Around the House · Plumbing

How to fix a running toilet

A running toilet is the most expensive thing you're ignoring. It's also one of the easiest things to fix — usually a $5 part and 15 minutes. Here's the diagnostic order.

Job time 15 – 45 min

Skill level Beginner

Job cost $5 – $40

The Honest Read

What this job actually involves

A toilet that runs intermittently or constantly is wasting somewhere between 50 and 300 gallons a day. That's a noticeable bump on your water bill and, depending on where you live, a real environmental problem too.

There are exactly four things that cause a toilet to run: a bad flapper, a stuck chain, a misadjusted float, or a worn fill valve. You can diagnose all four in five minutes with the tank lid off.

If the toilet is more than 25 years old and you're already inside the tank, just replace the guts — flapper, fill valve, flush valve. The whole kit is $25 and lasts another 20 years.

What you need

Tools & materials

Shop the supply side here. The big-ticket stuff and the brand-restricted items, we'll point you local further down.

Tools

Adjustable wrench or channel-lock pliers
Sponge and bucket
Towel
Phillips screwdriver

Materials

Replacement flapper (universal or matched to model)
Fluidmaster-style fill valve (or matched brand)
Complete toilet repair kit (flapper + fill valve + flush valve)
Replacement chain and clip

The Steps

Diagnose and fix in this order

Lift the tank lid and look

Set the lid on a folded towel on the floor (porcelain is brittle — cracking the lid is the most expensive mistake in this whole job). Flush. Watch what happens. Then wait. Most running toilets reveal the problem within 60 seconds of watching.

Check the flapper

Push the flapper down with your finger. Does the running stop? Bad flapper. They harden and warp with age, especially with chlorine tablets in the tank (don't use those — they destroy flappers and seals). Replace the flapper — about $5.

Check the chain

Too long, it gets stuck under the flapper, holding it open. Too short, the flapper can't close. The chain should have about 1/2″ of slack when the flapper is closed. Adjust the chain length at the flush lever.

Check the float and water level

The water level in the tank should be about 1″ below the top of the overflow tube. Too high, water runs constantly into the overflow tube. Adjust the float — there's a screw or clip on top of the fill valve. Lower the float, water stops running over.

Replace the fill valve if needed

If the fill valve hisses, won't shut off, or fills very slowly, replace it. Shut the water off at the wall, flush, sponge out the remaining water, unscrew the supply line and the nut underneath the tank, lift the old valve out, drop the new one in. 15 minutes.

Test and verify

Flush and watch the tank refill. The fill valve should shut off cleanly. Wait 10 minutes without flushing — the water level should be exactly where it was. If it's dropped, the flapper still leaks. Dye-test: drop food coloring in the tank, wait an hour without flushing, check the bowl — if the bowl is tinted, the flapper isn't sealing.

Try local first · We'll wait

The toilet aisle at a real hardware store

Toilet parts seem universal until they're not. Bringing the old part to the store saves a return trip every time.

Flappers in every size and shape — 2″, 3″, tower-style, canister-style, brand-matched
Complete repair kits that include everything inside the tank — cheaper than buying piece by piece
Replacement bolts, washers, and tank-to-bowl gaskets for the next time
Wax rings and toilet shims for when you upgrade to step into the actual replace-a-toilet job
Real expert advice on whether to fix the old toilet or just replace it

Find a local hardware store →

When to call a pro

Call a plumber if: water is leaking from the base of the toilet (wax ring or cracked porcelain — both serious); the tank itself is cracked; the floor around the toilet feels soft (subfloor damage); or you've replaced the flapper and fill valve twice and it still runs. At that point something structural is wrong.

Keep going

Related project guides

Plumbing

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