Adjusting the Fill Valve and Float
Okay, here's the thing. Flappers fix maybe seven out of ten running toilets. Great odds. But sometimes you drop in a brand new flapper, feel like a genius, and the toilet is still running or still making that phantom refill sound an hour after nobody's touched it. That's not a flapper problem anymore. That's a fill valve and float problem.
Don't panic. This is still a cheap fix. It's just a different cheap fix.
Quick refresher on what these parts do
The float is the thing that rides on top of the water as the tank fills. Could be a ball on an arm, could be a cup that slides up and down a rod, depends on how old your toilet is. Either way, the float's whole job is to tell the fill valve when to shut off. Water rises, float rises, float hits a certain height, fill valve says "we're good" and stops.
If the float is set too high, the tank fills past where it should, water spills into the overflow tube, and you get that endless running sound that made me lie awake in bed my first week as a homeowner, literally googling on my phone at midnight, too proud to text anybody for help.
Step one: watch it happen
Take the lid off the tank. Flush it. Watch the whole cycle. Don't touch anything yet, just watch. You're looking for water rising up and either trickling into that overflow tube in the middle, or the fill valve just never fully shutting off.
If water's dribbling into the overflow tube, your float's too high. That's your fix today.
Step two: adjust the float
Ball-on-an-arm style (older toilets): There's usually a screw where the arm meets the fill valve. Turn it and the arm angle changes, which changes how high the ball sits before it shuts things off. Turn it to lower the ball a bit. Small turns. Flush and check again.
Cup-on-a-rod style (newer toilets): Usually a little clip on the side of the rod, or the whole float twists to raise or lower. Pinch the clip, slide the float down an inch, flush, check.
Don't overthink this. You're aiming for the water line to sit about an inch below the top of the overflow tube. There's sometimes a little marked line on the overflow tube itself telling you exactly where. If there's no mark, an inch below the top is a solid rule of thumb.
Step three: if adjusting the float doesn't fix it
Sometimes the fill valve itself is just worn out. Water still trickles even after you've lowered the float as far as it'll go. Nine times out of ten at that point, you need a new fill valve, not just an adjustment. That's a slightly bigger job. Water off, old valve out, new one in, follow the box. I'm not going to walk through the whole install here because it deserves its own lesson, but I want you to know the difference: adjusting is a five-minute fix with a screwdriver. Replacing is a thirty-minute fix with a trip to the store in between. Budget your evening accordingly. YouTube will tell you it's a ten-minute job. YouTube edited out the part where the coupling nut didn't fit the first time.
A word about patience here, because I don't always practice what I preach
I want to tell you about the time I ran out of mesh tape halfway through a drywall patch and decided a wad of paper towel would basically do the same job. Spackled right over it, feeling clever. Three days later that paper towel just fell out of the wall, spackle and all, like the wall was returning something I'd lost.
I bring it up here because the fill valve teaches the same lesson from a different angle. It's tempting to find a workaround. Bend the arm a weird direction. Jam something under the float to hold it down. Don't. The parts are built to work a specific way, and rigging around them just means you're back here again next week, except now you've also got a weird bent arm to deal with. Do the real adjustment. It takes the same five minutes as the fake one and it actually holds.
A caution worth saying plainly
If you're adjusting anything inside that tank and the water's still running, you're working around water that's actively moving. Not dangerous, just annoying if you're not paying attention, you'll get a wet sleeve. If you want to work dry, hit the shutoff valve behind the toilet first. You already know where that is. We covered it two lessons ago.
My honest opinion on this one
The scariest repairs are usually the cheapest, and this is a perfect example. A running toilet sounds like a plumbing emergency. It is a nine dollar flapper or a five minute float adjustment, wearing a scary costume. Don't let the sound of it psych you out.
Before next time
Go home, take the lid off your tank, and just watch a flush happen start to finish. You don't have to fix anything yet. Just get eyes on your own float and fill valve so you know what normal looks like before you ever have to fix abnormal.