How to Fix a Running Toilet in 15 Minutes

A running toilet is one of the most common and most wasteful household problems. Left unfixed, it can waste 200 gallons of water per day and add $50 or more to your monthly water bill. The good news: you can fix almost every running toilet yourself in 15 minutes with basic tools and a $10-20 repair kit.

What Causes a Toilet to Run?

There are three main culprits. You can diagnose which one you have in under a minute.

1. Worn Flapper Valve (Most Common)

The flapper is the rubber seal at the bottom of your tank. Over time, it warps, cracks, or builds up mineral deposits, letting water constantly leak from the tank into the bowl.

How to check: Drop a few drops of food coloring into the tank. Wait 10 minutes without flushing. If the colored water appears in the bowl, your flapper is leaking.

How to fix:

1. Turn off the water supply valve behind the toilet (turn clockwise).
2. Flush to empty the tank.
3. Unhook the old flapper from the overflow tube ears and disconnect the chain from the flush lever.
4. Take the old flapper to the hardware store to match the size, or buy a universal flapper kit.
5. Install the new flapper by hooking it onto the overflow tube ears.
6. Connect the chain to the flush lever, leaving about 1/2 inch of slack.
7. Turn the water back on and test.

Cost: $5-8 for a universal flapper.

2. Float Set Too High

If the water level in your tank is above the overflow tube, water constantly drains into it. This means your float is set too high.

How to check: Look inside the tank. If water is flowing into the overflow tube, the float needs adjusting.

How to fix:

• Ball float (older toilets): Bend the metal arm slightly downward so the ball sits lower.
• Cup float (newer toilets): Pinch the clip on the float and slide it down the rod about 1/2 inch. Test and adjust until water stops about 1 inch below the top of the overflow tube.

Cost: Free (adjustment only).

3. Faulty Fill Valve

If the fill valve hisses or runs continuously even after adjusting the float, the valve itself may be worn out.

How to fix:

1. Turn off the water supply and flush to empty the tank.
2. Place a towel under the supply line connection.
3. Disconnect the supply line from the bottom of the fill valve.
4. Unscrew the lock nut holding the fill valve in place.
5. Remove the old valve and insert the new one, adjusting height to match the overflow tube.
6. Hand-tighten the lock nut, reconnect the supply line, and turn the water on.
7. Adjust the float to set the proper water level.

Cost: $8-15 for a universal fill valve kit.

Tools You Need

• Adjustable pliers or wrench
• Towel or sponge
• Replacement parts (flapper, fill valve, or both)

Most hardware stores sell complete toilet repair kits that include both a flapper and fill valve for $15-20. If your toilet is more than 5 years old, replacing both at once saves a second trip.

When to Call a Plumber

Call a professional if:

• The toilet rocks or is loose at the base (the wax ring may need replacing — see our guide on how to install a toilet if it needs a full replacement)
• You see water damage on the ceiling below the bathroom
• The porcelain is cracked
• You have replaced the flapper and fill valve but the toilet still runs

A plumber typically charges $150-300 for a toilet repair visit.

Bottom Line

A running toilet is almost always a $10 fix you can do in 15 minutes. Start with the food coloring test to check the flapper, then check the float height. These two fixes solve 90% of running toilet problems. Save yourself $200+ on a plumber and stop wasting water today.

Add this to your annual home maintenance schedule so you catch toilet issues before they waste hundreds of gallons. And while you are working in the bathroom, it is a good time to check your drains — here is how to unclog a drain without chemicals.