Repairs
Stopping a toilet that will not stop refilling
A running toilet is one of two faults, and the tank lid tells you which within about two minutes. Both are usually fixable tonight with parts from a hardware shelf, so long as the shut-off under the tank still closes.
Lift the tank lid and look at the top of the overflow tube, the open plastic pipe standing in the middle of the tank. If water is running into that tube, the fill valve is not shutting off or the float is set too high. If the tube is dry and the tank still refills every few minutes on its own, water is escaping downwards through the flapper into the bowl. Those are the only two faults behind almost every constantly running toilet, and they take different parts. Sort out which one you have before buying anything, because half the repair kits on the shelf address the wrong half of the problem.
The two-minute test that splits the problem in half
Take the lid off and set it flat on the floor, not balanced on the seat. Watch the water level against the top of the overflow tube. Then shut off the supply at the valve behind the toilet and leave everything alone for fifteen minutes.
If the water level in the tank drops during those fifteen minutes with the supply off, the flapper or the seat it sits on is leaking, full stop. If the level holds steady, the tank side is sound and the fault is on the fill side. You can confirm the first case with a few drops of food colouring in the tank: come back later and if there is colour in the bowl, the flapper is passing water.
When water is pouring into the overflow tube
The fill valve is supposed to shut off when the float reaches its set height. The water line should sit somewhere below the top of the overflow tube, not level with it. Most modern fill valves adjust with a screw on top or a clip on a sliding rod. Bring the level down and see whether the running stops.
If lowering the float does nothing and the valve keeps trickling, the valve itself is finished. These are a whole-unit replacement rather than a rebuild, they thread through the tank bottom on one nut, and they come with a new supply washer. Give yourself somewhere to put the tank water, because a sponge and a bucket get the last inch out.
One detail people miss: the small flexible tube from the fill valve should clip to the rim of the overflow tube, not be pushed down inside it. Pushed in, it can siphon the tank down and set the fill valve running again for reasons that have nothing to do with the valve.
When the tank is quietly draining into the bowl
Reach in and press down on the flapper with a finger. If the sound of running water stops while you hold it, the seal is the problem. Take the flapper off and look at the underside. A flapper past its service life goes tacky, warps at the edge, or develops a shiny hard ring where it has been pressing on the seat.
Check the chain while you are in there. Too tight and the flapper is held a fraction open all the time. Too slack and it can loop under the flapper as it drops. There should be a little slack, roughly enough to lift out one link of play, and no more.
Why a new flapper sometimes leaks the same day
Costa Mesa water comes entirely from local groundwater, pumped from wells into the Orange County basin, and groundwater carries dissolved mineral. Inside a toilet tank, water sits still for hours at a time between flushes. That is the ideal condition for a mineral ring to build up on the flush valve seat, which is the machined lip the flapper closes against.
Run a fingertip around that seat. If it feels gritty or ridged rather than smooth, a brand new flapper will bridge the ridge and leak just like the old one did. On a plastic seat, clean it gently with a scouring pad and nothing sharper. On a brass seat, fine abrasive cloth used lightly will bring it back. If the seat is chipped or badly pitted, the flush valve is a bigger job, and that means pulling the tank off the bowl.
Parts worth replacing together while the tank is open
What tonight’s fix cannot cover
Water appearing at the floor around the base of the toilet is not a running toilet. That is either the tank-to-bowl connection dripping down the back, a failed wax seal at the closet flange, or a hairline crack in the china. The wax seal means pulling the toilet, checking the flange is sound and set at the right height, and resetting it. On older houses the flange itself has often corroded or broken, and that is repair work rather than a parts swap.
A toilet that gurgles, backs up, or drains slowly is a drain problem wearing a toilet costume, and running water is not the symptom to chase there. So is a toilet that bubbles when the washing machine empties. Those point at the branch line or further out, and they want a camera rather than a screwdriver.
The other stopping point is the shut-off valve behind the toilet. If it will not close, or if it starts weeping at the stem the moment you turn it, do not force it. Turn the water off at the house main instead, and treat the valve as part of the job.
Before you go to bed
Turn the supply back on, let the tank fill, and mark the water line on the inside of the tank with a pencil. Flush once, let it refill, and leave it. In the morning, check the mark. A level that has dropped overnight means water is still going somewhere, even if the toilet has been silent, and a silent leak into the bowl runs all night on a groundwater supply you are paying to pump and treat.
If the mark is exactly where you left it and the room was quiet, the repair held. Put the lid back on properly, flat and centred, and keep the old flapper in the cabinet as a pattern for next time.