Replace a Toilet Fill Valve

Water running constantly. That thin whistle that keeps you awake at three in the morning. The toilet that never quite stops filling. These are the sounds of a dying fill valve, and they're costing you money with every flush. The fill valve is the vertical assembly inside your toilet tank that controls water flow after each flush. When it fails, your toilet either won't fill properly or won't stop filling at all. A new valve costs less than fifteen dollars and takes half an hour to install, making it one of the highest-return repairs in the house. This job requires no special skills and almost no tools. You're working with hand-tight connections and a simple compression fitting. The new valve will likely work better than the original even when the original was new, because fill valve design has improved considerably in the past decade. Modern valves are quieter, more reliable, and adjust without tools. Once you've done this repair, you'll wonder why you waited so long.

1. Stop the Water Flow. Turn the oval shutoff valve clockwise until it stops, usually a quarter turn. This valve sits on the water supply line below the tank, against the wall or floor. Flush the toilet and hold the handle down to drain as much water as possible. Use a sponge or old towel to soak up the remaining water in the bottom of the tank.
2. Free the Supply Line. Under the tank, locate where the supply line connects to the threaded shank of the fill valve. Use an adjustable wrench or slip-joint pliers to turn the coupling nut counterclockwise. Keep a towel handy for residual water in the line. Once disconnected, move the supply line out of your way.
3. Extract the Old Valve. Inside the tank, unclip or unscrew the refill tube from the overflow pipe. Under the tank, unscrew the plastic locknut that holds the fill valve in place by turning it counterclockwise. This nut is hand-tight and often has wings for grip. Lift the old valve straight up and out through the top of the tank.
4. Size Up the New Valve. Before installation, adjust the new fill valve so the top sits at least one inch above the overflow pipe. Most modern valves twist or have a release clip that lets you extend or compress the body. Measure while holding the valve in position inside the empty tank to get the height right.
5. Seat the New Valve. Insert the new valve through the mounting hole in the bottom of the tank. From underneath, thread the locknut onto the shank and hand-tighten clockwise until snug. The rubber gasket should compress slightly against the tank bottom. Inside the tank, clip the refill tube onto the overflow pipe, making sure it's secure and will direct water into the pipe opening.
6. Restore Water Flow. Thread the supply line coupling nut onto the threaded shank of the new valve by hand first, then tighten with pliers or a wrench. Snug is sufficient; overtightening brass fittings can strip threads. Make sure the connection is straight, not cross-threaded.
7. Verify No Leaks. Slowly turn the shutoff valve counterclockwise to restore water flow. Watch the connections under the tank for leaks while the tank fills. If water drips from either connection, turn off the water and tighten another quarter turn. Inside the tank, watch the water level rise and ensure the valve shuts off automatically.
8. Perfect the Water Level. The water should stop about one inch below the top of the overflow pipe. Most modern valves have an adjustment screw on top or a float cup that slides up and down the valve body. Turn the screw or squeeze the adjustment clip and move the float to raise or lower the shutoff point. Flush and verify the level stabilizes correctly.