Why Does My Toilet Keep Running After Flushing?
For a toilet that continues trickling, hissing or refilling after the flush should have finished, including water running into the pan.
What this usually means
A toilet that keeps running after flushing usually has a cistern fault rather than a drainage blockage. Common causes are a flush valve that is not sealing, a fill valve that does not shut off, or a water level that is high enough to spill into the overflow. Watching the cistern refill and checking whether water continues to enter the bowl normally reveals which part is responsible.
What may be causing this
Flush valve is not sealing
Clues: The cistern reaches its normal level but water still trickles into the pan, or the water level in the cistern slowly falls after filling.
What to do: Inspect the flush-valve seal for dirt, damage, distortion or poor seating. Clean or replace the seal/valve with the water isolated if the part is serviceable.
Fill valve does not shut off correctly
Clues: The cistern keeps taking in water, you hear continuous hissing, or water reaches the overflow instead of stopping at the intended level.
What to do: Check the float and fill valve move freely and that the shut-off level is set correctly. A worn or sticking fill valve may need adjustment or replacement.
Water level is too high
Clues: Water visibly enters the overflow tube or internal overflow once the cistern is full.
What to do: Adjust the fill level according to the cistern or valve manufacturer's instructions so the water stops below the overflow.
Debris or limescale is preventing a valve from closing
Clues: The problem is intermittent, the valve feels sticky, or the seal surface has visible deposits.
What to do: With the water isolated, clean accessible valve/seal surfaces if the manufacturer permits. Replace damaged parts rather than forcing them.
How to check what is happening
The cistern is leaking water into the bowl and should be investigated rather than treated as normal post-flush water.
The fill valve or fill-level adjustment is the likely problem.
The flush valve is likely allowing water to escape into the bowl.
Can you fix this yourself?
A visible, accessible cistern can often be diagnosed by a homeowner. Simple float adjustments, cleaning a seal or replacing a compatible flush/fill valve may be reasonable DIY work if the water can be isolated and the cistern manufacturer's instructions are followed.
- Torch
- Old towel
- Screwdriver if required by the cistern
- Replacement seal or valve only after identifying the fitted type
What you can safely try
- 1
Confirm that water is still entering the bowl
After a flush, allow the cistern enough time to refill. Look for a continuing trickle or ripple at the back of the pan. A persistent flow means the cistern is passing water.
- 2
Check the water level and overflow
If the lid can be removed safely, watch the refill cycle. The inlet should stop before water enters the overflow. If it does not, check the float and fill-level adjustment before replacing parts.
- 3
Inspect the flush and fill valves
Isolate the toilet water supply before removing parts. Check that the flush-valve seal sits cleanly and that the fill-valve float moves freely. Clean accessible deposits or replace worn compatible parts according to the valve instructions.
- 4
Restore the water and test several flushes
Turn the supply back on slowly, let the cistern fill and flush several times. Confirm that filling stops consistently and that no water continues to run into the bowl.
Call a plumber if…
- The toilet has a concealed cistern you cannot access without disturbing fixed panels or finishes.
- The isolation valve will not close or starts leaking.
- The cistern, pan or connector is cracked or leaking onto the floor.
- You cannot identify compatible replacement parts or the running water continues after adjustment/replacement.
Get the right plumber.
We already know this problem maps primarily to a plumber. Choose the closest type of work, add your postcode and continue in the form.
Sources used for this guide
We prefer primary UK guidance, regulators and manufacturers for technical and safety-sensitive claims.
- How do you stop a running toilet?WaterSafe Register
- Identifying leaksThames Water
Last reviewed: 31 August 2026. Home Manual updates review dates only when the substance of a guide is checked or changed.