Fluidmaster Fill Valve Leaking From Top: How You Can Fix It

A Fluidmaster fill valve, also known as a refill valve or ballcock, is a mechanism that regulates how much water is in a tank. If the fill valve on your toilet isn’t working, water will continue to run, and you could end up with a higher bill than usual. 

I know from experience that a leaking toilet fill valve can happen due to several problems. These include mineral deposits and damaged parts. Let’s look at what might cause a Fluidmaster fill valve to leak from the top and how to fix it.

Toilet Fill Valve Leak Causes

When the flush valve on your toilet is not working and you don’t know how to fix or replace it, you can troubleshoot with a few simple steps.

The most common reason for a water tank fill valve leaking is the loosening of the lock nut. Other causes include mineral deposits, damage to the tank or valves, and clogging from scale buildup.

Let’s look at all four problems to find out which one is causing the fill valve leak.

Loose Lock Nut

If it takes a long time for your toilet to fill, then it stops suddenly and water continues to flow through to the overflow tube, you may have a leaking fill valve. If the flush rod has loose threats at either end, then it’s a sign that the lock nut has become loose.

A common cause of leaking toilet fill valves is loose lock nuts. When it becomes too loose, water seeps out from under it.

Clogged Fill Valve

If you hear water running in the drain or find puddles of water around the base of your toilet, the fill valve inside the tank may have become blocked.

Although clean water flows into and out of a freshwater tank directly from your supply, calcium and mineral debris can build up at the base of the tank, blocking water flow.

If the fill valve becomes clogged, no water can enter the tank. This prevents a flush from refilling with enough water to replace what was used in flushing.

When the fill valve is clogged, excess pressure can cause water to spill over an overflow pipe. Water leaking from the tank may puddle around your toilet base or seep onto floors and surfaces below.

Mineral Deposits

If you hear that the water keeps running and the toilet valve won’t shut off, it may lead to other problems. If your water supply contains high levels of calcium, those mineral deposits accumulate on internal parts after time.

Because these minerals build up, they eventually interfere with the seal of a valve, causing it to leak.

Looking at the inner workings of a tank, you should be able to see if any deposits have built up. The tank may appear dirty and the water might not be clear.

Damaged or Old Fill Valve

Toilet fill valves often last for about 5 years, though this is dependent on the quality of the valve itself as well as several other factors. 

For example, how often it’s flushed and whether or not your home water is hard can both play a role in determining its lifespan—just like any other type of fixture that receives constant use (and exposure to liquids) will eventually begin to wear down over time.

As a short-term solution, repairing the toilet fill valve will not address issues that arise when a new fill valve is needed.

How To Fix a Toilet Fill Valve Leak

Toilets have fill valves that help to maintain the water level and prevent overflow. If a fill valve is leaking, there are steps you can take to fix it yourself and stop wasting water. 

Before doing any work, turn the water off at its shutoff valve. If the shutoff valve doesn’t work, replace it before moving forward with any of these steps.

Replace or Tighten the Lock Nut

Use a wrench to tighten the armature’s lock nut. When tightening the lock nut, be careful not to use too much force. If the lock nut won’t tighten, replace it with a new one.

Before turning on the water to test it, check the seals both inside and outside the tank. To avoid a leak, replace the seal and add rubber gaskets to both sides of the toilet tank.

Toilet Fill Valve Unclog

I find that the best way to clear the toilet fill valve is following these steps:

1. Remove the toilet lid and use channel locks to grip around the pipe. Turn the pipe around counterclockwise to detach it.
2. Disconnect the valve from the fill pipe by unscrewing all three pieces (float cup, ballcock, and plunger).
3. Remove the hose at the top of the overflow tube.
4. Remove any clogs from the fill valve using something like a straightened wire hanger. Force debris through the tube with force if you need to. Clean up any additional residue that has fallen to the base of the valve body.
5. Wash all components off with clean water before reassembly.
6. Reinstall and tighten the fill valve into the toilet tank snugly.
7. To adjust the level of water in the tank, turn the float cup until it floats at an appropriate height.

While you are unclogging the toilet fill valve, it’s a good idea to clean up mineral deposits in the tank as well.

Clean Mineral Deposits

To ensure that the toilet fill valve is clean, do the following:

1. To empty a full toilet, make sure that the water supply is off so that there is no more water that enters the bowl, then flush.
2. In a spray bottle, add one part vinegar to three parts water.
3. Once the toilet is empty, use a razor blade to remove any old sealant from the fill valve. Wipe it down with a clean cloth and spray it with the vinegar mixture.
4. Mix and apply a paste made of baking soda and water to any visible mineral deposits. Also, clean the fill-valve access ports. Use an old toothbrush or cotton swab for gentle application.
5. After letting it sit for at least 15 minutes, rinse the area with clean water.
6. Replace the fill valve in its original position. Turn on the water and flush.

The toilet tank should be cleaned at least once per year to prevent mineral deposits from building up and causing fill valve clogs.

Replace Fill Valve

If you’ve tried tightening or replacing the lock nut, unclogging, and cleaning the toilet valve, and it’s still leaking, the fill valve may need to be replaced. 

To take out and change an old fill valve, follow these steps:

1. Turn off the water supply, flush once to drain the tank completely, then unscrew the flush valve counterclockwise.
2. Replace any broken or cracked tubing under the toilet.
3. Twist the new fill valve onto the flush valve tube until it is secure.
4. Ensure that the overflow pipe isn’t above the critical level on the filter valve; cut the pipe shorter if necessary.
5. Reconnect the fill valve to the water supply pipe.
6. Reattach the fill tube to the overflow pipe’s open end and turn on the water supply.
7. Adjust the water level to about half an inch below the top of your tank.
8. Before flushing, turn on the faucet nearest the toilet to be sure no water is dripping from elsewhere.

Final Thoughts

There’s no reason to tolerate a leaking toilet. You can do lasting damage to your home if you leave an old and malfunctioning valve in your toilet. Review the reasons why your Fluidmaster fill valve may be leaking.  You should now have a better idea of whether you can repair it, or you need to replace it.

The good news is that even though this may seem like a big project at first glance, it isn’t all that difficult. Once you know what you need to do to fix it, you’re set!