How to Adjust a Toilet Fill Valve

How to Adjust a Plunger/Piston Ballcock

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, which starts and stops the flow of water to the tank. Named for the shape of the mechanism, 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.

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. 

1. Adjust the Water Level

   Gently bend the float rod up to increase the water fill level in the tank, or bend it down to lower the fill level.

2. Watch the Water Level

   The water level must be below the top of the tank's overflow tube. If it is not, continue adjusting until you achieve the desired result.

How to Adjust a Diaphragm Ballcock: Brass

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.

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

1. Adjust the Water Level

   Adjust the water level by gently bending the brass float rod up to increase the water fill level or down to lower the water fill level. 

2. Watch the Water Level

   The water level must be below the top of the tank's overflow tube. Continue making small adjustments until the water level is where it should be.

How to Adjust a Diaphragm Ballcock: Plastic

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. 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. 

1. Turn the Screw Clockwise or Counterclockwise

   Using a screwdriver, turn the screw at the top of the valve. Turning the screw counterclockwise raises the water level, while turning the screw clockwise lowers the water level.

2. Watch the Water Level

   The water level must be below the top of the tank's overflow tube. Continue adjusting as needed to get the appropriate water level.

How to Adjust a Float-Cup Fill Valve

The float-cup fill valve is the current standard design 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 plastic screw mechanism or a metal spring clip to a thin metal rod that controls the fill valve.

1. Find the Plastic Mechanism

   On some float cup valves, there is a plastic screw mechanism you can turn to raise or lower the float. Find this mechanism and turn it to raise or lower the float.
   

2. Slide the Float up or Down

   To lower the water level, slide the float down on the actuating rod. To raise the water level, slide the float up on the rod.

3. Watch the Water Level

   The water level should be about 1 inch below the top of the overflow tube and the critical level mark on the fill valve.

   Tip

   Some float cup valves use a metal spring clip. To adjust the water level, pinch both ends of the metal spring clip and raise or lower the float. Slide the float down on the actuating rod and then release the spring clip to lower the water level. To raise the water level, slide the float up on the rod and release the clip.

How to Adjust an Internal Float Fill Valve

One relatively new type of fill valve, sometimes marketed as 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 as a quieter valve with more precise shut-off. 

1. Twist the Top Head

   Twist the top head of the fill valve counterclockwise to unlock it.

2. Move the Valve Up or Down

   To lower the water level with this type of valve, move the entire head of the fill valve down. To raise the level of the water in the tank, raise the entire head of the fill valve up.

3. Twist the Top Head Back into Place

   Twist the head clockwise to lock it into place again. 

How to Adjust a Floatless or Pressure-Activated Fill Valve

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 underwater and can sense the water level based on pressure.

1. Turn the Adjustment Screw Clockwise or Counterclockwise

   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.

2. Watch the Water Level

   The water level must be below the top of the tank's overflow tube. Continue adjusting until you get the desired water level.

Tips for Tanks That Won't 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 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.