Why Does My Toilet Keep Running? Flapper or Fill Valve

A toilet that refills on its own, when nobody has touched the handle, comes down to one of two parts in the tank: the flapper or the fill valve. When we get this call, the first thing we do is lift the tank lid and look at what is happening inside. You can do the same, and a quick test will usually tell you which part has failed.

What makes a toilet run on its own?

Almost every time, it is a bad flapper or a bad fill valve. The fill valve is the part with the float on it, and it controls the water coming into the tank. A bad fill valve never shuts off, so water keeps flowing in.

A bad flapper shows up differently. You will see water slowly drizzling into the tank even though nobody flushed.

How do you tell a bad flapper from a bad fill valve?

Take the lid off the tank and lift the float on the fill valve by hand. Then watch what the water does.

The water stops: the fill valve is doing its job, and the flapper is the problem.

The water keeps coming in: the fill valve is bad. Even with the float held up, it will not shut off.

There is a second sign of a bad flapper. With the lid off, look for that slow drizzle of water into the tank. If you see it, the flapper is the part to replace.

These are the same simple checks we use on a service call to diagnose a running toilet, and any homeowner can run them.

Can I replace a toilet flapper myself?

Yes. Of the two repairs, the flapper is the simple one, and it is a good job to take on yourself. You never touch any of the pressurized lines on the water system. All of the work stays inside the tank.

Should I replace a fill valve myself?

Be more careful with this one, because a fill valve job can snowball into bigger problems. First you have to close the toilet's emergency shutoff valve. Then you unscrew the supply line. After that, the old fill valve comes out of the tank and the new one goes in.

The trouble is usually that shutoff valve. More often than not, an aged shutoff valve begins to leak as soon as you try to close it. Now a small repair has become an emergency, and you have to shut off the water to the whole house.

If you are not sure where your shutoff valves are, our emergency plumbing page explains how to find the valve at a fixture and the main shutoff for the house. If the shutoff under your toilet is old, think twice before you turn it.

Is a running toilet a big deal?

It is easy to shrug off. A running toilet looks like a small problem, but it means water is flowing day and night, nonstop, and all of it lands on your water bill. The longer it runs, the more you pay for water that does nothing for you.

What does a running toilet repair usually cost?

It depends on which part has failed. When we replace a flapper, expect roughly $185 to $265. A fill valve replacement runs roughly $250 to $375.

Where a fill valve job lands in that range comes down to the type of toilet you have and its flush valve.

When should you call a plumber?

Run the float test first. If it points to the flapper, you can most likely make the repair yourself.

If it points to the fill valve, take a look at the shutoff valve under the toilet before you do anything. If that valve is old, or it starts leaking when you turn it, stop there. Shut off the water to the house and call us at (909) 600-4561.

You can see everything else we handle on our services page.