How do I adjust a Fluidmaster fill valve?

Turn the water level adjustment screw on the valve. Clockwise raises the level and counterclockwise lowers it. Fluidmaster's hint is that 8 full turns of the screw moves the float half an inch, so small turns make small changes.

The routine has four steps:

1. 1Flush the toilet first, so you're adjusting while the tank refills.
2. 2Turn the screw a few turns in the direction you need.
3. 3Flush again and watch where the water stops.
4. 4Repeat until it lands on the target.

The target is about half an inch below the top of the overflow pipe, the tall open tube in the middle of the tank. Fluidmaster recommends half an inch. If the water sits at or above the top of that tube, it spills down the tube and the toilet never stops running. Lowering the level a little is the fix for a lot of "my toilet runs" complaints on a valve that is otherwise healthy.

Going the other way, a bowl that looks low after a flush often just needs more water in the tank. Raise the tank level to that half inch mark. Fluidmaster adds two other checks for a low bowl: confirm the refill tube is sending water down the overflow pipe, and give the flapper chain about half an inch of slack so the flapper isn't closing too soon. To see that whole repair, read our guide on how to replace a toilet flapper or fill valve.

Height matters because the valve has a critical level mark, stamped "C.L.", and that mark has to sit 1 inch above the top of the overflow pipe. Fluidmaster says this is a requirement of the Universal Plumbing Code. The simple way to hit it is to set the top of the valve 3 inches above the top of the overflow pipe. That automatically puts the C.L. mark where it belongs.

Before you take the valve out, get set up. Fluidmaster's instructions list the tools you need: a bucket, scissors, channel locks or adjustable pliers, and a sponge. Shut off the water at the supply valve by turning it clockwise, flush the tank, and sponge out what's left so nothing spills. Use a pencil to mark the tank's existing water level before you remove an old valve, so you can compare the new setting. Have a towel handy. A few drips from the supply connector are normal when you loosen it.

Here's how to do it right:

1. 1Before you install the valve, set it in the tank without fastening it and measure.
2. 2Take it out. Hold the lower shank in one hand and the top of the valve in the other.
3. 3Twist the lower shank counterclockwise to make the valve taller and clockwise to make it shorter. You should hear several clicks.
4. 4Set it back in the tank and check the height again.

Leave the lock ring alone. It holds the body and the shank together under pressure, and Fluidmaster warns against mixing a new body with an old shank because it can leak.

Two more setup checks: the top of the overflow pipe should be at least 1 inch below the tank's flush lever hole, and the lid should sit on the tank without touching the valve. Push down on the shank from inside the tank as you tighten the locknut, and tighten it by hand only. Overtightening can crack the valve or the tank and cause a flood.

Work through Fluidmaster's troubleshooting list in this order:

• Debris in the valve. Fluidmaster's warning is that sand and rust move through water pipes. Shut the water off, push the float cup up with one hand while you hold the valve shaft, and twist the cap counterclockwise about an eighth of a turn to unlock it. Hold a cup over the open valve, turn the supply on and off a few times to flush the debris out, and lock the cap back on.
• A worn seal. If the valve has been in use a long time or the float cup doesn't drop when you flush, replace the seal in the top of the valve. Fluidmaster calls for its 242 seal.
• Weak flow. With the cap off, hold a cup upside down over the valve and turn the water on. Weak flow means the blockage is in the inlet, the supply line or the shutoff valve at the wall.
• A valve that cycles on and off by itself. That means the tank is losing water and the valve is refilling it. Clean the flapper and drain seat. If it keeps leaking, replace the flapper or the flush valve.
• A refill tube pushed into the overflow pipe. It should clip on with a slight arch, above the tank water. Shoved down inside, Fluidmaster says it can waste significant water and can siphon water from the tank to the bowl.

If you've tried the level adjustment and the valve still doesn't shut off, lower the level first. If it still won't stop, go to the debris check. Our page on a toilet tank that is not filling covers the opposite problem, and a noisy or whistling fill valve has its own causes.

A few small habits protect you. Inspect the water supply connector when the tank is open. Fluidmaster says to replace it if it is worn or more than 5 years old, to prevent flooding. Don't overtighten the coupling nut either.

Keep chlorine and bleach drop-in tank tablets out of the toilet. Fluidmaster says they damage tank parts, may cause flooding and void its warranty, and it points to bowl-only cleaning systems as the safer choice.

Then check for the leak you can't hear. The EPA says an aging flapper can silently leak thousands of gallons a year, and its test is easy: a few drops of food coloring in the tank, and if any color shows up in the bowl after 10 minutes, you have a leak. The EPA also says the average household loses more than 9,300 gallons a year to leaks, so a five-minute check is worth it.

Most of this is a homeowner job. It's time to call someone if the shutoff valve won't turn or leaks when you touch it, the tank leaks where it meets the bowl, the porcelain is cracked, or the toilet still runs after a clean valve, a fresh seal and a new flapper. Those point at the flush valve, the shutoff or the wax ring, not the fill valve. HQ Plumbing & Air gives free estimates and upfront pricing, and our licensed plumbers handle emergencies 24/7.