How a Toilet Fill Valve Works

Last Updated on August 6, 2023 by toilethaven

What is a Toilet Fill Valve?

A toilet fill valve is a toilet tank part that refills the tank after every flush. It is connected to a water supply line from underneath the tank. The supply line is connected to the toilet shut-off valve, which on the other hand, is connected to the water supply pipes.

The toilet shut-off valve is the knob on the wall behind the toilet tank. It provides a way to isolate water flow to the toilet when you want to perform repairs on the toilet.

The toilet fill valve is also connected to the toilet float. A toilet float is a device that controls the opening and closing of the fill valve by moving up and down in the toilet tank.

Your toilet fill valve will either be connected to a float ball or a float cup. Float balls are more common with old toilet models. They have a round ball which is connected to the fill valve by a float arm. The float arm can either be metallic or plastic. These toilet floats are also called ballcocks.

On the other hand, a float cup is more compact and is the one you are likely to find in modern toilets. It is connected to the vertical body of the fill valve.

When a toilet tank is filling slowly or when noises are coming from the toilet after flushing the toilet, the problem is usually the fill valve.

How a Toilet Fill Valve Works

toilet diagram
  • Before flushing the toilet, the toilet tank is full of water. The fill valve is shut, and the toilet float is floating at the top of the tank.
  • When you push the flushing handle down, the toilet flapper is lifted off by a lift chain, and the water in the tank flows out and down to the bowl through the flush valve.
  • After releasing the flush handle, the lift chain slacks off. The toilet flapper falls back in position and seals the flush valve in preparation for the refill.
  • Since the toilet tank is empty, the toilet float, now at the bottom of the tank, prompts the fill valve to open.
  • Water starts to fill the tank through the fill valve.
  • As the water fills the tank, the toilet float moves up gradually.
  • When the toilet float reaches its set height, it stops and shuts off the fill valve. Water stops flowing into the tank, and the tank goes silent.
  • As the fill valve was refiling the tank, a small tube called the refill tube which is connected to the fill valve, was also sending a small amount of water down to the bowl via the overflow tube. This is the water you see at the bottom of the toilet bowl. It acts as a barrier preventing sewer gases from coming up to the bathroom. The overflow tube is the large tube in the middle of the tank. It sends excess water in the tank down to the bowl to prevent the tank from overflowing.

How to Adjust a Toilet Fill Valve

A toilet fill valve and the toilet float will determine the water level in the toilet tank. If the fill valve is not adjusted correctly, the water level in the tank will either be too low or too high. The water level in the toilet tank should be about 1 inch below the overflow tube.

If the water level in the tank is too low, your toilet will not have sufficient force during flushing, resulting in a weak flush where you will need to flush twice or more.

When the water level in the tank is too high, the water will start to flow down to the bowl via the overflow tube. You will therefore have a constantly refilling and running toilet.

Adjusting a toilet fill valve is easy. You will only need a screwdriver.

  • If you have a float ball, look at where the float arm is connected to the fill valve. You will find a screw. Using the screwdriver, turn the screw clockwise to lower the water level and counterclockwise to raise the water level.
  • If you have a float ball, look for a long plastic screw adjacent to the fill valve. Turn the screw clockwise to lower the water level and counterclockwise to raise the water level in the tank.

How Do I Know If My Toilet Fill Valve Is Bad?

  1. Toilet making a hissing/whistling sound – When the toilet fill valve is blocked and is not opening fully, the water forces its way through it. After flushing your toilet, it will make a hissing/whistling sound as it refills.
  2. Toilet running constantly – When your toilet fills valve seal is worn out, the fill valve will not shut even after the tank is full. It will continuously fill the tank. The excess water in the tank will be channeled down to the bowl via the overflow tube resulting in a constantly running toilet.
  3. Leaking supply line coupling – When you notice water leaking at the coupling that connects the supply line to the fill valve, it means the fill valve is blocked mostly by mineral deposits. You might also notice that the fill valve is taking too long to refill the tank or not refilling at all.

Can You Repair a Toilet Fill Valve?

Although it is possible to repair a toilet fill valve, replacing it is usually the best option. A fill valve is inexpensive and easy to replace on your own. If you would like to buy a good fill valve, here are the best ones.

In certain cases, fixing a fill valve makes sense. If you have a fairly new fill valve and suspect its seal is blocked by mineral deposits or other debris, you can surely fix that.

  • Turn off the water to the toilet by turning the shut-off valve clockwise.
  • Flush the toilet.
  • Hold the fill valve shank with one hand and turn the cap at the top 1/8 turn with your other hand. This is how to remove the cap.
  • Check for the presence of dirt on the seal.
  • Hold a cup inverted on top of the fill valve.
  • Turn on the water.
  • The water pressure will force all the dirt out, while the cup will prevent the water from splashing all over the bathroom.
  • When the valve is fully unblocked, put it back.
Float-cup toilet fill valve

If you need to replace a toilet feel valve, this is a detailed guide on how to go about it. Toilet fill valves are universal, so you don’t always have to buy one from your toilet manufacturer. Korky’s and Fluidmasters are some of the best universal toilet fill valves.