How to Replace a Toilet Fill Valve

How to Replace a Toilet Fill Valve

Replacing a toilet fill valve is one of the most effective toilet repairs you can do — it fixes running toilets, noisy refills, and slow tank filling. The whole job takes under 30 minutes and costs under $20.

What You Need

• 👉 Fill valve and flapper repair kit — replace both at once for a complete fix
• Adjustable pliers or wrench
• Sponge and bucket
• PTFE thread seal tape for supply line reconnection
• Towel for the floor

Step-by-Step: Replace the Fill Valve

Step 1: Turn off the water supply.
Turn the shut-off valve clockwise until it stops. It's located on the wall behind or beside the toilet.

Step 2: Flush and drain the tank.
Flush the toilet to empty the tank. Use a sponge to remove the remaining water — the less water in the tank, the less mess when you remove the fill valve.

Step 3: Disconnect the supply line.
Unscrew the supply line from the bottom of the tank (counterclockwise). Have a towel ready for drips.

Step 4: Remove the old fill valve.
From below the tank, unscrew the fill valve locknut counterclockwise. You can usually do this by hand — use pliers if it's tight. Pull the fill valve straight up and out of the tank.

Step 5: Set the height on the new fill valve.
Before installing, adjust the height of the new fill valve. The critical level (CL) mark on the valve should sit at least 1 inch above the top of the overflow tube. Twist the valve body to adjust height.

Step 6: Install the new fill valve.
Insert the fill valve into the tank opening. From below, hand-tighten the locknut clockwise — then snug with pliers (a quarter turn past hand-tight). Don't overtighten.

Step 7: Connect the refill tube.
Attach the small refill tube from the fill valve to the overflow tube using the angle adapter clip. The tube should point into the overflow tube but not go down inside it.

Step 8: Reconnect the supply line.
Wrap the supply line fitting threads with PTFE tape and reconnect to the tank bottom. Hand-tighten plus a quarter turn.

Step 9: Turn water back on and adjust.
Open the supply valve slowly. Let the tank fill. Check the water level — it should be 1 inch below the top of the overflow tube. Adjust by turning the adjustment screw on the fill valve (counterclockwise to lower, clockwise to raise).

Step 10: Test.
Flush several times. Check for leaks at the supply line connection and at the fill valve base. Listen for the fill valve to shut off completely when the tank is full.

Pro Tip: Replace the Flapper at the Same Time

Since you already have the tank lid off and the water turned off, replace the flapper too. The fill valve and flapper kit includes both — a complete toilet tune-up in one repair that prevents future running toilet issues.

Bottom Line

Replacing a toilet fill valve takes under 30 minutes and requires only basic tools. Turn off the water, remove the old valve, install the new one at the right height, reconnect everything, and test. Replace the flapper at the same time for a complete fix.