Toilet keeps running? How to adjust or replace the fill valve

A toilet that will not stop running is the sound of money going down the drain, and in a house that sits empty for the summer it can run for months before anyone hears it. The good news is that the two parts responsible are sold at any hardware store, need no special tools, and are the most homeowner-friendly repair in plumbing. The first step is figuring out which part is at fault.

Fill valve or flapper?

Lift the tank lid and watch for a minute.

• Water is running over the top of the overflow tube (the open vertical pipe in the middle of the tank). The fill valve is not shutting off, or the float is set too high. This guide is for you.
• The water level sits below the overflow tube, but the tank drains slowly and the fill valve kicks on every so often. Water is seeping past the flapper into the bowl. The dye test in our high water bill guide confirms it: a few drops of food coloring in the tank, wait, and color in the bowl means replace the flapper.
• The fill valve hisses or sputters but the level looks right. The valve’s seal or diaphragm is worn, and the fix is the same as replacing it.

Adjust the float first

Fill valves shut off when the float rises to a set height. If the level is above the overflow tube, lower the float.

• Cup or cylinder float on the valve shaft. Pinch the clip on the side and slide the float down, or turn the adjustment screw on top. Small changes; a quarter inch matters.
• Ball float on an arm. Turn the screw where the arm meets the valve, or gently bend the arm down.

Flush and check. The water should stop about an inch below the top of the overflow tube, or at the fill line marked inside the tank. If the valve still runs or the level keeps creeping, the valve is done.

Replace the fill valve step by step

A universal fill valve fits nearly every toilet made in the last several decades. You will need it, a small adjustable wrench or pliers, a sponge, a towel, and a bucket.

1. Turn off the supply. The angle stop is the small valve on the wall or floor behind the toilet. Turn it clockwise until it stops. If it will not turn, or it starts to drip, stop here and read the next section.
2. Flush and hold the handle down to drain the tank. Sponge out the water that stays at the bottom so it does not end up on the floor.
3. Disconnect the supply line from the bottom of the fill valve where it comes through the tank. Keep the bucket under it.
4. Remove the old valve. Unscrew the large plastic nut under the tank, lift the valve out, and pull the refill tube off the overflow tube.
5. Set the height of the new valve. Most twist to adjust. The top of the valve should sit an inch or so above the overflow tube, and the critical level mark on the valve must be above the overflow tube; the instructions in the box show where.
6. Install it. Seat the washer, drop the valve through the hole, and tighten the nut underneath by hand plus a quarter turn with pliers. Plastic threads strip if you crank on them.
7. Clip the refill tube to the overflow tube so it discharges into it, not down into the tank; that small tube is what refills the bowl.
8. Reconnect the supply line finger tight plus a snug quarter turn. Open the angle stop slowly.
9. Check. Let the tank fill, set the water level to the line, flush a few times, and look under the tank and at both ends of the supply line with a dry paper towel.

The old supply line and the stuck angle stop

In homes built before the 1990s, and in plenty built since, the parts you did not plan to touch are the ones that fail. Angle stops that have not been turned in twenty years seize, and forcing one can break the stem or start a drip that will not stop. Rigid chrome supply tubes and old gray or black rubber hoses crack when they are flexed. Any time you replace a fill valve, replace the supply line with a braided stainless one, and if the angle stop is stiff, corroded, or drips when moved, that is the point to stop. Replacing a stop means shutting off the whole house at the main valve, cutting the old stop off, and installing a new one on copper, CPVC, or PEX. That is a licensed plumber’s job, and it is a small one when it is planned rather than an emergency at ten at night with water on the floor.

When to replace the toilet instead

A fill valve and a flapper fix most running toilets. Sometimes the honest answer is a new toilet.

• It is an original high-volume model from before the mid-1990s. Every flush uses more than twice the water of a modern one, and the parts are increasingly odd sizes.
• The tank bolts are rusted and the tank rocks, or there is a hairline crack in the tank or bowl. Cracks spread.
• The toilet has needed a repair every year, clogs constantly, or the bowl is stained past cleaning from years of hard water.
• Water shows up around the base. That is the wax ring or the flange, not the tank, and it is a floor problem if it waits.

A new toilet is a straightforward install on a sound flange, but a cracked or corroded flange on an older slab home, or a cast iron closet bend, is where a swap turns into real plumbing.

If you have replaced the valve and it still runs, if the angle stop would not cooperate, or if you would rather have the whole thing looked at, send us a photo of the tank and the stop and tell us what happened. We will tell you what it needs.