A running toilet is one of those problems that seems small… until you hear it filling all night or see your water bill spike. The constant sound of water refilling the tank usually means something inside the toilet isn’t sealing or functioning properly — and the good news is, most of the time, it’s a quick DIY fix.
In this guide, I’ll walk you step-by-step through how to diagnose and fix a running toilet, even if you have zero plumbing experience.
If you’re working on other bathroom issues too, check out our related guides in Plumbing Fixes and Cleaning & Care.
Why Your Toilet Keeps Running
A toilet that keeps running usually comes down to one of four common causes:
- A loose or misaligned flapper
- A damaged or worn-out flapper
- A faulty or misadjusted fill valve
- An improperly set float
Let’s break each one down and fix them.
Step 1: Identify Where the Problem Is
First, remove the tank lid and set it aside carefully (porcelain cracks easily).
Now flush the toilet and watch closely as the tank refills.
Here’s what to look for:
- Does water keep trickling into the bowl after filling?
- Does the fill valve keep turning on and off?
- Is the flapper sealing properly after the flush?
This quick observation will help you pinpoint the exact issue below.
Step 2: Check the Toilet Flapper
The flapper is the rubber piece at the bottom of the tank that lifts when you flush and seals the water back in once it closes.
Common Flapper Problems:
- It’s not sealing properly
- It’s warped or damaged
- The chain is too tight or too loose
Fix:
- Look at the chain connecting the flush handle to the flapper.
- If it’s too tight, the flapper won’t fully close.
- If it’s too loose, it won’t lift enough to flush properly.
- Adjust the chain so there’s about ½ inch of slack, but not so much that it gets tangled.
- Check the flapper for damage:
- If it looks warped, brittle, or cracked, replace it.
- Flappers are cheap and universal — most hardware stores sell them for under $10.
- Install the new flapper and reconnect the chain.
Flush the toilet again and see if the running stops.
Step 3: Adjust the Water Level
Sometimes the toilet runs because the water level is set too high.
If the water line is touching or above the overflow tube, it will continuously drain into the bowl.
Fix:
Locate the float inside your toilet:
- Ball Float: A plastic ball attached to a metal arm
- Cylinder Float: A modern sliding plastic cup on the fill valve
Lower the float slightly:
- Turn the adjustment screw or clip.
- For ball floats, gently bend the metal arm down.
- For cylinder floats, slide it down.
Flush again and see if the water now shuts off correctly.
Step 4: Check the Fill Valve
If the toilet still runs, your fill valve might be faulty.
The fill valve controls how water enters the tank. Over time, they wear out or get clogged with debris.
Fix:
- Turn off the water supply valve behind the toilet.
- Flush the toilet to empty the tank.
- Remove the old fill valve (usually a twist or nut underneath).
- Install a new fill valve (these are cheap and easy to replace).
- Turn the water back on and test.
Most fill valves take 10–15 minutes to replace even for first-timers.
Step 5: Test for a Slow Leak
A sneaky problem is a silent leak from the tank into the bowl.
Here’s an easy trick:
- Add a few drops of food coloring into the tank.
- Wait 15 minutes without flushing.
- If color appears in the bowl, you’ve got a leak — usually a bad flapper.
Replace the flapper and you’re good to go.
Quick Troubleshooting Chart
| Problem | Likely Cause | Solution |
|---|---|---|
| Constant running | Bad flapper | Replace flapper |
| Tank refills every few minutes | Leak into bowl | Replace flapper |
| Water spilling into overflow | Float too high | Lower float |
| Slow refill | Clogged fill valve | Replace valve |
When to Call a Plumber
Call a professional if:
- You replaced everything and it still runs
- You notice water leaking around the base
- There’s a crack in the tank or bowl
Otherwise, this is one of the most DIY-friendly plumbing fixes out there.
Final Thoughts
A running toilet might seem annoying, but it’s usually one of the easiest home plumbing problems to fix yourself.
Most repairs take under 30 minutes and cost less than $15.
Before you call a plumber or let it waste hundreds of gallons of water, go through these steps and fix it like a pro.
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