How to Fix a Running Toilet (Step-by-Step Guide)

A running toilet wastes up to 200 gallons of water per day and can add $50 or more to your monthly water bill. The good news: most running toilet problems are caused by a handful of cheap, easy-to-replace parts that any homeowner can fix in 15 to 30 minutes.

This guide walks you through the most common causes and step-by-step fixes. If your toilet keeps running after trying these solutions, it may be time to call a licensed plumber in Los Angeles.

Why Does a Toilet Keep Running?

A toilet runs continuously when water leaks from the tank into the bowl faster than the fill valve can refill the tank. The three most common culprits are:

1. A worn or warped flapper — the rubber seal at the bottom of the tank that lifts when you flush
2. A misadjusted float — the mechanism that tells the fill valve when to stop filling
3. A faulty fill valve — the tall assembly on the left side of the tank that controls incoming water

Tools and Parts You'll Need

• Adjustable pliers or channel locks
• Replacement flapper ($3–$8 at any hardware store)
• Replacement fill valve ($8–$15, if needed)
• Towel and small bucket

Step 1: Identify the Problem

Remove the tank lid and set it on a towel so it doesn't crack. Flush the toilet and watch what happens:

• Water keeps flowing into the bowl after the flapper closes: The flapper isn't sealing properly.
• Water rises to the top of the overflow tube and drains down it: The float is set too high, causing the tank to overfill.
• The fill valve hisses or vibrates and never fully stops: The fill valve is faulty and needs replacement.

Step 2: Fix a Worn Flapper

This is the most common cause of a running toilet, and the easiest fix.

1. Turn off the water supply by twisting the shutoff valve (usually on the wall behind the toilet) clockwise until it stops.
2. Flush the toilet to drain most of the water from the tank.
3. Remove the old flapper. Most flappers unhook from two pegs on either side of the overflow tube and disconnect from the flush chain.
4. Inspect the flapper. If it feels stiff, warped, or has visible mineral buildup, replace it. You can bring it to the hardware store to match the size.
5. Install the new flapper. Hook the ears over the pegs, reconnect the chain, and make sure there's about 1/2 inch of slack in the chain.
6. Turn the water back on and let the tank fill. The running should stop once the flapper seats properly.

Step 3: Adjust the Float

If the water level in your tank rises above the overflow tube, the float needs to be lowered. The water level should sit about 1 inch below the top of the overflow tube.

• Ball float (older toilets): Bend the metal arm slightly downward to lower the float ball, or turn the adjustment screw on top of the fill valve.
• Cup float (newer toilets): Squeeze the clip on the float cup and slide it down the fill valve shaft about half an inch.

Flush and check the water level. Repeat until water stops about 1 inch below the overflow tube.

Step 4: Replace the Fill Valve

If adjusting the float doesn't help, or if the fill valve makes a hissing or grinding noise, the whole valve needs to be replaced. Universal fill valves like the Fluidmaster 400A fit most toilets.

1. Turn off the water supply and flush to empty the tank. Sponge out remaining water.
2. Disconnect the water supply line from the bottom of the tank (have a towel ready for drips).
3. Unscrew the locknut under the tank and remove the old fill valve.
4. Adjust the height of the new fill valve so the top sits about 1 inch above the overflow tube, then insert it into the tank hole and hand-tighten the locknut.
5. Reconnect the water supply line and attach the refill tube to the overflow tube.
6. Turn on the water and check for leaks. Adjust the float to set the proper water level.

When to Call a Plumber

DIY fixes handle most running toilet issues, but call a professional if:

• The toilet continues running after replacing the flapper and fill valve
• You notice cracks in the tank or bowl
• Water is leaking from the base of the toilet
• The shutoff valve is stuck or leaking when you turn it
• Your toilet is old and you're considering a full replacement

A licensed plumber can diagnose and fix the issue quickly. In Los Angeles, a typical toilet repair runs $150–$350 depending on the problem. Browse verified plumbers in your area to compare ratings and get help fast.

How to Prevent a Running Toilet

• Replace flappers every 3–5 years — they degrade over time from chlorine and minerals in the water.
• Don't use drop-in tank tablets — the chemicals accelerate flapper deterioration.
• Check the float level annually — it takes 30 seconds and prevents water waste.
• Listen for phantom flushes — if your toilet randomly refills for a few seconds, the flapper is starting to fail.

Frequently Asked Questions

How much water does a running toilet waste?

A running toilet can waste 1 to 4 gallons per minute, which adds up to 1,400–5,700 gallons per day. Even a slow leak wastes thousands of gallons per month.

Will a running toilet increase my water bill?

Yes. A continuously running toilet can add $50–$200 or more to your monthly water bill depending on how fast it's leaking. Fixing it quickly pays for itself.

Can a running toilet fix itself?

No. A running toilet is a mechanical problem — either a worn seal, misadjusted float, or failing valve. It will get worse, not better, over time.

How much does a plumber charge to fix a running toilet?

Most plumbers charge $150–$350 for a running toilet repair, including parts. If the entire toilet needs replacement, expect $300–$600 installed. See our complete plumber cost guide for more details.