Toilet Running Constantly
A toilet that runs constantly is wasting 200+ gallons of water per day... that's $30-$50/month on your water bill. The good news is that this is almost always a $5-$15 fix you can do yourself in 10 minutes with no tools beyond your hands. The running sound means water is flowing from the tank into the bowl when it shouldn't be.
What to Check Before You Call Someone
Jiggle the flush handle
Sometimes the flapper chain gets caught under the flapper or the handle sticks in the down position, holding the flapper open. A quick jiggle frees it.
Fix: If jiggling stops the running, the chain length is probably wrong. Adjust the chain so there's about 1/2 inch of slack when the flapper is closed. Too much slack = weak flush. Too little = the chain holds the flapper open.
Check the flapper
Lift the tank lid and look at the rubber flapper at the bottom of the tank. Press down on it with your finger. If the running stops when you press the flapper down, the flapper isn't sealing properly.
Fix: Flappers warp and deteriorate over time (2-5 years). Replace it: turn off the water supply valve behind the toilet, flush to drain the tank, unhook the old flapper from the overflow tube ears, and snap the new one on. A Korky or Fluidmaster universal flapper is $5-$8 at any hardware store. This fixes running toilets about 80% of the time.
Check the water level
The water level in the tank should be about 1 inch below the top of the overflow tube (the tall vertical pipe in the center of the tank). If water is flowing INTO the overflow tube, the tank is overfilling.
Fix: Adjust the fill valve float. On a ball float (older style), bend the metal arm down slightly to lower the water level. On a modern fill valve with an adjustment screw, turn the screw clockwise to lower the water level. The goal is water stopping about 1 inch below the overflow tube top.
Check the fill valve for constant running
If the water level is correct (below the overflow) but the fill valve keeps running or cycles on and off, the fill valve itself is worn out. Debris or mineral buildup inside the valve can prevent it from shutting off completely.
Fix: Try cleaning the fill valve first: turn off the water, remove the cap on top of the fill valve (usually twists off), rinse it under the faucet to remove debris, and reinstall. If it still runs, replace the entire fill valve... a Fluidmaster 400A is $8-$12 and takes 15 minutes to install. Turn off water, flush, disconnect supply line, unscrew old valve, install new valve, reconnect.
Check the overflow tube height
If the overflow tube is cracked or too short, water drains into the bowl constantly. This is less common than a flapper or fill valve issue, but it happens.
Fix: If the overflow tube is cracked, the entire flush valve assembly needs replacement ($15-$25 for the part). This is a bigger job... the tank needs to come off the bowl. It's still DIY-able (30-45 minutes) but if you're not comfortable, a plumber charges $100-$200.
When It's Time to Replace
A running toilet almost never means you need a new toilet. The internal parts (flapper, fill valve, flush valve) are all replaceable for $5-$25 each. The toilet itself (the porcelain bowl and tank) lasts 25-50 years. Replace the toilet only if the porcelain is cracked, it's an old water-wasting model (pre-1994 toilets use 3.5-7 gallons per flush vs 1.28-1.6 for modern toilets), or you want to upgrade for other reasons.
Read our full Toilet replacement guide →When to Call a Professional
This is one of the most DIY-friendly repairs in your home. Call a plumber only if: you've replaced the flapper and fill valve and it still runs (the flush valve assembly may need replacement, which requires removing the tank), if there's water leaking from the base of the toilet (that's a wax ring issue, not a running issue), or if you simply don't want to deal with it. A plumber charges $100-$200 for what's usually a $10 part and 15 minutes of work.
This guide is for informational purposes. For gas leaks, electrical issues, or emergencies, call a licensed professional immediately.