How to diagnose and fix a toilet that keeps running
A toilet that refills every few minutes or sends a constant trickle into the bowl is usually losing water through the flush valve or admitting too much through the fill valve. Modern concealed cisterns and older siphon systems differ, so identify what you can access before buying a replacement part.
Start by listening and observing. Do not apply sealant inside the cistern or bend components to make them fit. Most reliable repairs involve cleaning, adjusting or replacing the correct service part.
Find out which valve is responsible
Remove the cistern lid carefully and place it somewhere padded. Mark the current water level with a pencil, close the toilet's isolation valve and wait 20 to 30 minutes without flushing. If the level falls and water appears in the bowl, the flush seal is likely passing. If the level stays put but rises too high when the supply is reopened, inspect the fill valve and float setting.
Some cisterns send overflow water internally into the bowl rather than through an outside pipe. A high water line and continuous bowl trickle can therefore indicate a fill valve that does not shut off.
Check the float and fill valve
- Make sure the float moves freely and is not touching the cistern wall.
- Remove obvious grit only according to the valve manufacturer's service method.
- Use the designed screw or clip to set the shut-off level below the overflow point.
- Replace the fill-valve diaphragm or complete valve if it still fails to close consistently.
Isolate the supply and flush before removing any valve part. Support the pipe and valve so turning a nut does not twist the supply connection below the cistern.
Inspect the flush valve seal
On many dual-flush toilets, the central flush tower releases with a short twist once the cistern is empty. Photograph its position first. Check the rubber seal for grit, scale, distortion or blisters, and clean the mating surface gently. Replace the seal with the exact diameter and profile if it no longer sits flat.
If the flush buttons remain pressed, reconnect or adjust their rods or cables according to the cistern design. A button that holds the valve slightly open can mimic a failed seal.
When a plumber is the better repair
Use a plumber when the isolation valve is seized, the cistern is concealed with poor access, fittings are corroded, the ceramic is cracked, water appears around the pan, or replacement parts cannot be identified. Do not overtighten fixings against ceramic.
Useful job post: 'Close-coupled dual-flush toilet in Limerick runs into the bowl every few minutes. With the inlet isolated, the cistern level drops, so the flush seal appears to be passing. The service valve works and there is no water on the floor. Photos show the cistern internals and button. Please quote to supply and fit the correct seal or flush valve and test the inlet and pan connections.'
Frequently asked questions
Why does my toilet refill when nobody has used it?+
Water is probably escaping slowly from the cistern into the bowl, causing the fill valve to reopen. A worn or dirty flush seal is a common cause.
Can I use sealant on a leaking flush valve?+
Sealant is not a dependable substitute for the correct internal seal and may obstruct the mechanism. Clean or replace the designed service part.
Why does the toilet keep running after I press the button?+
The button, cable or rod may be holding the flush valve open, or the valve may not be seating because of scale, debris or a damaged seal.
Can a plumber repair a concealed cistern?+
Usually, serviceable parts are reached through the flush-plate opening. Include the brand, plate dimensions and access photos in your job post.
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