How to Fix a Running Toilet
A running toilet is usually caused by a worn flapper, a faulty fill valve, or an improperly adjusted float. Most fixes take 15–30 minutes and cost $5–$25 in parts. Replace the flapper first — it solves the problem 80% of the time.
Cost Breakdown
| Service | Low | High | Notes |
|---|---|---|---|
| Flapper replacement (DIY) | $5 | $10 | 10-minute fix |
| Fill valve replacement (DIY) | $10 | $20 | 30-minute fix |
| Complete rebuild kit (DIY) | $15 | $30 | Flapper + fill valve + handle |
| Professional repair | $100 | $200 | If you prefer to hire out |
How to Fix a Running Toilet (Step-by-Step Guide)
A running toilet is more than just an annoying sound — it can waste over 200 gallons of water per day, adding $50–$100 per month to your water bill. That's up to $1,200 per year wasted on a problem that usually costs less than $25 to fix. The good news: most running toilet repairs are simple DIY projects that any homeowner can tackle with basic tools and 15–30 minutes of time.
Diagnose the Problem First
Before buying parts, identify which component is causing the issue. Remove the tank lid and observe what's happening inside while the toilet runs. There are three main culprits, and a simple test can identify which one you're dealing with.
The Food Coloring Test
Add 5–10 drops of food coloring to the tank water (don't flush). Wait 15 minutes. If colored water appears in the bowl, the flapper is leaking — this is the cause about 80% of the time. If the water in the bowl stays clear, the issue is likely the fill valve or float adjustment.
Common Causes and Costs
| Cause | DIY Parts Cost | Professional Cost | DIY Difficulty |
|---|---|---|---|
| Worn flapper | $5–$10 | $125–$200 | Easy (5 min) |
| Faulty fill valve | $10–$25 | $150–$250 | Easy-Moderate (20 min) |
| Float set too high | $0 (adjustment) | $100–$175 | Easy (2 min) |
| Overflow tube crack | $15–$30 | $150–$275 | Moderate (30 min) |
| Corroded flush valve seat | $5–$15 (seat repair kit) | $150–$250 | Moderate (20 min) |
| Cracked tank or bowl | $150–$400 (new toilet) | $300–$600 installed | Replace needed |
Fix #1: Replace the Flapper (Most Common Fix)
The flapper is the rubber seal at the bottom of the tank that lifts when you flush and reseals to hold water. Over time, the rubber deteriorates, warps, or develops mineral buildup, preventing a watertight seal. Replacing it is the single most common toilet repair.
Step 1: Turn Off the Water Supply
Locate the shut-off valve on the wall behind the toilet (usually on the lower left). Turn it clockwise until it stops. Flush the toilet to empty most of the water from the tank.
Step 2: Remove the Old Flapper
Unhook the flapper ears from the pegs on either side of the overflow tube. Disconnect the chain from the flush lever arm. Inspect the old flapper — if it's warped, crumbly, or stained with mineral deposits, replacement is the right call.
Step 3: Buy the Right Replacement
Take the old flapper to the hardware store to match the size and style. Universal flappers ($5–$8) work for most toilets, but some brands like Kohler and American Standard use proprietary sizes. The packaging will list compatible toilet brands and models.
Step 4: Install the New Flapper
Hook the new flapper ears onto the overflow tube pegs. Connect the chain to the flush lever arm, leaving approximately 1/2 inch of slack in the chain. Too much slack prevents a complete flush; too little prevents the flapper from sealing properly after flushing.
Step 5: Turn On Water and Test
Turn the supply valve back on counterclockwise. Let the tank fill completely. Flush twice and listen — the running sound should be gone. Repeat the food coloring test to confirm the seal is watertight.
Fix #2: Adjust the Float
If the water level in the tank is too high, it flows continuously into the overflow tube, causing the toilet to run. The fix is simply lowering the float so the fill valve shuts off at the correct water level (usually marked with a line inside the tank, about 1 inch below the overflow tube).
For a ball float (older toilets), bend the float arm slightly downward, or turn the adjustment screw at the top of the fill valve. For a cup float (most modern toilets), pinch the clip on the float and slide it down the fill valve shaft about 1/2 inch at a time. Test after each adjustment until the water stops at the correct level.
Fix #3: Replace the Fill Valve
If the flapper is fine and the float adjustment doesn't help, the fill valve itself may be worn out and needs replacement. This is a slightly more involved repair but still very doable as a DIY project.
Step 1: Drain the Tank Completely
Turn off water, flush, and use a sponge or towel to remove any remaining water in the tank bottom.
Step 2: Disconnect the Water Supply
Place a towel under the tank. Disconnect the water supply line from the bottom of the fill valve using an adjustable wrench or pliers.
Step 3: Remove the Old Fill Valve
Unscrew the lock nut on the outside bottom of the tank that holds the fill valve in place. Lift the old valve out from inside the tank.
Step 4: Install the New Fill Valve
Insert the new fill valve (Fluidmaster 400A is the most popular universal option; Kohler also makes excellent replacement valves). Adjust its height so the top sits about 1 inch above the overflow tube. Tighten the lock nut hand-tight plus a quarter turn with pliers — don't overtighten or you'll crack the tank.
Step 5: Reconnect and Test
Reconnect the water supply line, turn on the water, and watch the tank fill. Adjust the float to set the water level to the marked line inside the tank. Flush several times to confirm everything works correctly.
DIY vs. Calling a Plumber
Fixing a running toilet is one of the best DIY plumbing projects for beginners — you'll save $100–$250 in labor costs, learn a useful skill, and fix the problem in under 30 minutes in most cases. However, call a professional if you notice cracks in the tank or bowl, water leaking onto the floor around the toilet base, the problem persists after replacing both the flapper and fill valve, or you're uncomfortable working with the plumbing. Find a licensed plumber near you if DIY methods aren't resolving the problem.
Frequently Asked Questions
Why does my toilet run intermittently (ghost flushing)?
Intermittent running, sometimes called "ghost flushing" or "phantom flushing," is almost always caused by a slow flapper leak. The tank gradually loses water through the leaky flapper seal. When the water level drops enough, the fill valve activates to refill the tank, creating the phantom flush sound. Replacing the flapper (a 5-minute, $5–$10 fix) eliminates ghost flushing in nearly every case.
How much water does a running toilet waste?
A continuously running toilet can waste 200+ gallons per day — that's over 6,000 gallons per month or 72,000 gallons per year. In dollar terms, that adds $50–$100+ per month to your water bill depending on local water rates. A $5 flapper replacement can save you $600–$1,200 per year, making it one of the highest-ROI home repairs you can make.
Can a running toilet increase my water bill?
Yes, dramatically. Even a slow, silent leak can waste 30–50 gallons per day and add $15–$30/month to your bill. A fully running toilet is much worse. If you've noticed an unexplained spike in your water bill, check your toilets first — they're the most common source of hidden water waste in homes.
Should I replace or repair an old toilet?
If your toilet is over 15 years old and needs frequent repairs, replacing it with a modern low-flow model from Kohler, Delta, or American Standard makes financial sense. New toilets use 1.28 gallons per flush (vs. 3.5–7 gallons for pre-1994 models), saving hundreds of gallons per month. New toilets cost $150–$500 for the unit plus $150–$300 for professional installation.
What tools do I need to fix a running toilet?
Most running toilet repairs require only an adjustable wrench or pliers, a flathead screwdriver, and the replacement part (flapper or fill valve). No special plumbing tools are needed. Total tool investment for a first-timer is under $20, and you'll use these tools for many future home repairs.
Related Questions
How much water does a running toilet waste?
A constantly running toilet can waste 200 gallons per day — that is 6,000 gallons per month. Even a slow leak wastes 30–50 gallons daily. Fixing it immediately saves $30–$100+ per month on your water bill.
Can a running toilet increase my water bill?
Yes, significantly. A running toilet can add $30–$100 per month to your water bill depending on the severity of the leak. It is one of the most common causes of unexpectedly high water bills.
How do I know if my toilet flapper needs replacing?
Drop a few drops of food coloring into the tank (not the bowl). Wait 15 minutes without flushing. If color appears in the bowl, the flapper is leaking and needs replacement. Most flappers last 3–5 years.