How to fix a toilet that keeps running
It is almost always one of two cheap parts: the flapper is not sealing, or the fill valve is set too high or has failed. Lift the tank lid and look — if water is spilling into the overflow tube, it is the fill valve; if the tank is slowly draining with no visible overflow, it is the flapper. Both are under $20 and take about twenty minutes.
- Difficulty
- Easy
- Time
- 20–45 minutes
- Parts cost
- $10–$25 in parts
- Trade
- Plumbing
What you need
- Adjustable wrench
- Sponge and bucket
- Replacement flapper or fill valve
Step by step
- 01
Work out which one it is
Take the lid off and watch. Water trickling into the open-topped overflow tube in the middle means the fill valve is letting the level rise too high. No overflow, but the water level slowly dropping and the valve kicking on every few minutes, means the flapper is leaking.
- 02
The quick test for a leaking flapper
Put a few drops of food coloring in the tank and do not flush for thirty minutes. Color in the bowl means the flapper is passing water. This is the single most common cause and the cheapest fix in plumbing.
- 03
If it is the fill valve, try adjusting first
Most modern fill valves adjust with a screw or a clip on the float. Set the water line about an inch below the top of the overflow tube. If it will not hold a setting, the valve is done — replace it rather than fighting it.
- 04
Replacing a flapper
Shut off the supply, flush to empty the tank, sponge out the rest. Unclip the old flapper, take it to the store and match it — flappers are not universal. Clip the new one on, hook up the chain with about half an inch of slack, and test.
- 05
Replacing a fill valve
Same start: water off, tank empty. Disconnect the supply line underneath, undo the lock nut, lift the old valve out. Set the new one to the right height before installing, fit it, reconnect and adjust the level. Twenty minutes if nothing is seized.
Stop and call somebody if…
- Water is coming from under the tank or around the base of the toilet, not from inside the tank
- The tank bolts or the supply nut are rusted solid
- The toilet rocks when you sit on it — that is a flange or a wax ring, not a fill valve
- You have replaced both parts and it still runs
A running toilet is genuinely a DIY job and we would rather you fixed it yourself. Water at the base of the toilet is a different problem and it is one worth calling about.
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