter, freezing and damage. And in a building with neighbours, an overflow that runs into a shared court or down a common gable stops being only your problem.
There is also a wear argument. A fill valve that is opening and closing every twenty minutes, day and night, is doing many times its designed number of cycles, so a slow seal leak eventually costs you the fill valve as well.
The Second Toilet Nobody Listens To
The pattern we see most in this city is not a bathroom toilet running unnoticed. It is the second one. A large share of Glasgow's larger tenement flats and subdivided townhouses gained a second WC at some point, often a small cloakroom off a hall, a converted press, or a shower room added to a back bedroom during a 2000s refit. Those get used a fraction as often, and a slow leak in one can run for a year without anybody being in the room long enough to hear it.
Nothing prompts the discovery either, for the reason set out in the main guide, so the usual sequence is that somebody finally notices the noise while doing something else entirely. If your property has a second toilet, it is worth running the dye test on it once a year purely as a check, and it takes twenty minutes of leaving it alone.
The other local wrinkle is the flat above. In a tenement the first sign of an overflow is often not in the flat with the fault at all: it is a stain appearing on somebody else's ceiling, or a persistent drip in a close. If a neighbour raises that with you, the toilet nobody uses is the first place to look rather than the one you would expect.
Worth adding that soft water helps here. The west of Scotland supply does not scale up components the way harder water does further south, so a fill valve or a flush seal in Glasgow that keeps failing is usually failing for a mechanical reason, a worn seat or persistent grit, rather than furring up. That changes the diagnosis: repeated failure here is a stronger signal that something is worn than the same symptom would be in a hard water area.
When to Call Someone Out
Worth calling once it has been repaired and come back, because that pattern usually means a worn seat rather than a worn seal and the fix is the whole flush valve with the cistern off the pan. Also worth it if you cannot get the cistern lid or the valve out, if the overflow is discharging outside, or if a neighbour has reported damp that might be coming from your overflow. Mo or Kyle do this work, and the useful thing to have ready is which of the three noise patterns you have, because it shortens the diagnosis before anyone arrives.
Toilet Installation in GlasgowCommon Questions
Because the flush valve seal is passing slowly. Water leaks from the cistern into the pan until the level falls far enough for the fill valve to open, it tops up, shuts off, and the cycle repeats. The refill is what you hear. The fill valve is working correctly, which is why replacing it does not fix this.
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Read Next
Full guide
How to Fix a Running Toilet
Water is either passing from the cistern into the pan, which is the flush valve seal, or the cistern is overfilling and spilling into the overflow, which is the fill valve.
How to Fix a Running Toilet With a Button Flush
Take the button out of the lid first, because you cannot get the lid off with it in place on most designs.
Why Won't My Toilet Flush?
Lift the cistern lid and flush.
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