For homeowners, a leaky toilet tank may be an irritating and expensive issue. When water leaks when flushing, it not only results in higher water bills but also suggests a more serious problem that has to be addressed.

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 post, we’ll examine some of the typical root causes of this issue and offer useful troubleshooting advice to help you fix it.

Identifying the Causes of a Toilet Tank Leaking When Flushed:

  1. Faulty Flapper or Flushing Mechanism: During flushing, a rubber valve called a flapper regulates the flow of water from the tank into the bowl. Water may leak from the tank if the flapper is damaged, worn out, or misaligned. Similar to the last example, a damaged or improperly aligned handle on a flushing device might cause water to spill. Examine the flapper and flushing mechanism for any indications of deterioration or alignment issues.
  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. Flush Valve Not Properly Sealed: When flushing, water is released into the bowl through the flush valve. Tank water may leak if the flush valve is not correctly shut. Make sure the seal surrounding the flush valve is tight and in good shape by inspecting it. If necessary, swap out the seal.

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.


When flushed, a toilet tank that leaks can waste water and be a sign of a more serious problem. Homeowners can successfully fix this issue by pinpointing the root reasons and putting the right solutions in place.

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