A leaking toilet tank can be a frustrating and wasteful problem for homeowners. When water escapes from the tank during flushing, it not only leads to higher water bills but also indicates an underlying issue that requires attention.

Understanding the causes of a toilet tank leaking when flushed and implementing the appropriate solutions is essential to prevent water waste and potential damage.

In this article, we will explore the common causes of this problem and provide practical troubleshooting tips to help resolve the issue.

Identifying the Causes of a Toilet Tank Leaking When Flushed:

  1. Faulty Flapper or Flushing Mechanism: The flapper is a rubber valve that controls the release of water from the tank to the bowl during flushing. If the flapper is worn out, damaged, or improperly aligned, water can escape from the tank. Similarly, a faulty flushing mechanism, such as a broken or misaligned handle, can lead to water leakage. Inspect the flapper and flushing mechanism for any signs of damage or misalignment.
  2. Loose or Damaged Tank Bolts: Tank bolts secure the toilet tank to the bowl. If these bolts are loose or damaged, water may leak from the tank. Check the tank bolts for tightness and replace them if they are corroded or damaged.
  3. Cracked Tank or Bowl: A crack in the tank or bowl can cause water to leak when the toilet is flushed. Inspect the tank and bowl for any visible cracks or signs of damage. If a crack is detected, the affected component will likely need to be replaced to resolve the issue.
  4. Faulty Fill Valve or Float Assembly: The fill valve and float assembly regulate the water level in the tank after flushing. If the fill valve is not shutting off properly or the float assembly is malfunctioning, water may continue to flow into the tank, leading to leakage. Adjust or replace the fill valve and float assembly as necessary.
  5. Improperly Sealed Flush Valve: The flush valve is responsible for the release of water into the bowl during flushing. If the flush valve is not properly sealed, water may leak from the tank. Check the seal around the flush valve and ensure it is tight and in good condition. Replace the seal if necessary.

Troubleshooting Steps to Resolve the Issue:

  1. Turn off the Water: To prevent further water waste and potential damage, turn off the water supply to the toilet by shutting off the supply valve located behind or near the toilet.
  2. Inspect and Clean the Flapper: Examine the flapper for any signs of wear, damage, or misalignment. Clean it to remove any debris that may be preventing it from creating a proper seal. If necessary, replace the flapper with a compatible one.
  3. Check and Tighten Bolts: Inspect the tank bolts for tightness. Use a wrench to tighten them if they are loose. Replace any bolts that are corroded or damaged.
  4. Examine for Cracks: Thoroughly inspect the tank and bowl for cracks or damage. If a crack is found, consider replacing the affected component.
  5. Adjust or Replace Fill Valve and Float Assembly: Ensure that the fill valve is shutting off properly and that the float assembly is functioning correctly. Adjust or replace these components if needed.
  6. Verify the Flush Valve Seal: Check the seal around the flush valve and ensure it is properly sealed. Replace the seal if it is worn out or damaged.


A toilet tank leaking when flushed can waste water and indicate an underlying issue that requires attention. By identifying the causes and implementing the appropriate solutions, homeowners can resolve this problem effectively.

Regular maintenance and prompt repairs are key to preventing water waste and ensuring the efficient operation of the toilet.