How to Stop a Toilet from Running (Step-by-Step)

Scope of this guide: This page is the troubleshooting guide: it helps identify the failed toilet component and decide whether to repair it. For contractor pricing, use the linked cost guide.

A running toilet is one of the easiest home repairs you can do yourself. The parts cost $10-$25 at any hardware store, and the whole job takes 30-45 minutes. This guide walks you through diagnosing and fixing the three most common causes.

Diagnosing the Problem First

Before buying parts, figure out what's wrong. Lift the tank lid (the flat lid on the back of the toilet, not the seat) and look inside. The toilet has two main components:

The fill valve: The mechanism on the left side that fills the tank with water after flushing. When it's working correctly, water fills to a set level and then stops.

The flapper: The rubber disk or cone at the bottom of the tank that opens during flushing and seals shut as the tank refills. If it doesn't seal properly, water continuously leaks into the bowl.

The overflow tube: The large tube in the center of the tank. Water level should be about 1 inch below the top of this tube. If water is spilling into it, the fill valve isn't shutting off.

Cause 1: The Flapper Is Leaking (Most Common)

Test: Put a few drops of food coloring in the tank. Wait 15 minutes without flushing. If colored water appears in the bowl, the flapper is leaking.

Symptoms: Toilet occasionally fills briefly and stops (phantom flushing), or there's a constant subtle sound of running water.

How to fix:

1. Turn off the water supply valve (the knob or handle behind and below the toilet)
2. Flush to empty the tank
3. Note how the existing flapper is attached: most clip onto two pegs on the sides of the overflow tube, or have a ring that slips over the tube
4. Disconnect the chain from the flush handle arm
5. Remove the old flapper (unclip or slip off)
6. Bring the old flapper to the hardware store to match it, OR buy a universal replacement (most common size fits most toilets)
7. Install the new flapper by clipping it onto the pegs
8. Reconnect the chain - leave about 1/2 inch of slack. Too tight = flapper won't seal. Too loose = gets caught under the flapper
9. Turn the water supply back on
10. Flush several times and observe - the tank should fill and stop

Cost: $5-$15 for the flapper.

Cause 2: The Fill Valve Is Failing

Symptoms: Toilet runs continuously with a hissing sound from the fill valve. Water level in the tank may be at the correct level but the valve doesn't shut off.

Test: Look at the water level in the tank. If it's below the top of the overflow tube but the toilet is still running, the fill valve isn't shutting off properly.

How to fix:

1. Turn off the water supply valve
2. Flush to empty the tank
3. Disconnect the water supply line from the bottom of the fill valve (have a bucket ready)
4. Remove the old fill valve (turn counterclockwise and lift out)
5. Install a new fill valve according to package instructions (Fluidmaster 400A is the standard replacement for most toilets)
6. Reconnect the supply line and refill tube
7. Turn the water back on
8. Set the water level: adjust the fill valve height or float adjustment so water level sits about 1 inch below the top of the overflow tube
9. Flush and confirm the valve fills and stops correctly

Cost: $10-$20 for a fill valve (Fluidmaster 400A is about $15).

Cause 3: Float Is Set Too High

Symptoms: Water is running over the top of the overflow tube into the bowl. You can hear it and see the water level is at or above the tube top.

Test: Lift the float arm (older ballcock style) or look for the float cup on newer fill valves. If water level is at or above the overflow tube, the float is set too high.

How to fix:

• Older ballcock style: Bend the float arm slightly downward, or adjust the adjustment screw if one exists
• Newer style (like Fluidmaster): Adjust the float adjustment screw or slide the float cup down the fill valve stem

The goal: water level 1 inch below the top of the overflow tube.

Cost: Free - just an adjustment.

When to Call a Plumber

Call a plumber when: - You've replaced the fill valve and flapper and the toilet still runs - The shutoff valve behind the toilet is stuck and won't turn - You hear water running but the tank looks dry (possible leak in the wax ring or bowl) - The toilet rocks when you sit on it (separate issue - wax ring)

Total DIY Cost Breakdown

Flapper only: $5-$15 Fill valve only: $10-$20 Both together (recommended): $15-$30

A "toilet repair kit" with both components and a new handle is $20-$30 and is the practical choice if the toilet is more than 5 years old.

Bottom Line

A running toilet is a $10-$30 DIY repair in most cases. The fix is a flapper replacement, a fill valve replacement, or a float adjustment. The water savings alone (200-400 gallons/day) justify doing it immediately rather than waiting.

Sources and editorial notes

Prices and permit requirements vary by location, property, equipment, and scope. Treat price ranges as planning estimates and confirm current requirements with the relevant authority and contractor.

• US Consumer Product Safety Commission - home safety

Related guides

• How Much Does It Cost to Fix a Running Toilet?
• Toilet Replacement Cost: Supply, Labor, and What to Watch For
• How to Replace a Toilet Flapper (Step-by-Step)

Next step

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