How to Fix a Running Toilet

Difficulty: Easy • Time: 20 min active, 30 min total • Estimated cost: $8-25 • Safety: DIY-friendly

Overview

A running toilet is one of the most common — and most annoying — household problems. That constant sound of water flowing means your toilet is continuously refilling, wasting up to 200 gallons of water per day and adding $50+ to your monthly water bill.

The good news? In 90% of cases, the fix takes less than 20 minutes and costs under $25. The three most common causes are a worn flapper (the rubber seal at the bottom of the tank), a faulty fill valve, or an improperly adjusted float. We'll walk you through diagnosing which one it is and fixing it.

No special skills required — if you can turn a wrench and flush a toilet, you can do this repair.

Tools Needed

Adjustable wrench
Towel or sponge
Bucket
Rubber gloves (optional)

Materials Needed

Universal toilet flapper — $5-8
Toilet fill valve (if needed) — $8-15
Toilet repair kit (covers everything) — $15-25

Step-by-Step Instructions

Diagnose the problem: Remove the tank lid and set it aside carefully (porcelain breaks easily). Look inside while the toilet runs. If water is flowing over the overflow tube, your float is set too high. If water is leaking from the bottom of the tank into the bowl, your flapper is worn. Drop a few drops of food coloring into the tank water — if color appears in the bowl without flushing, the flapper is definitely leaking.
Turn off the water supply: Locate the shut-off valve behind the toilet, near the floor. Turn it clockwise until it stops. Flush the toilet to drain most of the tank water. Use a towel or sponge to soak up any remaining water in the tank. This gives you a dry workspace.
Replace the flapper (most common fix): Unhook the old flapper from the overflow tube ears — it usually just unclips. Disconnect the chain from the flush lever. Take the old flapper to the hardware store if you're unsure of the size, or use a universal flapper. Hook the new flapper onto the overflow tube ears, reconnect the chain to the flush lever with about 1/2 inch of slack. Too much slack and it won't seal; too little and it won't close fully.
Adjust the float (if water is too high): If water is running over the overflow tube, you need to lower the float. For a ball float (the big ball on an arm), bend the arm slightly downward or turn the adjustment screw on top. For a cylinder float (slides up and down the fill valve), pinch the spring clip and slide the float down about 1 inch. The water level should sit about 1 inch below the top of the overflow tube.
Replace the fill valve (if still running): If a new flapper and float adjustment don't fix it, the fill valve itself may be worn. Disconnect the water supply line from the bottom of the tank (have a bucket ready for drips). Unscrew the locknut holding the fill valve in place. Remove the old valve and insert the new one, adjusting the height to match the overflow tube. Tighten the locknut by hand plus 1/2 turn with a wrench. Reconnect the water supply line.
Turn water back on and test: Slowly turn the shut-off valve counter-clockwise to restore water. Let the tank fill completely. Flush 2-3 times and listen — the running sound should be gone. Check that water stops filling about 1 inch below the overflow tube. Do the food coloring test again to confirm the flapper is sealing properly. Replace the tank lid.

When to Call a Professional

Call a plumber if the toilet is cracked, leaking from the base (wax ring issue), if you see water damage on the ceiling below a second-floor bathroom, or if the shut-off valve is stuck or leaking when you try to turn it.