How to Adjust a Toilet Fill Valve

Six Different Types of Fill Valve

Illustration of a tank fill valve

Illustration: The Spruce / Julie Bang

The toilet in your home has several tank components, but there are only two tank valves at work every time you flush the toilet: the flush valve, which releases the water stored in the tank down into the toilet bowl when you press the flush lever; and the fill valve (also traditionally known as a ballcock), which controls the water flow that refills the tank after the flush.

While the flush valve rarely needs attention, it's quite common to make adjustments on the fill valve to ensure a proper flush. The fill valve has a float or other device that moves with the water level in the toilet tank, opening to refill the tank with fresh water after a flush, and shutting it off when the tank is full. Adjustments to the fill valve may be needed when the toilet fails to flush completely, which can occur because there is not enough water in the tank; or if the valve is set too high and the water fails to shut off and continues to spill over into the overflow tube. Each type of fill valve has a method for adjusting the water level in the tank.

Note: If your fill valve has a small rubber hose running into a brass or plastic overflow tube in the center of the tank, make sure the hose is directed down into the overflow tube and that the end of the hose is above the standing water level in the tank; it should not extend down into the overflow tube below the level of the tank water. Usually, there is a clip that holds the hose in the proper position at the top of the tube.

Tools and Supplies You Will Need

  • Penetrating oil (if needed)
  • Screwdriver (if needed)


The exact method for adjusting the water level depends on the type of fill valve your toilet uses. 

Plunger/Piston Ballcock

The Mansfield Style 09 plunger ballcock from Prier Products is a great example of the plunger/piston design fill valve.
Prier Products

Plunger/piston style fill valves are operated by a floating ball attached to a horizontal brass float rod. The rod moves to raise and lower a plunger or piston in the ballcock body to start and stop the flow of water to the tank. Named for the shape of the mechnism, this is the design that is properly known as a ballcock. The plunger uses an O-ring or leather washer to form a seal to prevent the water from leaking out the top of the fill valve.

To adjust the water level with a plunger ballcock, you simply bend the float rod gently upward to increase the water fill level in the tank, or bend it downward to lower the fill level. The water level must be below the top of the tank's overflow tube.

  • This type of ballcock is now somewhat uncommon and is almost never found in new toilets. But it is such a dependable mechanism that many plunger-type ballcocks are still in operation. 

Diaphragm Ballcock: Brass

Older style cast-brass body diaphragm ballcocks are reliable and long lasting.

A diaphragm ballcock is quite similar to the plunger-style, except that the valve itself does not use a plunger stem, but rather has a diaphragm seal inside a round valve body. It also has a float rod and ball to control water discharge, making it a true ballcock. The lever assembly moves a plastic button in the top of the bonnet, which in turn presses against the rubber or plastic diaphragm to control the flow of water.

As with the plunger ballcock, you adjust the water level by gently bending the brass float rod upward to increase the water fill level, or downward to lower the water fill level. The water level must be below the top of the tank's overflow tube.

  • Historically, this type of ballcock is a later innovation than the classic plunger-style, but it, too, is now rarely found in new toilets. 

If the Tank Does Not Refill

Older models of the diaphragm fill valve have a bonnet or cap made of cast brass like the rest of the fill valve body, but the button that actuates the diaphragm is made of plastic. Sometimes, calcium or other mineral deposits can build up between the brass bonnet and the plastic button, creating friction that causes the button to remain depressed in the “closed” position, even when the float road and ball have dropped away. When this happens, the toilet tank is drained empty and the ballcock does not release fill water to fill it back up.

To fix this problem, spray some penetrating oil into the top of the bonnet where the plastic button protrudes through. Then, work the button up and down by manually moving the float rod up and down so as to depress the button a few times. The button should work free and the ballcock should then operate properly.

Diaphragm Ballcock: Plastic

Contemporary plastic diaphragm ballcocks adjust the water level by use of an adjusting screw on the top of the fill valve.

This is the plastic version of older diaphragm ballcocks made of brass. In this design, the lever assembly moves a plastic button in the top of the bonnet, which in turn presses against the rubber or plastic diaphragm to control the flow of water.

However, on newer plastic diaphragm ballcocks, there is an adjustment screw on the top that adjusts the height of the float rod and ball. Turning the screw counterclockwise raises the water level, while turning the screw clockwise lowers the water level. The water level must be below the top of the tank's overflow tube.

  • This is the last version of a fill valve that can be called a true ballcock. New units can still be purchased, though it has largely been replaced by the more popular float-cup style. 

Float-Cup Fill Valve

The Fluidmaster 400a floating cup is a popular workhorse of a fill valve.
Fluidmaster, Inc.

The float-cup fill valve is the current standard, the design that is used on most new toilets, thanks to its low cost and durable performance. Water flow is controlled by a cylindrical plastic float that moves up and down along the fill valve shaft. This is sometimes called “floatless” because it doesn't have a traditional float rod and ball, but it does indeed use a float device.

The floating cup is attached by a metal spring clip to a thin metal rod that controls the fill valve. To adjust the water level, pinch both ends of the metal spring clip and raise or lower the float. To lower the water level, slide the float downward on the actuating rod, then release the spring clip; to raise the water level, slide the float upward on the rod, and release the clip.

On some float cup valves, there is a plastic screw mechanism that you turn to raise or lower the float. In any case, the water level should be about 1 inch below the top of the overflow tube and the critical level mark on the fill valve.

Internal Float Fill Valve

One relatively new type of flll valve, sometimes marketed as a QuietFill, has a hidden internal float lever inside the head of the valve. It operates in much the same way as a float-cup fill valve, but is advertised a quieter valve with more precise shut-off. 

To lower water level with this type of valve, the entire head of the fill valve is moved up to raise the level of the water in the tank, or lowered to lower the level of water.

First, the top head of the fill valve is twisted counterclockwise to unlock it. The head is moved up or down on the shaft to the desired position, then the head is twisted clockwise to lock it into place again.  

Floatless or Pressure-Activated Fill Valve

The Keeney K830-14 floatless fill valve works without a float device.
Keeney Manufacturing Co.

True floatless fill valves use a pressure-sensing mechanism rather than a float to adjust the water level in the toilet tank. The valve operates under water and can sense the water level based on pressure. To adjust this type of valve, you simply turn an adjustment screw located on the top of the valve. To raise the water level, turn the adjustment screw clockwise; to lower the water level, turn the screw counterclockwise. The water level must be below the top of the tank's overflow tube.

  • Note: This style of fill valve, in which the mechanism is submerged underwater, may be forbidden by the building code in some areas, since there is the potential for back-siphoning contaminated water into the freshwater supply. Always check with local Code authorities on what styles of fill valve are acceptable in your area.