Symptoms
- Water audibly runs into the overflow tube
- Tank water sits very close to the lid
- Toilet runs constantly or intermittently
- Water bill has increased
Likely causes
- CommonFloat set too highThe float arm or cup hasn't been adjusted down, so the fill valve keeps letting water in past the safe level.
- CommonFill valve not shutting offA worn fill valve mechanism fails to stop the flow at the correct level.
- PossibleWrong fill valve height for the tankA replacement fill valve installed too tall can overfill the tank.
What to do
- Remove the tank lid and watch where the water level stabilizes relative to the overflow tube.
- For a float-cup valve, pinch the clip and slide the float down an inch, then test.
- For an older float-ball valve, gently bend the float arm downward slightly.
- Flush and observe the new fill level; it should land about an inch below the top of the overflow tube.
- Replace the fill valve if adjusting the float doesn't bring the level down or the valve keeps running past shutoff.
- Recheck after a few flushes to confirm the level holds steady.
Tools and parts
- Adjustable wrench (if replacing valve)
Toilet fill valveSearch: “universal toilet tank fill valve”
When to call a pro
A plumber visit is rarely needed unless a new fill valve still overfills the tank, which can point to a tank sizing mismatch.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.