How to Fix a Toilet Fill Valve

The fill valve controls water flow into the tank after flushing. When it fails, your toilet runs constantly, refills too slowly, makes noise, or won't shut off. Here's how to diagnose and fix it.

Signs of a Faulty Fill Valve

Toilet runs continuously after flushing
Water level in tank is too high (overflowing into overflow tube)
Toilet takes a very long time to refill
Hissing or whistling sound from the tank
Water level in tank is too low (weak flush)

Fix 1: Adjust the Water Level

Before replacing the fill valve, try adjusting the water level:

For a cup-style float (most modern toilets):

Find the adjustment screw or clip on the fill valve shaft
Turn the screw counterclockwise to lower the water level, clockwise to raise it
Target: water level should be 1 inch below the top of the overflow tube

For a ball float (older toilets):

Bend the float arm downward to lower the water level
Or turn the adjustment screw at the fill valve if present

Fix 2: Clean the Fill Valve

Debris and mineral buildup can cause the fill valve to malfunction:

Turn off the water supply
Flush to empty the tank
Hold a cup over the fill valve cap and turn the water back on briefly — this flushes debris out of the valve
Turn water off, reassemble, and test

Fix 3: Replace the Fill Valve

If adjusting and cleaning don't fix it, replace the fill valve:

👉 Fill valve and flapper repair kit — includes both parts for a complete toilet repair

Turn off the water supply valve (clockwise)
Flush to empty the tank, sponge out remaining water
Disconnect the supply line from the bottom of the tank
From below the tank, unscrew the fill valve locknut (counterclockwise)
Pull the old fill valve straight up and out
Insert the new fill valve — adjust the height so the critical level mark is 1 inch above the overflow tube top
Hand-tighten the locknut from below — snug plus a quarter turn with pliers
Connect the refill tube from the fill valve to the overflow tube
Reconnect the supply line
Turn water back on, let tank fill, adjust water level if needed
Flush several times and check for leaks

How to Set the Correct Water Level

After installing the new fill valve, adjust the water level:

The water should sit 1 inch below the top of the overflow tube
Too high: water flows into the overflow tube — toilet runs constantly
Too low: weak flush — may not clear the bowl completely

Bottom Line

A faulty fill valve is easy to replace in under 30 minutes. Try adjusting the float level first — if that doesn't fix it, replace the fill valve. The repair kit includes both the fill valve and flapper, making it a complete toilet tune-up in one go.

Back to blog