If your toilet keeps running long after you flush — or seems to turn on and off by itself — it can be annoying and expensive. A running toilet can waste hundreds of gallons of water a day if left unchecked.
In most cases, the problem is caused by a simple issue inside the toilet tank.
Quick Answer:
A toilet usually won’t stop running because water is leaking from the tank into the bowl due to a faulty flapper, improperly adjusted float, or a fill valve that isn’t shutting off correctly. Fixing or adjusting these parts usually stops the running immediately.
Why This Happens
Toilets rely on a balance of parts inside the tank to stop water flow once the tank refills. When one of those parts fails or moves out of position, water continues to flow.
The most common causes are:
- A worn or misaligned flapper
- A float set too high or too low
- A fill valve that doesn’t shut off properly
- A loose or tangled lift chain
These issues are mechanical and usually develop gradually, even if the toilet worked fine recently.
Step-by-Step: How to Fix a Toilet That Won’t Stop Running
Step 1: Remove the Tank Lid and Observe
Take off the toilet tank lid and look inside while the toilet is running.
Watch for:
- Water flowing into the overflow tube
- The flapper not sealing fully
- The float sitting too high
This visual check usually reveals the issue quickly.
Step 2: Check the Flapper
Look at the rubber flapper at the bottom of the tank.
Make sure:
- It lies flat over the flush valve opening
- It isn’t warped, cracked, or stiff
- The chain has slight slack and isn’t tangled
A flapper that doesn’t seal properly allows water to leak continuously into the bowl.
Step 3: Adjust the Float
If water is flowing into the overflow tube, the float is set too high.
Depending on your toilet:
- Turn the adjustment screw on the fill valve
- Slide the float down slightly
- Lower the float cup on modern fill valves
The water level should sit about one inch below the top of the overflow tube.
Step 4: Test the Fill Valve
Flush the toilet and watch how the tank refills.
If the fill valve continues running after the tank is full, it may be worn or clogged with debris. Lightly tapping it sometimes helps temporarily, but replacement is often the permanent fix.
Step 5: Flush and Recheck
Flush the toilet once more and confirm that:
- The tank fills
- Water shuts off
- No water continues flowing into the bowl
Most fixes work immediately.
What Not to Do
- Don’t ignore a constantly running toilet
- Don’t overtighten internal parts
- Don’t assume the toilet needs to be replaced
- Don’t pour chemicals into the tank
Running toilets are usually simple mechanical issues, not major failures.
When to Call a Professional
Call a plumber if:
- The toilet continues running after replacing parts
- Water leaks onto the floor
- The flush valve seat is damaged
- Multiple toilets show similar issues
These cases may indicate a deeper plumbing or pressure-related problem.
Safety Notes
- Turn off the toilet supply valve if you need to stop water temporarily
- Use caution when handling porcelain parts
- Keep the tank lid secure to avoid cracks
- Dry the area around the toilet to spot leaks easily
Common Homeowner Questions
Is a running toilet expensive?
Yes. A running toilet can waste hundreds of gallons of water per day.
Can this cause damage?
It usually won’t cause immediate damage, but it increases water bills and can stress internal parts.
How long does the fix take?
Most fixes take 5–15 minutes once the issue is identified.