If your toilet hisses, refills slowly, won't stop running, or makes a loud whine or "foghorn" noise after a flush, the fill valve is often to blame. It's the tall assembly on the left side of the tank that refills the tank and shuts the water off at the right level. Fill valves are inexpensive, and replacing one is a beginner-friendly job that usually takes 20 to 45 minutes with no special tools.
This guide covers how to tell if your fill valve is bad, what to buy, and how to remove the old valve and install a new one step by step.
Signs your fill valve needs replacing
- Water keeps running into the overflow tube, even after you lower the float.
- The tank refills very slowly or doesn't fill to the proper level.
- Hissing, whistling or vibration while the tank fills, or a faint hiss that never stops.
- Water leaks under the tank at the fill valve shank, where the supply line connects.
- An old ballcock valve (a float ball on a long arm). Modern float cup valves are quieter and easier to adjust.
Before you replace it, rule out the easy fixes. Make sure the water level is set about 1 inch below the top of the overflow tube, and that the refill tube is clipped above the water line, not pushed down inside the overflow tube. If the toilet refills on its own every few minutes but no water goes into the overflow tube, the problem is more likely the flapper. Our guide on how to fix a running toilet covers how to tell the difference.
Choosing a replacement fill valve
Most two-piece residential toilets accept a universal, height-adjustable fill valve. When you shop, check three things:
- Height range: Universal valves adjust to fit a wide range of tank heights. Check the product's listed range against your tank.
- Brand-specific designs: Some toilets, including certain TOTO, Kohler and American Standard models, use a specific fill valve or a specific refill setup. If you have one of these, an OEM replacement such as the TOTO TSU99A.XR fill valve assembly keeps the flush performing as designed.
- Anti-siphon (backflow) protection: Plumbing codes require toilet fill valves to have anti-siphon protection so tank water can't be drawn back into your drinking water. Look for a valve certified to the relevant ASSE/ASME standard, and install it with the critical level (CL) mark at the right height (see Step 4).
Popular universal choices include the Fluidmaster 400A universal fill valve and the Fluidmaster PRO45 toilet fill valve. Most fill valves include a new shank washer, locknut and refill tube. Many plumbers also replace the supply line at the same time, especially if it's older than about five years or has a plastic nut that looks cracked or brittle.
Tools and materials
- New fill valve (with its washer, locknut and refill tube)
- Adjustable wrench or groove-joint pliers
- Sponge, towel and a small bucket
- New toilet supply line (recommended)
- Gloves and a flashlight
Step-by-step: how to replace a toilet fill valve
Step 1: Shut off the water and drain the tank
Turn the supply valve behind the toilet clockwise until it stops. Flush and hold the handle down to empty as much water as possible. Use a sponge to soak up what's left in the bottom of the tank. Put a towel and a bucket under the supply connection to catch drips.
Step 2: Disconnect the supply line
Unscrew the coupling nut that connects the supply line to the bottom of the fill valve, under the tank. Most are hand-tight, but you may need pliers. Expect a little water to drip out.
Step 3: Remove the old fill valve
Unclip the refill tube from the overflow tube. Under the tank, loosen and remove the large locknut on the fill valve shank. Hold the valve body inside the tank with your other hand so it doesn't spin. Then lift the old valve straight out of the tank.
Wipe the tank hole clean and remove any old washer material or mineral buildup, so the new washer seals against a smooth surface.
Step 4: Set the height of the new valve
Most universal valves adjust by twisting the shaft or by sliding the body up or down before you install it. Follow the instructions in the package. As a general guide:
- The top of the valve, or its marked critical level (CL) line, should sit at least 1 inch above the top of the overflow tube. This is part of the anti-siphon protection.
- The valve shouldn't touch the tank lid when it's in place.
Step 5: Install the new valve
- Make sure the cone-shaped or flat shank washer is seated on the bottom of the valve, inside the tank, as the instructions show.
- Insert the shank through the tank hole.
- From below, thread on the locknut and tighten it hand-tight, then snug it about a half turn more with pliers while you hold the valve straight inside the tank. Don't over-tighten. Too much force can crack the porcelain or distort the washer.
- Make sure the float can move freely and doesn't rub against the tank wall, the flush valve or the flapper chain.
Step 6: Attach the refill tube
Connect one end of the refill tube to the nipple on the fill valve. Clip the other end to the top of the overflow tube using the angle adapter or clip supplied with the valve. The tube must stay above the top of the overflow tube. If it extends down inside the overflow tube below the water line, it can siphon water and keep the toilet running. If the tube is long, trim it with scissors so it doesn't kink.
Step 7: Reconnect the water supply
Thread the supply line onto the fill valve shank. Tighten plastic coupling nuts by hand only. For metal nuts, follow the line's instructions, usually hand-tight plus a small turn with a wrench. Slowly open the supply valve counterclockwise and let the tank fill.
Step 8: Adjust the water level and check for leaks
- Let the tank fill and watch where the valve shuts off. The water should stop about 1 inch below the top of the overflow tube, or at the water line mark inside the tank.
- Adjust the float using the screw, rod or clip on the valve, then flush and check again.
- Run a dry paper towel around the shank and supply connections under the tank. If it comes away damp, tighten slightly and recheck. Some valves take a few minutes to seal fully.
- Flush several times to confirm the tank refills, the bowl refills, and the valve shuts off fully and quietly.
Troubleshooting after installation
| Problem | What to check |
|---|---|
| Leak under the tank at the valve | Washer seated correctly? Locknut snug? Supply nut cross-threaded? |
| Valve won't shut off | Float rubbing the tank or chain; debris from the supply line in the valve; water level set too high |
| Slow fill | Supply valve not fully open; clogged supply line; debris in the valve cap or inlet |
| Weak flush after replacement | Water level set too low; refill tube not attached, so the bowl isn't refilling |
| Toilet still refills on its own | The flapper is leaking. Replace the flapper or check the flush valve seat |
Tip: After you replace a fill valve in an older home, debris that comes loose in the supply line can lodge in the new valve. If the valve hisses or won't shut off right after installation, shut off the water, remove the cap per the manufacturer's directions, and flush out the grit.
Safety notes
- Shut off the water first. If the supply valve behind the toilet won't close or starts leaking when you turn it, shut off the main water supply and consider having the stop valve replaced.
- Protect the porcelain. Set the tank lid on a towel on the floor. Hand-tighten plastic parts and avoid over-tightening anything that bears on the tank.
- Keep the anti-siphon protection intact. Install the valve at the height the manufacturer specifies, and don't cut or alter the valve body.
- Call a licensed plumber for a cracked tank, a corroded or seized supply valve, a leak at the floor, or any signs of water damage.
Find the right parts
Shop universal and brand-specific fill valves, flappers and supply parts in our toilet fill valves, flappers and repair parts collection. If you aren't sure which valve fits your toilet, send us the brand and model number from inside the tank and we'll help you match it.