What's wrong with your toilet? Let's fix it.

Toilet keeps running constantly

A toilet that keeps running is almost always one of three things, in this order:

1. Worn flapper — the rubber seal at the bottom of the tank warps or gets crusty and stops sealing. This is the single most common cause of a running toilet.
2. Fill valve not shutting off — the tall valve on the left side of the tank keeps feeding water even when the tank is full, so the extra spills down the overflow tube forever.
3. Chain or float out of adjustment — a too-tight chain holds the flapper open a crack; a too-high float keeps the water level above the overflow tube.

The dye test: flapper or fill valve?

Put 5–10 drops of food coloring in the tank and wait 20 minutes without flushing. Color shows up in the bowl → your flapper is leaking; replace it. No color in the bowl but water keeps trickling into the overflow tube → your fill valve isn't shutting off; replace that instead. Still not sure which part is which? Our flapper vs. fill valve guide sorts it out with photos.

Fix 1: Replace the flapper (10 minutes, no tools)

Shut the water off at the wall, flush to empty the tank, unhook the old flapper from the two pegs and the chain, and hook on the new one. That's the whole job — full walkthrough in how to replace a toilet flapper.

What size flapper? A 30-second check

First, the honest shortcut: pull out your old flapper and look for a size stamp — many are marked 2" or 3" right on the rubber. If there's no stamp, look at the flush valve opening (the hole the flapper covers at the bottom of the tank):

Not sure even after looking? The flapper guide covers both sizes and the odd proprietary ones.

Fix 2: Replace the fill valve (15–20 minutes, adjustable wrench)

If the dye test cleared the flapper but water keeps hissing into the overflow tube, the fill valve is done. Shut off the water, drain the tank, unscrew the supply line and lock nut, and swap in the new valve — step by step in how to replace a toilet fill valve.

Want the whole repair in one place? Read how to fix a running toilet.

Toilet running intermittently (the phantom flush)

If your toilet runs on and off by itself — a random 10–20 second refill every hour or few, often loudest at night — that's the classic phantom flush, and it has one overwhelmingly likely cause: a slow flapper leak. The worn flapper lets tank water seep into the bowl so gradually you never hear it. When the level drops far enough, the fill valve kicks on to top the tank back up. That short refill is the "flush" you keep hearing.

Confirm it with the dye test: 5–10 drops of food coloring in the tank, wait 20 minutes without flushing. Color in the bowl = leaking flapper. It's the same test as above, and with a toilet running intermittently it comes back positive almost every time.

A silently leaking flapper isn't just annoying — it can waste hundreds of gallons a day and quietly inflate your water bill. The fix is the same 10-minute flapper swap covered in how to replace a toilet flapper. If the dye test is clean and it still cycles, work through flapper vs. fill valve to rule out a fill valve that's losing its seal.

Check price on Amazon →
Korky 100BP 2-inch flapper — $8–$14, rated 4.8/5. Check your size with the finder above first.

Toilet won't flush — or the flush is weak

A toilet not flushing at all and a weak toilet flush are usually the same problem at different stages. Most likely causes, in order:

1. A clog — a full clog means the toilet won't flush and the bowl fills; a partial clog means water swirls weakly and drains slow.
2. Low water level in the tank — not enough water to power the flush.
3. Mineral-clogged rim jets — the little holes under the rim scale up with hard water, so less water enters the bowl with less force.

Fix 1: Plunge it right

Use a flange (beehive-style) plunger, not a flat sink plunger — it needs to seal the drain opening. Push down slowly to seat it, then pull and push with force 10–15 times, keeping the seal. Full technique in how to unclog a toilet. No plunger in the house? Try these no-plunger methods first.

Fix 2: Deeper clog? Use a toilet auger

If plunging won't clear it, the clog is past the trap — usually something that shouldn't have been flushed. A toilet auger (closet auger) snakes 3 feet into the drain and either breaks the clog up or hooks it out, and the vinyl guard keeps the cable from scratching the porcelain. Our picks and how to use one: best toilet augers.

Fix 3: Raise a low tank water level — free

Take the lid off. The water should sit about an inch below the top of the overflow tube (many tanks have a marked water line). If it's well below that, the flush never gets its full push. Adjust the float on the fill valve up — a screw on most modern valves, a bent arm on old ballcocks — until the level hits the line. Costs nothing and takes two minutes.

Fix 4: Clear mineral-clogged rim jets

Hold a small mirror under the rim: if the jet holes are white and crusted, hard-water scale is choking the flush. Apply a clinging bowl cleaner under the rim, let it sit, and scrub the holes with a stiff brush (a bent wire or old toothbrush helps for stubborn scale). Our tested picks are in best toilet bowl cleaners.

Toilet gurgling or bubbling

A toilet bubbling or gurgling means air is being pulled or pushed through the water in the bowl — and air only moves like that when something downstream is partially blocked. Three causes, from least to most serious:

1. Partial clog in the toilet's own drain — the most common and the one you can fix yourself.
2. Blocked vent stack — the pipe through your roof that lets air into the drain system; leaves or a nest can block it.
3. Main sewer line blockage — roots, grease, or a collapsed section on the line that serves the whole house.

Only this toilet? Plunge it first; if the gurgle persists, run a toilet auger through the trap — a partial clog that survives plunging usually gives up to the auger. See best toilet augers for technique. The RIDGID K-3 above is the one we recommend. Check price on Amazon →

Multiple fixtures gurgling? Call a plumber — and we mean that. A main line or vent blockage needs a camera inspection, a roof-access vent clearing, or a motorized drain machine. There's no part we could sell you that fixes it, and DIY attempts on a main line usually just delay the real repair. A drain-cleaning visit typically costs far less than the water damage from a sewage backup.

Toilet smells like sewage

When a bathroom smells like sewage, the smell is sewer gas escaping somewhere it shouldn't. Three causes, in order of likelihood:

1. A dried-out trap in a rarely used bathroom. The water sitting in the bowl (and in the floor drain, if there is one) is the seal that blocks sewer gas. In a guest bath that sits unused for weeks, that water evaporates and gas drifts in. The fix is free: flush the toilet, run every faucet for a minute, and pour a quart of water down any floor drain. If the smell fades in a day, that was it — flush weekly to keep the seal.
2. A failed wax ring under the toilet. The wax ring seals the toilet base to the drain flange. When it fails you'll often notice the smell is strongest near the floor, water seeping around the base, or a toilet that rocks. Fixing it means pulling the toilet, scraping the old wax, and setting a new ring — a hands-and-knees job that's doable if you're confident, but there's no shame in paying a plumber for it. We don't sell wax rings; any hardware store carries them for a few dollars.
3. Biofilm in the tank or under the rim. Bacteria film builds up in the tank and rim jets and gives off a musty-sewage odor even when the plumbing is sound. Scrub the tank walls and under the rim with a clinging bleach gel — see best toilet bowl cleaners for what actually works. Check price on Amazon →

Smell strongest at the base, plus water stains or rocking? Jump to the rocking section — a bad wax ring often causes both.

Toilet rocking or wobbling

A toilet rocking when you sit down is worth fixing promptly — every rock works the wax ring seal underneath, and a broken seal means leaks and sewer smell. The good news: no purchase needed from us for this one. In order:

1. Tighten the closet bolts — gently. Pop the plastic caps at the base and snug each nut a quarter turn at a time, alternating sides. Stop at snug. Porcelain cracks before the bolt strips — over-tightening is how people turn a wobble into a new toilet.
2. Shim an uneven floor. If the bolts are snug and it still rocks, the floor isn't flat under the base. Plastic toilet shims (a hardware-store item, a few dollars) slide under the low side; trim the excess and run a bead of caulk around the base, leaving a gap at the back so a future leak can show itself.
3. Been rocking a long time? Assume the wax ring has taken damage. If you smell sewage near the floor or see water at the base, the ring needs replacing — that means pulling the toilet, so call a plumber if that's outside your comfort zone. It's a common, inexpensive service call.

While you're down there: a wobbly seat is a different (and easier) fix — see how to fix a loose toilet seat.