Running Toilet Won't Stop — How to Fix It

That constant sound of water running in your toilet tank isn’t just annoying — it’s literally money going down the drain. A running toilet can waste 200+ gallons of water per day. The good news: this is one of the most DIY-friendly plumbing fixes you can tackle, and it rarely takes more than 30 minutes.

What’s Actually Happening

Inside your toilet tank, a simple system controls filling and flushing. When you flush, water leaves the tank, a flapper closes to seal the bottom, and a fill valve refills the tank to a set level. When any of these parts fail, water keeps running.

The three usual suspects:

1. The flapper — the rubber seal at the tank bottom
2. The fill valve — the tall mechanism that refills the tank
3. The float — the part that tells the fill valve when to stop

Nine times out of ten, it’s one of these three. Let’s figure out which.

Quick Diagnosis: The Dye Test

Before you start taking things apart, do a simple test:

1. Remove the tank lid and set it somewhere safe (they crack easily)
2. Drop some food coloring into the tank water
3. Wait 15-20 minutes WITHOUT flushing
4. Check the bowl

If color appears in the bowl: Your flapper is leaking. Water is seeping past it into the bowl, causing the fill valve to keep refilling.

If color stays only in the tank: The problem is your fill valve or float — water is overflowing into the overflow tube.

Most Likely Causes (Ranked)

1. Bad Flapper — The #1 Culprit

The flapper is a rubber or silicone seal that covers the drain hole at the bottom of your tank. It lifts when you flush, then settles back down to seal the tank. Over time, flappers warp, crack, or get mineral buildup that prevents a good seal.

Signs it’s the flapper:

• Failed the dye test (color in bowl)
• The flapper looks warped, cracked, or has buildup
• Toilet runs intermittently (phantom flushing)
• You can stop the running by jiggling the handle

The Fix:

Flappers are universal, cheap ($5-10), and need no tools to replace.

1. Turn off the water supply valve behind the toilet (turn clockwise)
2. Flush to empty the tank
3. Unhook the old flapper from the overflow tube ears — it just snaps off
4. Disconnect the chain from the flush lever
5. Take the old flapper to the hardware store to match size and style
6. Snap the new flapper into place
7. Connect the chain with about 1/2 inch of slack
8. Turn the water back on and test

Time: 10 minutes. Cost: $5-10.

2. Float Set Too High

The float tells the fill valve when to stop filling. If it’s set too high, water rises above the overflow tube and keeps draining — which triggers more filling. It’s a feedback loop.

Signs it’s the float:

• Water is visibly going into the overflow tube (that vertical pipe in the center of the tank)
• The water level is above the line marked on the inside of the tank or overflow tube
• Passed the dye test (no color in bowl)

The Fix:

The adjustment depends on your fill valve type:

Ball float (old style — ball on an arm):

• Bend the arm slightly downward to lower the float
• Or turn the adjustment screw on the arm

Cup float (new style — float slides on the fill valve):

• Find the adjustment clip or screw on the side of the fill valve
• Slide or turn to lower the float position

The water level should be about 1 inch below the top of the overflow tube.

Time: 5 minutes. Cost: Free.

3. Faulty Fill Valve

If the flapper is fine and the float adjustment doesn’t help, the fill valve itself might be worn out. These can fail to shut off even when the float triggers them.

Signs it’s the fill valve:

• Water keeps running no matter where you set the float
• The fill valve makes strange noises (screaming, whistling)
• You’ve already replaced the flapper and adjusted the float with no luck

The Fix:

Replacing a fill valve is more involved but still DIY.

1. Turn off the water supply and flush to empty the tank
2. Place a towel under the tank and disconnect the water supply line from the bottom of the fill valve
3. Unscrew the locknut holding the fill valve to the tank (under the tank, hand-tight)
4. Remove the old fill valve
5. Adjust the new fill valve height to match your tank
6. Insert and hand-tighten the locknut
7. Connect the refill tube to the overflow pipe
8. Reconnect water supply and turn on
9. Adjust the float to proper level

Time: 20-30 minutes. Cost: $15-25 for a quality fill valve.

4. The Flush Handle Chain

Sometimes the chain connecting the handle to the flapper has issues:

• Too much slack: flapper can’t lift fully
• Too little slack: flapper can’t seat properly
• Chain tangled under flapper: prevents seal

The Fix: Adjust the chain to have about 1/2 inch of slack when the flapper is seated. Make sure nothing is caught under the flapper.

Can You Fix It Yourself?

✅ DIY-Friendly Because:

• All parts are cheap and available at any hardware store
• No special tools required — maybe a wrench
• No water damage risk — supply line has a shutoff
• Takes 30 minutes or less for most fixes
• Clear visual feedback — you can see if it’s working

🛑 Call a Pro If:

• You’re not comfortable working with plumbing
• The toilet has cracks or other damage
• The problem persists after replacing parts
• You have an unusual toilet style (wall-mount, pressure-assist)
• Water is leaking around the base (different issue — wax ring)

Step-by-Step: Complete Running Toilet Fix

Here’s the systematic approach:

Step 1: Do the dye test
Determines if it’s a flapper issue or overflow issue.

Step 2: If color in bowl → replace flapper
Most common fix. Takes 10 minutes.

Step 3: If color stays in tank → check water level
Should be 1 inch below overflow tube. Adjust float if too high.

Step 4: Still running? → Replace fill valve
Nuclear option that solves 99% of remaining cases.

What a Plumber Will Do

If you call a plumber, they’ll:

• Diagnose the issue (usually takes 5 minutes)
• Replace the necessary parts
• Test the repair

Cost: $100-200 typically, including parts and labor. It’s not that the job is hard — you’re paying for convenience and the guarantee.

Worth it if:

• Your time is more valuable
• You want a warranty on the work
• Multiple issues suggest the toilet itself is failing

Prevent Future Running Toilets

• Replace flappers proactively — every 4-5 years, or when you notice them getting stiff
• Don’t use tank tablets — those drop-in cleaners deteriorate rubber parts faster
• Check the chain occasionally — make sure it’s not kinked or binding
• Listen for phantom flushes — if you hear the toilet refill when nobody flushed, check it soon

How Much Water Is Actually Wasted?

A running toilet typically leaks 1-2 gallons per minute. That’s:

• 1,440-2,880 gallons per day
• 43,200-86,400 gallons per month
• $50-200+ added to your water bill monthly

That $10 flapper pays for itself in days.

The Bottom Line

A running toilet is almost always one of three things: flapper, float, or fill valve. You can diagnose which in 15 minutes, and fix most cases for under $25 and half an hour of your time.

Start with the flapper — it’s the culprit most of the time. Adjust the float if needed. Replace the fill valve as a last resort. If all that fails, you’ve got a weird toilet and it’s time to call a plumber (or buy a new toilet).