Stop a Constantly Running Toilet

Category: Plumbing · Difficulty: Beginner · Time: 1.5h · Estimated cost: $25

Tools needed

Diagnose
Lift the tank lid. If water trickles into the bowl constantly, the flapper is leaking. If water rises past the overflow tube and runs down it, the fill valve or float is set wrong.
Duration: 5 min
Shut water and drain tank
Close the supply valve behind the toilet. Flush to empty the tank. Sponge out remaining water.
Duration: 10 min
Replace flapper
Unhook the chain from the flush lever, slide the old flapper off the overflow tube ears. Slide new flapper on, hook chain with about 1/2" slack.
Duration: 10 min
Replace fill valve (if needed)
From under the tank, unscrew the supply line and the lock nut. Lift the old fill valve out from above. Insert new valve, tighten lock nut from below, reconnect supply.
Duration: 25 min
Set water level
Open shutoff slowly. Adjust float screw so water stops 1" below the top of the overflow tube.
Duration: 10 min
Test for 30 minutes
Listen for any refill cycles. If silent for 30 min, the leak is fixed.
Duration: 30 min

Always shut off the supply valve before working — pressurized water sprays surprisingly far.
Don't overtighten plastic nuts on the fill valve; they crack.

If the tank itself is cracked, or you see brown water around the base, you need a plumber for the flange or tank.