A running toilet. Nearly always the flapper. A DIY job for most people.
Nothing floods, but the EPA says a leaking toilet can waste thousands of gallons a year and it shows on the water bill.
What is probably happening
- The flapper (the rubber disc at the bottom of the tank) is worn and lets water seep into the bowl, so the tank keeps refilling.
- The float is set too high and water runs into the overflow tube.
- The fill valve is worn and does not shut off.
Do this in the next five minutes
- Lift the tank lid. If water is trickling into the overflow tube, lower the float.
- EPA WaterSense test: put a few drops of food coloring in the tank. If color shows in the bowl after 10 minutes without flushing, the flapper leaks.
- Turn off the valve behind the toilet, flush to empty the tank, unhook the old flapper and take it to the hardware store to match.
- Fit the new flapper, turn the water back on, flush twice and watch it stop.
- If it still runs, the fill valve is next. Also a hardware store part, or a plumber.
Do not
- Do not put bleach tablets in the tank. They eat rubber flappers and cause exactly this.
- Do not pay an emergency rate for a running toilet. It waits for a weekday.
- Do not accept a new toilet quote for a flapper problem.
Who to call
A licensed plumber, if you would rather not do it
Honest answer: a flapper is a ten minute, under $20 job most homeowners can do. A plumber is for a fill valve you cannot match, or a toilet you cannot get parts for.
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What it should cost
$100 to $400
Plumber repairing a running toilet, national range. Fill valve replacement $50 to $150
Source: Angi, toilet repair cost, updated July 2026. View source
National published range, not a quote for your job. The full cost table for this trade is on the plumbing page.
Ask this contractor, on the phone, before anyone comes out
Tap each one as you ask it.
- Is it the flapper, the float or the fill valve, and which are you replacing?
- Is this a standard rate visit, and is the trip fee applied to the repair?
- Can you do the other toilets while you are here, and at what price each?
End the call if
- A replacement toilet quoted for a running tank.
- An emergency premium for a non emergency.
- A plumber who does not do the food coloring test or look inside the tank.