A toilet that keeps running after flushing wastes a surprising amount of water and can noticeably increase a water bill over time. The cause is almost always one of two components inside the cistern, both of which are straightforward to check and replace.
How Do You Fix a Running Toilet?
To fix a running toilet, remove the cistern lid and check the flapper valve for a poor seal, and check the float and fill valve for the correct water level, adjusting or replacing whichever component is causing water to continuously flow. These two parts account for the vast majority of running toilet problems.
What You Will Need
- Rubber gloves
- A replacement flapper valve or fill valve, if needed, matched to your cistern type
- An adjustable spanner
- A towel
How to Fix a Running Toilet: Step by Step
1. Remove the Cistern Lid
Lift the cistern lid off carefully and set it somewhere safe, since it is often heavier and more fragile than it looks.
2. Check the Flapper Valve
The flapper valve sits at the base of the cistern and controls water flowing into the bowl. If it does not seal properly, water leaks through continuously, causing the fill valve to keep topping up the cistern. Look for visible wear, warping, or mineral buildup preventing a tight seal.
3. Clean or Replace the Flapper
If the flapper is dirty, clean it and the valve seat it sits on with a cloth, then test again. If it is cracked, warped, or worn, replace it with a new one matched to your cistern, which is an inexpensive and straightforward swap.
4. Check the Water Level
Most cisterns have a marked water level line. If water sits above this line, it may be continuously draining into the overflow tube, causing the fill valve to run constantly to compensate.
5. Adjust the Float
For a ball float, gently bend the arm downward slightly to lower the water level. For a cup-style float, adjust the clip or screw mechanism according to your specific fill valve design, lowering it until the water level sits at the marked line.
6. Check the Fill Valve
If adjusting the float does not resolve the issue, the fill valve itself may be worn or faulty. These are generally inexpensive to replace and involve turning off the water supply, draining the cistern, and swapping the unit following the manufacturer’s instructions.
7. Test the Fix
Flush the toilet and listen for a few minutes afterward to confirm the running has stopped and the cistern settles at the correct water level.
Why This Matters Beyond the Noise
A running toilet can waste hundreds of litres of water a day, which adds up noticeably on a metered water bill over time. Fixing it promptly is one of the more cost-effective small repairs available in a home.
If you are dealing with other small plumbing jobs at the same time, our guide to fixing a dripping tap covers another common and similarly straightforward fix.
Frequently Asked Questions
Why does my toilet keep running after I flush?
A worn or poorly sealed flapper valve is the most common cause, letting water continuously leak into the bowl and triggering the fill valve to keep refilling the cistern.
How much water does a running toilet waste?
A persistently running toilet can waste several hundred litres of water a day, which is a significant amount over time, particularly on a metered water supply.
Can I fix a running toilet without replacing any parts?
Sometimes, yes. Cleaning the flapper valve or adjusting the float to correct the water level can resolve the issue without needing new parts, though a worn flapper or fill valve will eventually need replacing.
How do I know if it is the flapper or the fill valve?
If water is visibly leaking past the flapper into the bowl even when the cistern is not being used, the flapper is the likely cause. If the water level in the cistern sits too high and constantly drains into the overflow, the fill valve or float adjustment is more likely the issue.
Is fixing a running toilet a DIY job?
Yes, in most cases. Both flapper and fill valve replacement are common, inexpensive DIY repairs that do not require specialist plumbing skills, provided you turn off the water supply before starting any parts replacement.
Always turn off the water supply to the toilet before replacing any internal cistern parts, and check compatibility with your specific toilet model before purchasing replacements.
About the Author
Spire Homes Editorial Team researches and writes practical, UK focused home improvement guides covering renovation planning, financing, interior design, and property maintenance. Our content is reviewed for accuracy and updated as guidance changes.
