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

A running toilet wastes up to 200 gallons a day — that's $70+/month at LA water rates. In most cases a $5 fix takes 10 minutes. Here's how to do it.

Step 1: Diagnose the Cause (2 minutes)

Remove the tank lid and watch what's happening:

• Water spilling into the overflow tube (the tall tube in the center) → The float is set too high. Go to Step 3.
• Water level below the overflow tube, but toilet runs or phantom-flushes → Do the food dye test: Add several drops of food coloring to the tank. Wait 10 minutes without flushing. If color appears in the bowl, your flapper is leaking. Go to Step 2.
• Fill valve constantly cycling on and off → The fill valve may be faulty. Go to Step 4.

Step 2: Replace the Flapper (Most Common Fix)

What you need: Replacement flapper ($5–$15, sold at any hardware store — bring your toilet's model number or the old flapper to match it) and a towel.

1. Turn off the supply valve — the oval knob on the wall behind the toilet. Turn clockwise until it stops.
2. Flush to drain the tank. Sponge out any remaining water.
3. Unhook the chain from the flush handle arm.
4. Slide the flapper off the overflow tube pegs (it either unclips or slides off the side ears).
5. Snap the new flapper onto the pegs. Hook the chain to the flush handle arm with about 1/2 inch of slack (not too tight, not too loose).
6. Turn the supply valve back on. Let the tank fill. Test the flush. Check for color in the bowl after 10 minutes.

Step 3: Adjust the Float (If Water Overflows Into the Overflow Tube)

The water level should sit about 1 inch below the top of the overflow tube. To lower it:

• Ball float (older toilets): The float is a ball on an arm. Gently bend the arm slightly downward, or turn the adjustment screw at the valve where the arm connects.
• Cup float (newer toilets): The float is a plastic cylinder on the fill valve shaft. Pinch the clip on the side and slide the float down. Clockwise lowers it on some models.

Step 4: Replace the Fill Valve (If Still Running)

If the fill valve constantly cycles or never fully shuts off, replace it. A Fluidmaster 400A ($10–$15) fits most toilets universally.

1. Shut off supply valve. Flush and sponge out the tank.
2. Disconnect the supply line from the bottom of the tank.
3. Unscrew the large locknut from underneath the tank (counterclockwise).
4. Pull out the old fill valve. Drop in the new one. Hand-tighten the locknut — don't overtighten or the tank will crack.
5. Reconnect the supply line. Turn water on slowly. Set the water level per the instructions (typically the float clip adjustment).
6. Check that the refill tube is aimed into the overflow tube (not the bottom of the tank).

When to Call a Plumber Instead

Call a licensed plumber if:

• The supply shutoff valve won't close — it's corroded or stuck. Turning it further could break the pipe.
• The tank or bowl is cracked — requires full toilet replacement.
• Water is leaking around the base of the toilet — wax ring issue, requires lifting the toilet.
• You've replaced the flapper and fill valve and it's still running — there may be a crack in the overflow tube or flush valve seat that requires more diagnosis.

A plumber in Los Angeles charges $125–$300 to repair or replace a toilet. Full toilet replacement (supply, labor, new toilet) runs $350–$700.

Frequently Asked Questions