How to Fix a Toilet That Keeps Running

If your toilet keeps running after flushing — or runs on and off randomly — it's wasting water and money every day. Here's how to pinpoint the cause and fix it fast.

Diagnose It in 60 Seconds

Take the lid off the tank and observe:

Water flowing into the overflow tube (the tall center tube) — the fill valve isn't shutting off, or the float is set too high
Water level is fine but toilet still runs — the flapper isn't sealing, water is slowly leaking into the bowl
Toilet runs for 30–60 seconds after flushing then stops — normal refill cycle. If it runs longer, something is wrong.

Quick flapper test: Press down on the flapper with your finger. If the running stops immediately, the flapper is the problem.

Quick fill valve test: Lift the float arm up. If the running stops, the float is set too high — adjust or replace the fill valve.

Fix 1: Replace the Flapper

👉 Universal toilet flapper

Turn off the water supply valve (clockwise)
Flush to empty the tank
Unhook the old flapper from the overflow tube ears and disconnect the chain
Snap the new flapper onto the ears and reconnect the chain with ½ inch of slack
Turn water back on and test — do the food coloring test after 15 minutes to confirm the seal

Fix 2: Replace the Fill Valve

👉 Fill valve and flapper repair kit

Turn off water supply, flush, sponge out remaining water
Disconnect the supply line from the tank bottom
Unscrew the fill valve locknut from below the tank
Remove old fill valve, install new one at the correct height
Reconnect the refill tube to the overflow tube
Reconnect supply line, turn water on, adjust water level

Fix 3: Adjust the Float

If the water level is above the overflow tube but the fill valve is otherwise working:

Ball float: Bend the float arm downward slightly to lower the water level
Cup float: Pinch the clip and slide the float down the fill valve shaft
Target water level: 1 inch below the top of the overflow tube

Bottom Line

A toilet that keeps running is almost always a flapper or fill valve issue. Press the flapper to test — if it stops, replace the flapper. If water is overflowing into the overflow tube, replace the fill valve. Both repairs take under 30 minutes and cost under $20.

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