How to Fix a Running Toilet (Step-by-Step DIY Guide)
1. How to Diagnose the Problem
Take the tank lid off and look inside. A running toilet is one of two things:
- Water spilling into the overflow tube (the vertical pipe in the center) — your float is set too high.
- Water level is below the overflow tube, but you hear trickling — your flapper is leaking.
The water level should sit about 1 inch below the top of the overflow tube.
2. Fix: Float Set Too High (Free, 2 Minutes)
- Find the float mechanism on the fill valve (left side of tank).
- Ball float: Bend the arm slightly downward, or turn the adjustment screw.
- Cup float: Pinch the clip and slide the float down about 1/2 inch.
- Flush and watch. Water should stop about 1 inch below the overflow tube.
If adjusting the float doesn't change the water level at all, the fill valve itself is failing and needs replacement.
Here's how homemd.ai diagnoses this problem
Describe your toilet issue or upload a photo. homemd.ai identifies the exact cause and walks you through the fix with the right parts.
Get Your Free Diagnosis3. Fix: Leaking Flapper (Under 30 Minutes)
- Turn off the water valve behind the toilet (turn clockwise).
- Flush to empty the tank.
- Unhook the old flapper from the two pegs on the overflow tube.
- Hook the new flapper onto the same pegs.
- Attach the chain with about 1/2 inch of slack.
- Turn the water back on and test flush.
4. Parts You'll Need
Korky 2003BP 3-Inch Universal Toilet Flapper — ~$8 — View at Home Depot
Fluidmaster 400A Universal Fill Valve — ~$12 (only if float adjustment fails) — View at Home Depot
5. Cost Breakdown: DIY vs Plumber
| Option | Cost | Time |
|---|---|---|
| DIY — Flapper only | $8–$12 | 15–30 min |
| DIY — Flapper + Fill Valve | $20–$30 | 30–45 min |
| Plumber | $120–$250 | Same day |
You save $100–$240 doing this yourself.
6. When to Call a Plumber Instead
- You replaced both flapper and fill valve but it still runs.
- Water leaking from the base of the toilet (wax ring issue).
- The tank has visible cracks.
FAQ
Why won't my toilet stop running?
Almost always a leaking flapper ($8) or float set too high (free fix). Take the tank lid off to diagnose.
How much does a plumber charge to fix a running toilet?
$120 to $250 including service call and parts. DIY cost: $8 to $25.
When should I call a plumber instead of fixing it myself?
Call a plumber if you replaced both the flapper and fill valve but it still runs, water is leaking from the base, or the tank has visible cracks.
Watch: Fix a Running Toilet - Fill Valve Replacement
Frequently Asked Questions
Why won't my toilet stop running?
A running toilet is almost always caused by either a leaking flapper valve ($8 to replace) or a float set too high (free to adjust). Take the tank lid off: if water is spilling into the overflow tube, lower the float. If the water level is normal but you hear trickling, replace the flapper.
How much does a plumber charge to fix a running toilet?
A plumber typically charges $120 to $250 for a running toilet repair, including a service call fee and parts. The same fix costs $8 to $25 in parts if you do it yourself.
When should I call a plumber instead of fixing it myself?
Call a plumber if you replaced both the flapper and fill valve but it still runs (could be a cracked overflow tube), water is leaking from the base of the toilet (wax ring issue), or the tank has visible cracks.
Related Guides
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