How to Fix a Running Toilet Fill Valve: A Running Toilet How To Guide

Over the years, I’ve seen my fair share of problematic toilets, but a running toilet tends to be among the most common issues.

In particular, learning how to fix a running toilet fill valve is a skill that will no doubt serve you multiple times over.

It’s like a nagging cough that just doesn’t quit. You can choose to ignore it, but it doesn’t do you any good. It wastes water, racks up your water bill, and is a downright annoyance.

Are you having toilet fill valve problems?

Today, we’re going to tackle this how to fix a running toilet fill valve head-on – Its a quick fix for a running toilet.

Understanding Your Toilet Fill Valve

The fill valve is a crucial part of your toilet; it’s what keeps your toilet from turning into a miniature waterfall. It controls the amount of water in your tank after each flush, and when it’s not working correctly, you’ll hear that irksome running water sound.

These fill valves have been around since the 1950s, which means they’ve stood the test of time, but they’re not invincible.

How to fix a running toilet fill valve - Top view of a toilet

Identifying the Problem (is it really the fill valve?)

Determining whether the fill valve is truly the culprit of your running toilet isn’t always straightforward. While it’s true that an aging valve or debris caught in the valve are common causes, the problem could also be stemming from another part of the toilet.

Therefore, before looking to repair, it’s crucial to correctly diagnose the issue. Here’s how to identify if your fill valve is indeed at fault:

  • Continual Running: A classic symptom of a problematic fill valve is a toilet that continually runs. After you flush, the fill valve should refill the toilet tank and then shut off once it reaches a certain level. If the valve is faulty, it may fail to shut off, leading to continuous water flow.
  • Sounds After Flushing: If you hear your toilet making noise well after you’ve flushed, this might point to a fill valve issue. This could sound like a hissing or trickling noise as water continually flows into the tank.
  • Delayed Fill: Another sign of a faulty fill valve is if it takes an unusually long time for the tank to refill after a flush. This could mean that the valve isn’t opening properly to allow water into the tank.
  • Inconsistent Flushes: If your toilet sometimes flushes well and other times not so much, a malfunctioning fill valve could be to blame. This inconsistency is due to the valve failing to fill the tank to the correct level each time.

Inspecting the Fill Valve:

how to fix a running toilet fill valve - Flushing Mechanism Diagram
Flush toilet flushing mechanism

If the above symptoms align with what you’ve noticed, the next step is to visually inspect the fill valve. Shut off the water supply and flush the toilet to drain the tank. Then, take a look at the fill valve. Look for signs of wear, cracks, or debris lodged in the valve. If you see any visible damage, it’s highly likely your fill valve is the issue.

By correctly identifying the problem, you’ll ensure that your efforts to fix the issue will be successful and that you’re not unnecessarily replacing parts.

Once you’ve determined that the fill valve is at fault, you’re ready to move on to the repair process. If the fill valve is not at fault, you may want to check out our other article about how to fix a running toilet with a ball float or our article about how to fix a running toilet with a button flush.

Video Tutorial – How to Fix a Running Toilet Fill Valve

If you’re more of a visual learner, you may find this video helpful:

Tools and Materials Needed

Before embarking on this project, it’s important to assemble all the tools and materials needed. Having everything at hand can make the process smoother and prevent unnecessary interruptions. Here’s what you’ll need:

  1. Replacement Fill Valve: The core of this project is the replacement fill valve. For this guide, I utilized the 400H-002 fill valve from Fluidmaster, a trusted name in toilet repair parts. This model is designed to be compatible with a wide range of toilet models, making it a versatile choice.
  2. Bucket: As you’ll be dealing with water, having a bucket close by is absolutely necessary. This simple tool will catch any water that drips or spills during the process, saving you from mopping up a miniature indoor flood later.
  3. Sponge or Cloth: A sponge or a rag is essential for soaking up the remaining water in the toilet tank after you’ve turned off the water supply and flushed the toilet. An absorbent material like microfiber is an excellent choice.
  4. Adjustable Wrench: While most of the parts in this project are designed to be hand-tightened, an adjustable wrench can come in handy for removing the old fill valve or, if necessary, the water supply line.
  5. Tape Measure: A tape measure is needed to ensure proper placement and height of the fill valve. Proper measurement is key to a successful installation.
  6. Pencil: It might seem out of place, but a pencil plays a crucial role in this project. You’ll be using it to mark the water level in the toilet bowl, which is critical for fine-tuning the amount of water used per flush.
  7. Patience: Lastly, don’t underestimate the importance of patience. Like any DIY project, unexpected challenges may arise. Stay calm, take your time, and remember that the goal is a properly functioning toilet, not a race against the clock.

Step-by-Step Guide: Fixing a Running Toilet Fill Valve

Step 1: Turn off Water

Before you start working on the toilet, it’s essential to shut off the water supply to avoid flooding. Find the shut-off valve, which is usually located on the wall behind the toilet or somewhere close to it. The shut-off valve looks like a round or oval knob. Turn it clockwise to shut off the water.

If you have an older shut-off valve and it’s showing signs of wear, you might want to replace it with a SharkBite fitting. SharkBite fittings are reliable, easy to install, and they work with several types of pipes, including copper. Before you slide the SharkBite fitting onto the pipe, make sure the pipe is clean, free of burrs, and cut straight.

Step 2: Empty the Toilet Tank

After shutting off the water supply, flush your toilet to get rid of the water in the tank. Keep the lever pressed down to drain as much water as possible. When the water stops flowing, use a sponge or a cloth to absorb any remaining water in the tank. It’s a simple task, but be ready to rinse and wring out the sponge or cloth a few times.

Step 3: Remove the Old Fill Valve

Now, it’s time to remove the old fill valve. The first step is to unscrew the water supply line connected to it. Place a bucket or a towel underneath to catch any water still left in the line.

Once you’ve disconnected the water supply line, you’ll see a nut securing the fill valve to the bottom of the tank. Remove this nut, then detach the refill hose that connects the fill valve to the overflow pipe. With these connections removed, you can now lift the old fill valve straight out of its hole in the bottom of the tank.

Step 4: Install the New Fill Valve

Before you install the new fill valve, inspect the gasket to ensure it’s correctly positioned. If it looks good, place the new fill valve (I used the Fluidmaster 400H-002 model) into the hole previously occupied by the old valve.

Make sure the valve’s threaded shank goes through the hole at the bottom of the tank.

At this point, you need to measure the height from the top of the overflow pipe (flush valve) to the CL (Critical Level) mark on the fill valve, usually highlighted in a different color or indicated by the text “CL”. According to plumbing codes, this should be at least 3 inches. You can adjust the height of the 400H fill valve by twisting it.

Step 5: Secure the New Fill Valve

Next, secure the new fill valve. From the bottom of the tank, thread the fill valve nut onto the fill valve’s shank. Hand-tighten the nut.

No tools are required for this, and over-tightening with a tool could crack the tank. Make sure the fill valve is upright and that the refill hose attachment point is aiming toward the overflow pipe.

Step 6: Connect the Water Supply Line

With the new fill valve securely in place, it’s time to reconnect the water supply line. Hand-tighten the nut on the water supply line onto the threaded shank of the fill valve protruding from the bottom of the tank. As with the fill valve nut, this should be hand-tightened, and no tools are required.

Step 7: Turn the Water On and Check

Finally, it’s time to turn the water back on and check your work. Turn the shut-off valve counterclockwise to let water flow into the tank. Keep an eye on the water level as it rises. The

Troubleshooting Additional Problems

If your water level is off, don’t panic. The fill valve has a knob that can adjust the water height in the toilet tank. A clockwise turn raises the water height. Make sure to also check the water in the bowl.

Pour one gallon of water into the toilet bowl slowly to avoid accidentally flushing the toilet. The water line should be just above your pencil mark. If it’s above or below, adjust the height using the blue knob attached to the 400H.


Why does my fill valve keep running water?

If your fill valve keeps running water, it might be due to a float that’s set too high. When the float is too high, it fails to trigger the fill valve to shut off, causing continuous water flow. Alternatively, the issue could stem from a damaged or worn-out fill valve that’s unable to close properly, allowing water to keep flowing into the tank.

Why does my toilet fill valve run randomly?

Your toilet fill valve may run randomly due to a few reasons. Most commonly, this happens because of a faulty flapper that doesn’t seal correctly after flushing, causing the fill valve to trigger and refill the tank. Other causes could include a misadjusted float that doesn’t signal the valve to shut off properly or an old and worn-out fill valve that doesn’t function as it should.

Why does my toilet fill valve not shut off?

A fill valve might not shut off if it’s damaged, worn out, or set up incorrectly. The fill valve relies on a float to determine when to shut off. If the float is set too high or gets stuck, it will not signal the valve to close, causing the water to keep flowing. Additionally, if the fill valve is old or has a malfunction, it may not shut off, regardless of the float’s position.

How do you stop a toilet fill valve from running?

Stopping a toilet fill valve from running involves a few steps, largely depending on the root cause of the issue:
Check the Flapper: If the flapper is damaged or warped, it may not seal properly, causing the toilet to run. In this case, you’d need to replace the flapper.
Adjust the Float Height: If the float is set too high, the fill valve might keep running. Try adjusting the float to a lower level so that it can properly signal the fill valve to stop when the tank is full.
Clear Debris: Sometimes, debris can get stuck in the fill valve, causing it to run continuously. In this case, you’d need to turn off the water, flush the toilet to empty the tank, and then clean out any debris that might be stuck in the valve.
Replace the Fill Valve: If the fill valve is old or damaged, it may not be able to shut off properly, causing the toilet to run. In this case, you’d need to replace the fill valve.
Remember, before starting any of these fixes, it’s important to turn off the water supply to avoid flooding.

Final Thoughts


You’ve learned how to tackle a running toilet problem by replacing the fill valve!

By now, you should be more familiar with the parts of your toilet tank, know how to diagnose issues with the fill valve, and how to replace it if necessary.

Remember, DIY plumbing can be an excellent way to save money and gain useful skills. However, it’s essential to know your limits. If you’ve followed these steps and your toilet is still running, it might be time to call in a professional plumber.

In the meantime, keep this guide handy for your next toilet repair adventure. With patience, the right tools, and a little know-how, you’ll be surprised at what you can fix yourself. Happy plumbing!

References and Further Reading

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