Fix a running toilet
Save £80–150 today
1 hour · Beginner · Saves £80-150 vs a plumber
Last updated: February 2025
Before you start
A running toilet constantly trickles water into the bowl after flushing. This is almost always caused by a faulty flapper valve or a misadjusted float arm — both are cheap and easy to fix.
You will need to look inside the cistern (the tank at the back of the toilet). It is just water — nothing unpleasant.
Tools needed
- ✓Towel or cloth — to set the cistern lid on and catch any drips
- ✓Screwdriver — needed for some cistern types to adjust the ballvalve
- !Replacement flapper valve — buy only if needed: £5–15, take the old one to the shop to match the size
Remove the cistern lid
Lift the lid off the cistern and set it aside on a towel. Look inside — you will see the float (a ball or cup on an arm), the fill valve, and the flapper at the bottom.
Where beginners go wrong
Not turning off the isolation valve before replacing the flapper, leading to water everywhere.
Buying the wrong size flapper — take the old one to the shop to match it.
Setting the float too low, so the cistern does not fill enough to flush properly.
Stop and call a plumber if...
There is water leaking around the base of the toilet
The cistern will not stop filling even after adjusting the float
The isolation valve will not turn off the water supply
Cost breakdown
What you just learned
You now understand how a toilet cistern works — the float, fill valve, and flapper. These skills transfer to replacing a full ballvalve, fixing a slow-filling cistern, and understanding your home's water system.
✅ Completed by 1,247 people
⚠️ Watch out if you rent
Landlords are legally responsible for keeping toilets in working order. Report it in writing first. If they fail to act within a reasonable time (14 days for non-emergencies), contact your local council's Environmental Health department.
How long will this actually take me?
First time
1–1.5 hours
With experience
30 mins
Spend 5 minutes understanding the cistern parts before you start — it saves a lot of guessing.