Quick Answer
90% of running toilets are caused by a worn flapper ($5–$10 fix) or a float set too high (free fix). Add food coloring to the tank — if it appears in the bowl without flushing, replace the flapper. If water spills into the overflow tube, lower the float. Both fixes take under 20 minutes with no plumbing experience.
Step 1: Diagnose the Problem First
Remove the tank lid and look inside. There are only three things that cause a running toilet:
Food Coloring Test (takes 15 min):
- 1. Drop 5–10 drops of food coloring into the tank (not the bowl).
- 2. Wait 15 minutes without flushing.
- 3. Color in bowl = flapper is leaking. No color = check float/overflow tube.
AReplace the Flapper (Most Common Fix)
The flapper is the rubber seal at the bottom of the tank. It costs $5–$10 and takes 10 minutes to replace.
- 1. Turn the shutoff valve behind/below the toilet clockwise until it stops.
- 2. Flush to drain the tank. Wipe up remaining water with a sponge.
- 3. Unhook the flapper ears from the two side pegs on the overflow tube.
- 4. Detach the chain from the flush handle arm.
- 5. Take the old flapper to the hardware store for an exact match (or buy a universal flapper).
- 6. Hook the new flapper on the pegs and attach the chain — leave about ½ inch of slack.
- 7. Turn the water back on. Let the tank fill. Flush and watch: the flapper should drop and seal fully.
BAdjust the Float (If Water Is Above the Overflow Tube)
The water level should sit about 1 inch below the top of the overflow tube (the tall hollow tube in the center of the tank). If it's higher, water continuously spills into the bowl.
Older ball-float style:
The float is a hollow ball on the end of a metal arm. Gently bend the arm downward so the ball floats lower and the fill valve shuts off sooner.
Modern cup-float style (most common now):
Find the adjustment screw or pinch clip on the fill valve shaft. Turn the screw counterclockwise to lower the water level, or pinch the clip and slide it down. Target: 1 inch below the overflow tube top.
CReplace the Fill Valve (If Adjustments Don't Help)
A Fluidmaster 400A or similar universal fill valve costs $10–$20 and fits virtually every toilet. This is a 20-minute job.
- 1. Turn off the shutoff valve and flush to empty the tank.
- 2. Disconnect the water supply line from the bottom of the tank.
- 3. Unscrew the large plastic locknut under the tank (counterclockwise by hand or with pliers).
- 4. Pull out the old fill valve from inside the tank.
- 5. Adjust the new fill valve's height so its top is about 1 inch above the overflow tube.
- 6. Insert it through the tank hole, tighten the locknut underneath (hand-tight + ¼ turn).
- 7. Connect the refill tube to the overflow tube. Reconnect the supply line. Turn water on slowly.
Call a Plumber When...
- You replaced the flapper and fill valve and it still runs
- The shutoff valve under the toilet is stuck or leaking
- Water is leaking at the base of the toilet (wax ring issue)
- The toilet tank is cracked
Plumber cost to fix a running toilet: $75–$175 including parts.
Frequently Asked Questions
How do I fix a running toilet without calling a plumber?
A running toilet is almost always caused by a worn flapper, faulty fill valve, or float set too high. Lift the tank lid and press the flapper — if the running stops, replace the flapper ($5–$10 at any hardware store). If the water level is above the overflow tube, adjust the float downward. Most running toilet repairs take under 30 minutes and require no tools.
Why does my toilet keep running after I flush?
The three most common causes are: (1) A worn or warped flapper that no longer seals the hole between the tank and bowl — water slowly leaks through. (2) The float is set too high, so the water level rises above the overflow tube and drains into the bowl constantly. (3) A faulty fill valve that cannot shut off water flow. You can diagnose which one by adding food coloring to the tank: if it appears in the bowl without flushing, it is the flapper.
How much water does a running toilet waste?
A running toilet typically wastes 200 to 400 gallons of water per day, depending on severity. That is roughly $50 to $100 per month added to your water bill. A silent leak (water seeping slowly through a worn flapper) can waste 30 to 500 gallons per day and often goes undetected for months.
How much does a toilet flapper cost?
A replacement toilet flapper costs $5 to $15 at any hardware store. Universal flappers fit most toilets, but some brands require specific flappers — bring the old one to the store for matching. A fill valve replacement costs $10 to $20. A plumber charges $75 to $175 to diagnose and fix a running toilet including parts.
My toilet runs for a few seconds then stops — what is wrong?
This is called "phantom flushing" or intermittent running, and it almost always means the flapper has a slow leak. Water silently drains from the tank into the bowl until the tank level drops enough to trigger the fill valve. The fill valve refills the tank for a few seconds, then shuts off — and the cycle repeats. Replace the flapper to fix this.
Still Running? Find a Plumber Near You
Compare reviews from real customers. Find a licensed plumber in your area fast.
Find a Plumber