Replacing a toilet fill valve

New product makes adjustments easier, eliminates corrosion concerns

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Do you have an older toilet that annoys you with the sound of water trickling after you flush, long after it should have shut off?

Have you tried adjusting and bending that big, frustrating, slimy rod and ball thingy and still can’t get things right?

Then it’s probably time for a new valve, and luckily this should prove to be one of the easier and less expensive projects on your to-do list.

Out with the old

Inside your toilet tank is a device called a ball cock. It’s a vertical valve on the left side of the tank, and it passes through a hole in the bottom of the tank itself, where it attaches to the incoming water line. When the toilet is flushed, water in the tank is released into the bowl to flush away waste, and the ball cock valve opens, allowing water to enter and refill the tank. A small tube coming out of the side of the valve enters a vertical tube called an overflow pipe, which is attached to the bowl. That allows a certain amount of the incoming water from the ball cock to be diverted into the bowl as well.

Older toilets utilize a float ball attached to a long arm, which floats on the surface of the water in the tank. As the water level rises, so does the float, until it reaches a preset level and shuts off the incoming water. Those float arms are notoriously cranky to adjust, and the older style of ball cock valves can get gummed up with sediment and other gunk over the years, leading to noisy operation and, worse yet, water-wasting leakage into the bowl because the valve never truly shuts itself off.

The solution is to replace the old-style ball cock valve with a newer one, such as Fluidmaster’s 400A Fill Valve. Fluidmaster has replaced the float ball and arm with a float cup that rides up and down on the valve itself, so it’s a lot easier to adjust. It’s also all plastic, so corrosion isn’t a factor, and it tends to maintain itself in the position where you set it.

Replacement is very straightforward

I recently had to replace a couple of these at my own house. The box said it was a 15-minute operation. The first one took a bit longer than that, due to a leaky water line that wasn’t the valve’s fault, and I got the second one changed in less than 10 minutes, so the average was right on. I will say that their instructions are some of the best I’ve seen.

To begin, shut the water to the toilet, then flush it to get most of the water out of the tank. After that, it’s bail-out time. Use a small can or whatever’s handy to scoop out as much remaining water as possible, then sop up what’s left with a sponge or a towel. It doesn’t need to be bone dry.

Now, unscrew the water line where it attaches to the bottom of the old ball cock (below the tank, on the left side), then loosen the big nut that holds the old ball cock in place. Take care not to damage the porcelain tank – advice that holds true throughout this process. Remove the old ball cock and discard it.

There are some parts packed in the Fluidmaster kit that you need to separate from one another; the instructions clearly explain how. One of those parts is a rubber washer, which you need to place over the end of the new valve before placing the valve temporarily into the hole in the tank.

Now comes a simple adjustment. On the side of the valve is a mark labeled "C.L.," which stands for critical level. Basically, it’s a guide to help you with where the water level needs to be so that the valve operates correctly. As the instructions explain, you’re going to want the C.L. mark to be at least 1 inch above the top of the overflow pipe. To achieve that, simply wind the adjustable valve stem clockwise or counterclockwise into the valve body, then measure from the overflow pipe to the mark until you have the measurement you want (in the "tools needed" part of the instructions, they neglect to mention you should also have a ruler or a tape measure, but that’s no big deal).

Once you have the dimensions correct, you can install the valve. Hold it in place so that the refill tube outlet is facing the overflow pipe and the float cup isn’t contacting the side of the tank anywhere, then press down to seat the washer and secure the valve in place with the provided lock nut. You’re instructed not to use tools on the lock nut, and that’s good advice; hand pressure is enough to get a watertight seal against the washer, and anything more risks cracking the tank.

Now, reconnect your water line to the bottom of the new valve. The instructions clearly cover four different types of water lines. New washers are provided where needed.

Next, connect the new refill tube between the valve and the overflow pipe, using the angle adapter fitting and clip that’s provided in the kit; you may need to trim the tube to the proper length so that it doesn’t kink, which is easily done with a pair of scissors.

To clear the valve of any possible sediment, you need to remove the cap from the top of the valve and flush it out. This is done by simply rotating the cap 1/8 of a turn counterclockwise, and it will unsnap and pop right off. Place a can or other container over the top of the valve to contain the water, then slowly turn the water valve back on. Water will shoot out of the top of the valve, clearing out any sediment. Repeat this a couple of times, then leave the water valve off.

Replace the cap on the valve by pressing down and turning 1/8 turn clockwise until it snaps back in place, then turn the water valve back on. The tank will now fill with water. Watch the level of the water in the tank. Your toilet should have a mark inside the tank indicating the ideal water level. If it doesn’t, you’ll want to shoot for a level that’s about 1/2 inch to 1 inch below the top of the overflow pipe. If the water level is too high or too low, simply turn the adjustment rod on the side of the valve to raise or lower the float cup, which will change the water level; you may need to flush the toilet a couple of times to finalize the adjustments.

Fluidmaster valves and other replacement toilet parts can be found at home centers, hardware stores and a variety of other retailers, as well as online through retailers such as


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