What it usually looks like
- The toilet hisses or trickles long after the flush is done
- It refills by itself every few minutes or hours with nobody using it
- You have to jiggle the handle to make it stop
- The water level in the tank sits right at or over the top of the overflow tube
- A faint ripple or movement is visible in the bowl
- The water bill climbed with no other explanation
Likely causes, most common first
A worn or warped flapper
The rubber flapper seals the opening between tank and bowl. Chlorine, hard water and simple age make it stiff, warped or coated with mineral so it cannot seat. Water leaks past it into the bowl, the level drops, and the fill valve runs to top it off. This is the cause in the large majority of running toilets and the part is inexpensive. Drop-in tank cleaning tablets destroy flappers quickly.
A fill valve that will not shut off
The fill valve senses the water level and closes when the tank is full. Grit from the supply line, a worn seal, or simple wear keeps it from seating, and it runs continuously or sputters. A fill valve that hums, whistles or runs even with the float held up has failed.
Float set too high
If the float is adjusted so the tank fills above the overflow tube, water runs straight down the tube into the bowl and the fill valve never satisfies. Look at the water line in the tank; it should be about an inch below the tube top.
A chain that is too long, too short or caught
A chain that is too long can slip under the flapper and hold it open. One that is too short holds the flapper slightly up all the time. Either one makes the toilet run until someone jiggles the handle.
A cracked overflow tube or flush valve seat
The plastic flush valve assembly can crack at the base or the seat can corrode on older toilets. Water leaks around the flapper no matter how new the flapper is. This repair means pulling the tank.
High water pressure overwhelming the fill valve
In homes with pressure above 80 psi, some fill valves cannot close fully against the supply. The toilet runs intermittently and the real fix is a pressure reducing valve for the house.
Safe things to check yourself first
- Take the tank lid off and look at the water line; if it is at or over the overflow tube, lower the float
- Put food coloring in the tank, wait fifteen minutes without flushing, and check the bowl for color; color means the flapper is leaking
- Press down on the flapper with a stick; if the running stops, the flapper needs replacing
- Check the chain for slack or tangling and adjust it so the flapper closes fully with a little play
- Lift the float by hand; if the valve keeps running, the fill valve has failed
- Remove any drop-in cleaning tablets from the tank
Stop and call if
- The tank is cracked or water is on the floor around the toilet
- The shutoff valve under the toilet will not close or drips when turned
- A new flapper and fill valve did not stop the running, which points to the flush valve seat
- The toilet is also rocking or leaking at the base
- Several toilets in the house are running, which can mean a pressure problem
How we diagnose and fix it
- Test the flapper, fill valve and float and replace what has worn, usually with the parts on the truck in one short visit
- Replace the flush valve assembly when the seat or overflow tube is cracked, including pulling and resetting the tank with new bolts and gaskets
- Swap a failing multi-turn supply stop for a quarter-turn ball valve so the toilet can be isolated next time
- Check house water pressure when fill valves keep failing and recommend a pressure reducing valve if it is high
- Advise replacing a toilet when the parts are obsolete or the bowl and tank are at the end of their life, and install a comfort-height or efficient model if you want one
Around Kitsap, Pierce and Mason counties
Well water in Olalla, Seabeck, the Key Peninsula and most of Mason County carries iron and sediment that scores fill valve seals and crusts flappers, so running toilets are a steady call out there. In the high-pressure zones at the bottom of hills in Port Orchard and Silverdale, we see fill valves that cannot hold against the supply. And in every vacation cabin along Hood Canal, a running toilet with nobody home is the kind of thing that turns into a shocking bill or an empty well pressure tank.
Questions people ask
How much water does a running toilet waste?
A leaking flapper can pass more than a hundred gallons a day. A fill valve stuck wide open can pass several times that. Either one shows up on the bill within a month.
Can I replace the flapper myself?
Yes. Shut the supply, flush, unhook the old flapper, and clip on a new one matched to the brand. If it still runs afterward, the seat it sits on is the problem.
Why does my toilet run for a few seconds every hour?
That is called phantom flushing, and it is a slow flapper leak lowering the tank until the fill valve tops it off. The dye test confirms it.
Is it cheaper to fix the toilet or replace it?
A flapper and fill valve is a modest repair on any toilet. If the toilet is decades old, uses a lot of water per flush, and has other issues like a rocking base, replacement is often the better value and we will say so.
Do tank cleaning tablets really cause this?
Yes. The chlorine in drop-in tablets eats flappers and seals in a year or two. Clean the bowl instead.