How to Fix a Running Toilet

Reading time: 7-8 minutes

Skill level: Beginner

Cost: $0 – $25

A running toilet usually has a problem inside the tank. The flapper may not be sealing properly, the fill valve may not be shutting off, or the water level may be set too high.

Before buying a replacement part, you can usually narrow down the cause in about 10 minutes by watching what happens inside the tank and doing a simple food-colouring test.

Most running toilets can be fixed by replacing a worn flapper, adjusting the float, or replacing the fill valve. You usually don’t need to remove the toilet itself for these repairs.

Quick answer

Add a few drops of food colouring to the toilet tank and wait 10 minutes without flushing. If coloured water appears in the bowl, water is leaking from the tank into the bowl. If colored water appears in the bowl, water is leaking from the tank into the bowl. Inspect the flapper and its sealing surface first.

If the bowl stays clear, remove the tank lid and watch the water level as the toilet refills. If water continues flowing into the overflow tube, the tank should have stopped filling. Check the float and fill valve.

A loose or incorrectly adjusted chain, an incorrectly positioned refill tube, or mineral buildup around the flush valve can also prevent the toilet from shutting off properly.

A replacement flapper is usually inexpensive and can often be changed in about 10 to 15 minutes.

Item	Details
Time required	15 – 30 minutes
Skill level	Beginner
Estimated cost	$0 – $25
Common cause	Leaking or worn flapper
Tools needed	Gloves, towel, adjustable wrench or pliers

Signs your toilet is running

You may have a running toilet if:

You can hear water trickling into the bowl after flushing.
The toilet periodically refills when nobody has used it.
You hear a constant hissing sound from the tank.
Water continues flowing into the overflow tube.
The toilet seems to flush by itself.
Your water bill is higher than usual without an obvious change in water use.

A toilet that periodically refills on its own is often experiencing a slow leak from the tank into the bowl. This is sometimes called phantom flushing.

Diagnose the problem before replacing anything

Take the tank lid off and watch what happens after a flush.

What you notice	Likely problem	What to check
Water slowly enters the bowl after the tank fills	Leaking flapper or flush-valve seal	Inspect the flapper and sealing surface
Toilet periodically refills itself	Slow tank-to-bowl leak	Perform the dye test
Water rises into the overflow tube	Water level too high or a fill-valve problem	Check the float and fill valve
Hissing continues after the tank fills	Fill valve not shutting off properly	Check the float and fill valve
Flapper doesn’t close fully	Chain or handle adjustment	Check the chain and flapper

The food-colouring test is the easiest place to start.

Step 1: Test for a leaking flapper

This test tells you whether water is leaking from the tank into the bowl.

Remove the toilet tank lid.
Add several drops of food colouring to the tank water. You can also use a toilet leak-detection dye tablet.
Do not flush the toilet.
Wait about 10 minutes.
Look into the bowl.

If colored water appears in the bowl: Water is leaking from the tank into the bowl. Inspect the flapper and flush-valve sealing surface.
If the bowl stays clear: Check the water level, float, fill valve, and refill tube.

EPA recommends this same dye-test method for detecting toilet leaks.

Flush the toilet after testing so the dye does not stain the tank or bowl.

What you will need

For most running-toilet repairs, you won’t need much:

Rubber gloves
Towel or sponge
Replacement flapper, if required
Replacement fill valve, if required
Adjustable wrench or pliers

Before buying a replacement flapper, check the old part and the toilet’s model information. Flappers come in different sizes and designs, and not every replacement fits every toilet. Some manufacturers offer both universal and model-specific replacement parts.

Step 2: Replace the flapper if it is leaking

If the dye test shows water entering the bowl, start by inspecting the flapper.

A flapper is the rubber valve at the bottom of the tank. It lifts when you press the flush handle and then closes to hold water in the tank.

Over time, the rubber can become worn, stiff, or damaged and stop forming a good seal.

To replace it:

Turn the water supply valve behind the toilet clockwise until it stops.
Flush the toilet to drain most of the water from the tank.
Remove the chain from the flush lever.
Unhook the old flapper from the tabs or pegs on the flush valve.
Clean away any obvious mineral buildup from the sealing surface.
Install the replacement flapper.
Reconnect the chain, leaving enough slack for the flapper to close completely without the chain getting caught underneath it.
Turn the water supply back on.
Let the tank refill and flush the toilet.
Repeat the food-colouring test if you’re unsure whether the leak has stopped.

Don’t assume that a universal flapper will fit simply because it looks similar to the original. Check the size and compatibility with your toilet before installing it. Some universal models are designed to accommodate multiple flush-valve sizes, while others are intended for specific configurations.

Related: How to Replace a Toilet Flapper

Step 3: Check and adjust the float

If the flapper passes the dye test, watch the tank as it refills.

The water should stop rising before it flows continuously into the overflow tube.

If the water level rises too high, check the float.

Ball float

Older toilets may have a ball-shaped float attached to an arm. Depending on the valve design, adjusting the screw or float arm can lower the water level.

Cup float

Many newer fill valves use a cup-shaped float that slides along the fill valve. The adjustment method varies, but commonly involves an adjustment screw, clip, or other mechanism on the valve.

Lower the float slightly, then flush the toilet and watch the tank refill again.

Important: Don’t rely on a single water-level measurement for every toilet. Use the water-level mark inside the tank or the instructions for your fill valve when setting the final level.

Step 4: Replace the fill valve if it won’t shut off

If the fill valve needs replacing, see How to Replace a Toilet Fill Valve for a step-by-step walkthrough.

To replace the fill valve:

Turn off the water supply and flush the toilet.
Sponge out the remaining water from the tank if necessary.
Disconnect the water-supply line underneath the tank.
Remove the locknut securing the fill valve.
Lift the old fill valve out of the tank.
Adjust the replacement valve according to its installation instructions.
Insert the valve into the tank and tighten the locknut by hand.
Give the locknut the additional tightening specified by the valve manufacturer. Avoid overtightening.
Attach the refill tube using the supplied clip or fitting.
Reconnect the water-supply line.
Slowly turn the water supply back on.
Let the tank fill and check that the valve shuts off at the correct water level.
Flush the toilet several times and check for leaks.

The exact adjustment procedure varies between fill valves, so follow the instructions supplied with the replacement valve rather than using a single measurement as a rule for every model.

Check the refill tube

The small refill tube sends water into the toilet bowl after a flush. Its end should be positioned above the overflow tube opening rather than pushed down inside it.

If the refill tube is submerged or inserted too far into the overflow tube, it can allow water to siphon from the tank into the bowl after the toilet has finished filling.

Other causes of a running toilet

Not every running toilet needs a new part.

The chain is too tight

If the chain connecting the flush lever to the flapper has no slack, it can hold the flapper slightly open. Make sure the chain allows the flapper to close completely after the flush.

The chain is too loose

Too much slack can prevent the flapper from lifting properly or allow the chain to get caught underneath it.

Mineral buildup

Mineral deposits around the flush valve or its sealing surface can prevent the flapper from making a good seal.

If the flapper itself looks fine, clean the sealing surface before replacing additional parts.

The flush valve is damaged

If the sealing surface is cracked or badly damaged, replacing only the flapper may not solve the leak. At that point, the flush valve itself may need to be repaired or replaced.

How much water can a running toilet waste?

It depends on the size of the leak.

EPA WaterSense estimates that a small leaking toilet can waste about 860 gallons of water per month, while a medium leak can waste about 8,600 gallons per month. A large leak, such as one caused by a stuck fill valve, can waste about 4,300 gallons in a single day.

That is why even a toilet that only seems to trickle is worth fixing. The amount of wasted water can add up quickly.

How much does it cost to fix a running toilet?

If you can identify the problem yourself, the repair is usually inexpensive.

Repair	Typical DIY cost
Adjust float	$0
Replace flapper	About $5–$10
Replace fill valve	About $10–$20
Replace multiple tank components	About $15–$30

Prices vary by brand, toilet model, and where you buy the part.

When to call a plumber?

A running toilet is usually a manageable DIY repair, but get professional help if:

The porcelain tank or bowl is cracked
Water is pooling around the base of the toilet.
The flush valve or its mounting area is damaged.
You’ve adjusted or replaced the obvious tank components, and the toilet still runs.
You’re aren’t comfortable disconnecting the water supply or working inside the tank.
The problem appears to involve plumbing beyond the toilet tank.

If water is leaking onto the floor around the base, don’t treat that as simply another running-toilet problem. A leak there can have a different cause and may require a different repair.

FAQs

1. How do I know if the flapper is bad without food colouring?

While the toilet is running, gently press down on the flapper. If the running stops, the flapper may not be sealing correctly.

This is only a quick check, though. The dye test is more useful because it confirms whether water is actually moving from the tank into the bowl.

2. What is phantom flushing?

Phantom flushing is when a toilet periodically refills even though nobody has flushed it.

A slow leak from the tank into the bowl gradually lowers the tank’s water level. Once the level falls far enough, the fill valve turns on and refills the tank.

A leaking flapper is a common cause.

3. How often should a toilet flapper be replaced?

There isn’t one replacement interval that applies to every toilet. Flappers wear at different rates depending on the part, water conditions, and use.

EPA WaterSense recommends replacing toilet flappers at least every five years to help maintain a good seal.

However, there isn’t one replacement interval that applies to every toilet. Water conditions, the type of flapper, and how frequently the toilet is used can affect how long it lasts.

4. Should I replace the flapper and fill valve at the same time?

Not necessarily.

If one component is working properly, there’s no need to replace it simply because another part has failed. On an older toilet where both components are showing signs of wear, replacing both may make sense and can save you from doing the repair twice.

5. Why does my toilet keep running after replacing the fill valve?

If a new fill valve hasn’t solved the problem, check:

The flapper is sealing properly.
The float is adjusted correctly.
The refill tube is installed correctly.
The fill valve is adjusted according to its instructions.
The flush valve and sealing surface aren’t damaged.
The water supply pressure isn’t causing an issue with the particular valve.

If the tank is still losing water into the bowl, replacing the fill valve won’t fix the underlying leak.

6. Why does my toilet run intermittently?

An intermittently running toilet often has a slow leak from the tank into the bowl. The flapper may not be sealing completely, allowing the tank level to gradually fall. When the level drops far enough, the fill valve turns on and refills the tank. This cycle can repeat even when nobody has flushed the toilet.

How to Replace a Toilet Flapper
How to Replace a Toilet Fill Valve
How to Stop a Toilet from Overflowing
The Complete Guide to Home Plumbing

Sources

EPA WaterSense: Residential Toilets and Home Maintenance guidance on toilet leaks and the dye test.
EPA WaterSense: Leak-loss estimates for leaking toilets.
Korky: Toilet flapper sizing and universal/model-specific compatibility information.