A toilet should refill after flushing and then become quiet. If you hear water trickling, see ripples in the bowl or notice the cistern refilling when nobody has used the toilet, you may have a continuous leak.
When a toilet keeps running, a seal, valve, float or flush mechanism inside the cistern may not be working correctly. Although the toilet may still flush normally, a small internal leak can waste water continuously.
The good news is that many running toilet problems can be repaired without replacing the entire toilet. Here are six common causes to check.
Quick Answer: Why Does a Toilet Keep Running?
A toilet keeps running when water is either continuously entering the cistern or escaping from the cistern into the toilet bowl.
The inlet valve controls the flow of fresh water into the cistern, while the outlet valve and seal control the water released into the bowl during a flush. If either system fails to shut off correctly, the cistern may continually refill.
A quiet trickle can continue for hours between flushes, making a running toilet an easy problem to overlook.
Signs Your Toilet Is Leaking Between Flushes
A running toilet does not always make a loud or obvious noise. Look and listen for:
- A faint hiss or trickling sound after flushing
- The cistern briefly refilling when nobody has used the toilet
- Ripples or movement in the toilet bowl
- A faint stream of water running down the back of the bowl
- The water level reaching or entering the overflow
- Higher-than-usual water usage without an obvious explanation
You can also place a small piece of dry toilet paper against the inside back of the bowl. If it becomes wet between flushes, water may be leaking from the cistern into the bowl.
Cause 1: The Outlet Washer or Seal Is Worn
The outlet valve releases water from the cistern into the bowl when you flush. Once the flush is complete, a rubber washer or seal should close the opening and prevent further water from escaping.
Over time, the rubber can become hard, warped, cracked or coated with mineral residue. When it no longer forms a proper seal, water slowly leaks into the bowl.
The inlet valve then opens to replace the lost water. If your toilet keeps running even though the cistern appears to be full, the outlet seal is one of the first components worth checking.
Replacing the seal may solve the problem if the valve body and valve seat are still in good condition.
Cause 2: The Inlet Valve Is Not Shutting Off
The inlet valve controls fresh water entering the cistern. It should open after a flush and then shut off once the water reaches the correct level.
An ageing, dirty or damaged inlet valve may stick or fail to close completely. Water can then continue flowing into the cistern and eventually discharge through the internal overflow into the bowl.
A steady hissing sound or visible water entering the overflow can indicate an inlet valve problem.
Depending on its condition, a plumber may be able to clean or adjust the valve. If it is worn or damaged, replacement may be the better option.
Cause 3: The Float Is Stuck or Set Too High
The float tells the inlet valve when the cistern has reached the correct water level. Depending on the toilet design, it may be a traditional ball float attached to an arm or a compact float incorporated into the inlet valve.
If the float is set too high, the cistern may continue filling until water reaches the overflow. A float can also become stuck, rub against the cistern or catch on another component.
The adjustment may have changed over time, or the float assembly itself may be worn.
Correct adjustment should allow the cistern to fill sufficiently for a proper flush without allowing water to enter the overflow. Avoid forcing old or brittle components, as they can break.
Cause 4: The Flush Button, Lever or Chain Is Sticking
The flush mechanism should lift the outlet valve and then release it fully. If the flush button remains partially pressed or the internal mechanism does not return correctly, the outlet seal may stay slightly open.
Common problems include:
- A stiff or misaligned flush button
- A lever that does not return properly
- A chain that is too tight
- A chain that has become tangled
- A worn or damaged flush mechanism
The problem may be intermittent, which means pressing or moving the flush button again may temporarily stop the running water.
A plumber can inspect the mechanism, adjust the linkage and replace worn components where necessary.
Cause 5: Debris or Mineral Build-Up Is Preventing a Proper Seal
A rubber washer or seal cannot close properly if dirt, grit or mineral deposits have collected around the valve seat.
Small particles can enter the water supply during plumbing work or accumulate inside the cistern over time. Mineral deposits can create an uneven surface, allowing water to slowly pass into the bowl.
If your toilet keeps running intermittently, debris may be preventing the seal from closing correctly after certain flushes.
Cleaning may resolve a minor build-up problem, but damaged seals or valve surfaces may require replacement.
Avoid using harsh drain chemicals inside the cistern. They are not designed to repair mechanical toilet components and may damage rubber seals and other parts.
Cause 6: Internal Parts Are Damaged or Incorrectly Fitted
Sometimes the problem is caused by a damaged valve body, cracked component, worn valve seat or brittle plastic fitting.
Incorrect replacement parts can also cause ongoing problems. A washer that looks similar may not create the correct seal, while an incorrectly sized inlet valve can affect the water level and overflow.
Older cisterns may also have several ageing components. Replacing one washer may temporarily improve the problem without addressing other worn parts.
In these situations, a complete inspection and internal service may provide a more reliable long-term solution.
What Can You Safely Check?
There are a few simple checks you can carry out without dismantling the toilet.
Listen after the cistern has finished refilling. Look for movement in the toilet bowl and check whether the water level changes between flushes.
You can also check that:
- The flush button or lever returns to its normal position
- The cistern water level is not visibly reaching the overflow
- The toilet is not continuously refilling
- There is no water around the base of the toilet
- The isolation valve is accessible and operating normally
If the cistern lid lifts easily, you can inspect the water level without forcing any components.
Concealed cisterns require extra care because the internal mechanism may only be accessible through a specific access panel. Do not force the panel or attempt to dismantle components you cannot identify.
If the toilet is running heavily and the isolation valve operates freely, turning off the water supply can reduce water loss while you arrange professional assistance.
Never force a stiff or corroded isolation valve, as it may break and create a larger leak.
Why Does a Running Toilet Sometimes Stop and Start?
A toilet does not necessarily have to run continuously to have a leak.
Some leaks are slow enough that the cistern loses water gradually. Once the water level drops, the inlet valve opens briefly to refill it. This can create a cycle of occasional hissing or refilling.
This is sometimes called phantom flushing or ghost flushing and is commonly associated with a leaking outlet seal.
Even if the toilet becomes quiet again, the underlying leak should still be investigated.
When Should You Call a Plumber?
Arrange a plumbing inspection if:
- The toilet trickles or hisses after every flush
- The cistern repeatedly refills by itself
- Water is entering the overflow
- The toilet continues running after basic checks
- The cistern is concealed
- The isolation valve is damaged or difficult to operate
- The toilet has several old or worn internal components
Water on the bathroom floor, around the base of the toilet or inside a wall should be treated more urgently. This may indicate a different leak from a seal, connection, pipe or toilet pan.
If you cannot safely isolate a significant leak, arrange prompt professional assistance rather than attempting to dismantle the toilet yourself.
How Does a Plumber Diagnose a Running Toilet?
A plumber will inspect the toilet’s internal components to identify where the water is coming from and why the cistern is not shutting off correctly.
Depending on the toilet, this may include checking:
- The inlet valve
- The outlet valve and seal
- The float and water level
- The overflow
- The flush button or lever
- Internal linkages
- Valve seats and connections
- The toilet isolation valve
- The water supply connection
The correct repair depends on the toilet model, the condition of its components and the availability of compatible replacement parts.
Professional diagnosis helps identify the actual cause before parts are replaced unnecessarily.
Should You Repair or Replace the Toilet?
Most running toilet problems can be repaired by adjusting, cleaning or replacing individual cistern components.
Replacement may be more appropriate if the toilet is cracked, repeatedly develops faults, is very old or has obsolete components that are difficult to source.
Replacing the toilet can also make sense as part of a wider bathroom renovation or upgrade.
A qualified plumber can assess the condition of the existing toilet and help you compare the cost of repair with replacement.
Don’t Let a Small Toilet Leak Run Around the Clock
A running toilet rarely fixes itself. Even a quiet trickle can continue for hours between flushes, wasting water and potentially becoming more noticeable over time.
If your toilet hisses, trickles, refills by itself or shows unexplained movement in the bowl, it is worth having the problem checked.
Early repairs can often be as simple as adjusting a float or replacing a worn seal. Identifying the problem sooner can also prevent a minor cistern fault from becoming a more significant plumbing issue.
About Tai Irwin Plumbing and Draining
Tai Irwin Plumbing and Draining provides professional plumbing services across Sydney’s Northern Beaches and North Shore for homeowners, businesses, strata properties and real estate clients.
Our experienced team can assist with running toilets, leaking toilets, blocked drains, leaking taps, burst pipes, hot water problems and other plumbing issues. 24-hour emergency plumbing support is also available when urgent assistance is required.
If your toilet keeps running, contact Tai Irwin Plumbing and Draining for professional diagnosis, fixed-price repair options and workmanship backed by our Total Work Guarantee.
