Toilet keeps running: the 3 parts to check

What to do, in order

1. Take the tank lid off and flush: does the flapper seal fully when the water drops? A warped flapper is the #1 cause — $10 part, 10-minute swap.
2. Check the chain: it should have slight slack. Too tight holds the flapper open; too slack tangles.
3. Look at the water level: it should sit ~1 inch below the overflow tube top. If it's pouring into the overflow tube, bend the float arm down (or adjust the screw on canister floats).
4. Dye test for silent leaks: food coloring in the tank, wait 20 minutes without flushing. Color in the bowl = flapper or seal leak.
5. Water hammer or hissing fill valve: replace the fill valve (~$20, 30 minutes).

Red flags — stop and call a pro

• Water leaking from the tank base onto the floor — that's the wax ring or a cracked tank, not a running issue
• Constant refilling every few minutes with warm tank — could indicate a flush valve leak wasting serious water

Prevention

Flappers are wear items: replace every 3–5 years (chlorine tablets in the tank shorten their life dramatically — use them sparingly or never).

This guide is maintained by the ee.ltd editorial team — reviewed for 2026. Browse all home repair guides or compare plumbing costs.

Related guides

• Water heater leaking from the bottom: what to do right now
• Sudden low water pressure in the whole house: diagnosis
• Clogged drain: when to plunge, snake, or call a pro
• Find your main water shutoff before you need it at 2 AM

What this repair typically costs

• Water heater replacement cost guide
• Water heater repair cost guide
• Toilet installation cost guide
• Faucet replacement cost guide