Toilet keeps running? Here's what's stuck open — and what's safe to fix yourself

A toilet that never quite stops — the hiss you hear from another room, or the one that runs all night and quietly drives up your water bill — is almost always one small part inside the tank that has stopped sealing. It is one of the most common repairs in the house, and several of the causes are safe to sort out yourself in a few minutes. The good news is that a running toilet is a nuisance, not an emergency, so there is time to look before you book anyone.

Start by lifting the tank lid and setting it flat and out of the way. Everything that makes the noise is in there, and watching it for a moment usually tells you which of two things is happening.

First, tell which of the two patterns you have

There are really only two ways a toilet runs on and on, and they point to different parts. Watch the tank with the lid off and you can tell them apart quickly.

• Water is trickling out of the tank into the bowl. The tank slowly empties, the fill valve kicks on to top it back up, and the cycle repeats — sometimes as an occasional 'phantom flush' with no one near it. That points to the flapper at the bottom of the tank not sealing.
• Water is running into the tall overflow tube in the middle of the tank. The water level has risen too high and is spilling down the tube to keep from overflowing, so the fill valve never shuts off. That points to the float set too high or a fill valve that will not close.

The usual causes, from most common down

• A worn or dirty flapper — the rubber seal at the bottom of the tank hardens, warps, or collects mineral buildup and stops sitting flush on its seat. This is the single most common cause. A drop of food coloring in the tank that shows up in the bowl a few minutes later, without a flush, confirms it.
• A tangled or badly adjusted chain — the chain from the flush lever to the flapper is too short and holds the flapper a hair open, or too long and slips under it. A quick relink fixes it.
• The float set too high — the float that tells the fill valve when to stop has drifted up, so water rises above the overflow tube and pours down it. Lowering the float brings the water line back below the tube.
• A failing fill valve — the valve itself no longer shuts off cleanly and keeps feeding water. These are inexpensive and sold as a standard kit, but replacing one is a step up in comfort from the quick adjustments above.
• A cracked overflow tube or a worn flush-valve seat — less common, and usually a sign the whole flush valve is due for replacement.

What's safe to try yourself

• Stop the water first if you need to work in peace — the supply valve is on the wall or floor behind or below the toilet. Turn it clockwise to shut off, and the tank will stop refilling while you look.
• Check and adjust the chain — give it just enough slack that the flapper drops fully closed, with no kink holding it open.
• Lower the float — on a modern column-style fill valve there is a clip or a screw to bring the float down; on an older ball-and-arm, gently bend the arm down. Aim for the water line an inch or so below the top of the overflow tube.
• Clean or replace the flapper — flappers are cheap, sold to fit common toilets, and swap out by hand in a few minutes with the water shut off. Wipe the seat it lands on while you are in there.
• Test with food coloring — a few drops in the tank that seep into the bowl without flushing tells you the flapper is leaking, so you are not guessing.

When to call a plumber

If the flapper, chain, and float all look right and it still runs, the fill valve or the flush valve assembly is likely worn and due for replacement — doable for a handy owner, but a fair reason to book a pro if you would rather it be done once and done right. Call a plumber, too, if the supply shutoff valve behind the toilet is seized, drips, or will not fully close, if the tank or bowl is cracked, if water is escaping onto the floor rather than staying inside the tank and bowl, or if more than one toilet in the house runs — several at once can point to something upstream rather than the toilets themselves.

Describe what the toilet is doing — a constant trickle into the bowl, water spilling into the overflow tube, a shutoff valve that will not turn — and Roger books one vetted, licensed local plumber and confirms the appointment time with you. You see a price range up front, and the plumber confirms the price in person after seeing the work. Homeowners pay Roger nothing, and Roger does not add a markup on the plumber's price.