PLUMBING
Last updated: April 2026
The sound of a constantly running toilet isn’t just annoying — it’s one of the most wasteful plumbing problems you can have. A toilet that runs can waste up to 200 gallons of water per day.
Most of the time, a faulty fill valve is the culprit. The good news? Replacing a toilet fill valve is a straightforward DIY job that takes about 30 minutes and costs around $15-25.
Let’s get that toilet working properly again.
What Is a Fill Valve?
The fill valve is the mechanism inside your toilet tank that controls when water flows in to refill the bowl after a flush. When it goes bad, it either:
- Won’t shut off — water keeps running
- Won’t turn on — toilet won’t refill
- Leaks water into the bowl continuously
If your toilet runs constantly or makes a filling sound even when not in use, the fill valve likely needs replacing.
What You’ll Need
- Replacement fill valve (universal fits most toilets)
- Adjustable wrench
- Pliers
- Towels or rags
- Bucket
Check Current Price on Amazon – Fill Valve
Check Current Price on Amazon – Adjustable Wrench
Step-by-Step: Replace the Fill Valve
Step 1: Turn Off the Water
Locate the shut-off valve behind the toilet and turn it clockwise to shut off the water supply. Flush the toilet to drain the tank — use a sponge or towel to soak up any remaining water.
Step 2: Disconnect the Water Supply
Use your wrench to disconnect the water supply line from the bottom of the fill valve. Have a bucket ready to catch any water remaining in the line.
Step 3: Remove the Old Fill Valve
The fill valve is held in place by a mounting nut underneath the tank. Use your wrench to loosen and remove this nut. Then, lift the old fill valve out of the tank.
Step 4: Install the New Fill Valve
Place the new fill valve in the same position, making sure it’s centered. Tighten the mounting nut underneath the tank by hand, then snug it up with your wrench — don’t overtighten, which can crack the tank.
Step 5: Reconnect the Water Supply
Reattach the water supply line to the new fill valve. Tighten with your wrench.
Step 6: Turn On Water and Test
Turn the shut-off valve counterclockwise to restore water flow. Watch the tank fill — the water should stop at the fill line marked on the tank. If it overfills, adjust the float according to the manufacturer’s instructions.
Pro tip: Most universal fill valves have an adjustable float — slide it up or down to set the correct water level.
How to Adjust the Water Level
After installation, you may need to fine-tune the water level:
- Float too high — water runs into the overflow tube. Lower the float.
- Float too low — not enough water in the bowl after a flush. Raise the float.
Most fill valves have a simple clip or screw adjustment. Refer to the package instructions for your specific model.
Common Mistakes to Avoid
- Overtightening the nut — can crack the tank or valve
- Not centering the valve — causes uneven operation
- Forgetting to clean the tank — debris can affect the new valve’s performance
- Skipping the water test — always verify proper operation before finishing
If your toilet still runs after replacing the fill valve, the issue might be the flush valve or flapper. Check out our guide on How to Fix a Leaky Faucet (yes, the same principles apply to toilets too!) for more troubleshooting.
When to Call a Professional
Call a plumber if:
- The tank cracks during installation
- You can’t get the water level to adjust properly
- The toilet still runs after replacing the fill valve
- You notice water leaking from the base
Want more DIY plumbing tips? Our article on When to Call a Plumber vs DIY can help you decide what’s worth tackling yourself.
Conclusion
Replacing a toilet fill valve is one of the easiest plumbing fixes you can do. For under $30 and 30 minutes of your time, you can stop a running toilet and save up to 200 gallons of water daily.
Head to the hardware store, grab a universal fill valve, and silence that running toilet today.
This article was last updated April 2026.
Tags: replace toilet fill valve, running toilet, toilet repair, DIY plumbing, fix running toilet