My toilet started running at 2am and would not stop. Not the dramatic waterfall kind, just a soft hiss that meant the tank was slowly refilling forever. It woke me up every night for a week before I looked inside the tank and realized the fill valve was ancient, crusty, and done.

I called a plumber for an estimate. He quoted me enough money that I decided to try it myself, and twenty minutes later I was wondering why I had not done this years ago.

What a Fill Valve Does

The fill valve is the tall plastic tower inside the tank that refills it after a flush. When it wears out, you get the running sound, a tank that never quite fills, or a toilet that refills every few minutes. It is a wear part, like a washer, and it is one of the easiest things in a house to replace.

What You Need

The whole job needs one part and maybe two tools:

• A new fill valve. Universal ones fit almost every toilet and cost about fifteen dollars. Take a photo of your old one to compare.
• An adjustable wrench or pliers for the supply line nut. Sometimes you can do it by hand.
• A towel for the water that will spill. There is always water that spills.

The Swap, Step by Step

Here is the whole job:

1. Turn off the water at the shutoff valve behind the toilet. If there is no shutoff valve, turn off the main water supply to the house.
2. Flush the toilet and hold the handle down to drain the tank. Sponge out the last bit of water.
3. Disconnect the supply line from the bottom of the tank with your wrench.
4. Unscrew the nut under the tank that holds the fill valve, and lift the old valve out through the top.
5. Drop the new valve in, adjust its height so the top sits about an inch below the tank’s overflow tube, and hand tighten the bottom nut. Do not crank it. Hand tight plus a quarter turn is plenty.
6. Reconnect the supply line, turn the water back on, and let the tank fill.
7. Adjust the float so the water stops about half an inch below the top of the overflow tube.

The Part That Confuses People

The new valve will have a clip or a collar that sets the height. Set it before you install it, not after. Slide the clip up or down, lock it, and the valve is the right height. Getting this wrong is the only way to end up with a valve that is too tall for the tank lid.

When to Call a Plumber Instead

If the toilet still runs after a new fill valve, the problem is usually the flapper, the rubber part at the bottom of the tank, and that is an even easier swap. If water pools around the base of the toilet, that is a wax ring issue, which is a bigger job. But the fill valve itself is a perfect first plumbing project.

The 2am hiss is gone now. That was six months ago, and I have saved the plumber’s fee twice over in water bills, because a running toilet wastes gallons every single day.

📋 Quick Summary: Shut off the water, drain the tank, disconnect the supply line, swap the old fill valve for a universal one, and adjust the float height. The whole job takes about twenty minutes and costs around fifteen dollars.