The two-minute test
Put a few drops of food colouring in the cistern. Do not flush. Come back in fifteen minutes and look in the bowl. Colour in the bowl means the outlet valve is leaking. No colour means the inlet valve is the problem.
Either way, it is a small part. Call R&G on 0461 330 531—$ 0 call-out fee.
If your toilet keeps running with nobody near it, one of two valves is failing to seal, and a few drops of food colouring will tell you which one in fifteen minutes.
Nothing here is urgent, and nothing here is expensive. It is just quietly costing you money every hour until someone fixes it.
There Are Only Two Valves
Lift the cistern lid off and look in. However complicated it appears, a toilet does two things,s and each has one valve.
The inlet valve lets water in and is supposed to shut off when the cistern reaches its fill line. The outlet valve sits in the floor of the cistern and holds that water there until you press the button.
If the outlet valve stops sealing, water trickles continuously into the bowl. The level drops, the inlet valve notices and tops it up, and you get a refill every so often with nobody near it. That is the phantom flush.
If the inlet valve stops shutting off, water keeps arriving, the level rises past the overflow tube, and it pours down that tube into the bowl. You get a constant trickle rather than a cycle.
Everything else on this page is working o, so which of those two do you have?
What the Dye Test Tells You
Food colouring from the kitchen, a dozen drops into the cistern water, lid back on, and leave it alone for fifteen minutes. Do not flush.
| What you find | What it means |
|---|---|
| Coloured water in the bowl | The outlet valve seal is passing. The most common fault by a distance |
| Bowl still clear, but water running | The inlet valve is not shutting off, and water is going over the overflow |
| Water level sitting right at the top of the overflow tube | The fill level is set too high, or the inlet valve has drifted. Sometimes just an adjustment |
| Nothing moves, and the noise has stopped | An intermittent fault, usually grit under the outlet seal. It will come back. |
The useful version for us on the phone is the “but”. It runs, but nobody has flushed it. Or it runs constantly, but the bowl water stays clear. Either sentence tells us which part to bring.
One thing this is not. If water rises in the bowl when you flush rather than draining away, that is a blockage and a completely different problem, covered in why the water rises when you flush.
What Is Actually Worn
Four candidates, and three of them are a small rubber part.
- The outlet valve seal. A rubber washer or diaphragm that sits on a plastic seat. It hardens, distorts or collects grit, and once it stops sitting flat,t it never seals again. On a cistern that has never been serviced, this seal is as old as the toilet.
- The outlet valve seat. The surface the seal sits on. If it has scaled or scored, a new seal on an old seat will leak again within months, which is why a cheap part-swap sometimes does not hold
- The inlet valve. Also called the fill or float valve. It wears, it sticks, and it drifts out of adjustment, so it either will not shut off or shuts off at the wrong level. The same part failing the other way is what causes a cistern that fills too slowly.
- The cistern itself. Occasionally the fault is a hairline crack or a perished seal between cistern and pan, and then the water is going somewhere other than the bowl. Look for damp at the base and behindthe. pan
All of it falls under tap and toilet repairs, and on most cisterns it is a short job with a cheap part. The honest caveat is age. On a very old or obsolete cistern, the parts may no longer be made, and then it is a replacement conversation rather than a repair one.
Work Out What It Is Costing You
Every page on this subject quotes a litres-per-year figure. We have left it out, because we could not trace any of those numbers to a water utility, and you can measure your own in half an hour.
Turn off every tap and water-using appliance in the house, including the dishwasher, washing machine and any garden drip system. Write down your water meter reading. Leave the toilet alone and use no water for thirty minutes, then watch the meter and read it again.
Whatever moved is your running toilet, in litres, per half hour. Double it hourly,y, rate and the annual number is uncomfortable enough without anyone exaggerating it.
That is also the test that tells you whether the toilet is the only problem. If the meter moves more than the toilet can account for, something else is leaking too.
One thing not to count on. Sydney Water runs a hidden leak allowance for bills inflated by a leak, but a running toilet is neither hidden nor silent, so it is very likely outside it. Check their eligibility rules rather than assuming you will get a credit.
What You Can Do Yourself, and What You Cannot
Three things are reasonable to try before calling anyone.
Take the lid off and look at where the water level sits relative to the overflow tube and any fill line marked inside the cistern. If it is above the overflow, that alone explains a constant trickle.
Do the dye test, because knowing which valve it is halves the conversation.
And flush once, firmly, then let it settle. A button or lever that has not returned fully, or a chain or linkage caught on something, holds the outlet valve slightly open and mimics a failed seal exactly.
What is not worth doing is buying a universal kit and fitting it blind. Cistern internals vary a lot between brands and eras; the outlet seat matters as much as the seal, and a part that nearly fits leaks slowly enough that you will not notice for a month.
If water is overflowing out of the cistern rather than down the overflow, turn the isolation tap behind the pan clockwise until it stops, and call. That is the one version of this that will not wait.
Two answers and we know what to bring
Whether the dye reached the bowl, and roughly how old the toilet is. Those two tell us whether this is an outlet seal, an inlet valve or a cistern that has run out of spare parts. Call R&G on 0461 330 531. $0 call-out fee.
Frequently Asked Questions
Why does my toilet refill by itself when nobody has flushed it?
The outlet valve in the base of the cistern is no longer sealing, so water trickles continuously into the bowl. The level in the cistern slowly drops, the inlet valve detects it and tops it up, and you hear a refill. It is called a phantom flush, and it is usually a perished rubber seal.
How do I tell which part of my toilet is leaking?
Put a dozen drops of food colouring in the cistern, do not flush, and look in the bowl fifteen minutes later. Coloured water in the bowl means the outlet valve is passing. A clear bowl with water still running means the inlet valve is not shutting off and water is going over the overflow tube instead.
Is a running toilet an emergency?
No, unless water is coming out of the cistern rather than down the overflow tube. A normal running toilet wastes water without doing damage, so it waits for an ordinary appointment. If it is actually overflowing, turn the isolation tap behind the pan clockwise to shut it off and call.
How much water does a running toilet waste?
Measure yours rather than trusting a figure, because it depends entirely on how badly the valve is passing. Turn off every tap and appliance, read the water meter, use no water for thirty minutes, then read it again. Whatever moved is your toilet, and it is the only number that will tell you what the repair is worth.
Can I fix a running toilet myself?
You can check the water level against the overflow, do the dye test, and make sure the button or lever has returned fully, since a stuck linkage mimics a failed seal. Fitting parts blind is a different matter. Cistern internals vary between brands and eras, and the seat the seal sits on matters as much as the seal, so a nearly-right part leaks slowly enough that you will not notice for weeks.
Small part, short job
We service and repair cisterns, outlet and inlet valves, and replace toilets where the parts are no longer available, across the Upper North Shore, the Hills District and the Parramatta and Ryde corridor. Fixed price before anything starts, no call-out fee. See tap and toilet repairs, or emergency plumbing if a cistern is overflowing right now.
