A toilet that never quite stops filling
It is almost always one of four things inside the tank, and there is a test that proves which in half an hour without tools.
If your toilet has no tank, this is not your fault to find
Every guide to this describes the same repair: take off the tank lid, check the flapper, adjust the fill valve, shorten the chain. Home Depot opens by telling you to turn off the supply and hold the handle down.
A pail-flushed bowl has no tank, no flapper and no fill valve. It cannot run. If water is moving in your house with nothing being used, it is the supply line, a tank somewhere else or a fitting, and the meter will find it faster than the bathroom will.
The test that settles it
Put a few drops of food colouring in the tank. Leave it half an hour and do not flush. Then look in the bowl.
Colour in the bowl means the flush valve seal is passing, and that is your leak. No colour means the tank is not leaking into the bowl and you should be looking at the fill valve and the overflow instead. It costs nothing and it needs no tools.
The four things it is
The flapper or flush valve seal
The rubber seal at the bottom of the tank has hardened or warped, so it no longer seats. The most common cause by a wide margin, the cheapest part, and the one the food colouring test proves.
The chain is too short or too long
Too short and it holds the flapper slightly open. Too long and it tangles under the flapper. Both cause the same symptom and neither needs a new part.
The fill valve will not shut off
The tank fills past its mark and pours down the overflow tube forever. You can see this one: look for water running into the open pipe in the middle of the tank.
The float is set too high
The same result as a failed fill valve, from a different cause. The water level should sit about an inch below the top of the overflow tube, and the float is adjustable.
Here, the symptom is often the pump
This is the part no other page on the subject will tell you, because it assumes a pressurised mains supply.
If your house is fed from a roof tank, a leaking flush valve does not announce itself as a noise in the bathroom. It drains the roof tank quietly, and the pump refills it. So what you actually notice is the pump cutting in at two in the morning, or the tank never staying full. Same fault, completely different symptom, and it is the most common reason a bill goes up with nothing visibly dripping anywhere.
Where it stops being a part you can change
- A new flapper that still passes, which usually means the seat it sits on is pitted or scaled rather than the rubber being at fault.
- Water at the base of the bowl rather than inside the tank. That is the wax seal or the closet flange, and it is a different job that involves lifting the toilet.
- A concealed cistern behind a wall or inside a vanity, where getting to the parts is most of the work.
- A pump that is short cycling after the toilet is fixed. That is the pump or its pressure tank, and if the fault is electrical it is an electrician's work rather than ours.
Questions about a toilet that keeps running
- My toilet has no tank. Can it still run?
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No, and that is worth knowing before you go looking. A pail-flushed bowl has no tank, no flapper and no fill valve, so there is nothing to leak from and nothing to keep refilling. If water is moving somewhere with nothing being used, it is coming from the supply line, a tank elsewhere in the house, or a fitting, not from the bowl.
- How do I prove it is the toilet without taking anything apart?
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Put a few drops of food colouring in the tank, leave it half an hour without flushing, then look in the bowl. If the colour has arrived in the bowl, the flush valve seal is passing and that is your leak. It costs nothing, takes no tools, and it is the one test that settles the argument.
- Why does my pump keep starting when nobody is using water?
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On a house fed from a roof tank, a leaking flush valve drains that tank quietly, and the pump refills it. So the symptom you notice is not a running toilet but a pump cutting in at two in the morning. It is the same fault, and it is the reason a high bill often has no visible drip anywhere in the house.
- What does a running toilet actually waste?
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Far more than a dripping tap, which is why it is worth chasing. A flush valve passing steadily can lose several litres an hour, so the number to check is your meter rather than your intuition. Take two readings with nothing in use and work out the rate before assuming it is small.
Silent, and the most expensive one
A running toilet wastes more than anything else in a house and makes no noise doing it. Ring us and say what the colouring test showed.
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