Your toilet only has a few parts that need to move or control the water flow. Among these components, the fill valve is a component failure point. The fill valve monitors the water level in the tank, refilling when necessary to keep the tank ready for the next flush. A faulty fill valve is a common suspect when your toilet won't stop running.

Unfortunately, many homeowners assume that the fill valve is the only reason that a toilet might keep running. This assumption can lead to an unnecessary replacement and a toilet frustratingly refusing to stop running. As it turns out, there are several reasons that your toilet may run all night, wasting water and keeping you awake.

What Causes Toilets to Run?

Most toilets use a separate tank and bowl connected by an opening at the tank's base. This opening allows water to flow from the tank to the bowl, traveling around the rim and through the openings at the top of the bowl. Inside the tank, a flapper keeps the water contained until you pull on the handle and allow water to flow into the bowl.

Since the fill valve determines when to refill the tank, the fill valve usually causes the tank to run. A faulty or misadjusted fill valve is the two most common causes of an endlessly running toilet. However, any water that leaks into the bowl from the tank will also cause the valve to run. Since the fill valve will detect the low water level, it will run continuously to compensate for the loss.

Why Do Toilet Tanks Leak?

A leak is most likely at fault for a running toilet if your fill valve works correctly and is properly adjusted. Toilets most commonly leak at the connection between the tank and bowl, and the flapper inside the tank is typically the failure point. These flappers can become hard or wear out, ultimately failing to make a good seal with the valve seat. Sediment can also prevent the flapper from sealing with the seat.

Internal failures can also occur. Most toilets contain a gasket to seal between the tank and the bowl. This gasket prevents water from leaking from the back of the tank but can also cause a slow drip into the bowl. In some cases, the ceramic on the toilet can physically crack, allowing water to leak from the tank directly into the bowl.

How Can You Fix Your Running Toilet?

"Replace the fill valve" is common advice, but it can lead to an unnecessary or counterproductive repair if you don't have the skills necessary to diagnose the problem. If you aren't sure why your toilet is running, contact a professional plumber to help you investigate the issue. An experienced plumber can check for problems with the flapper and o-ring, as well as physical damage to the toilet.

The good news is that cracks on toilet tanks are relatively rare, especially if your toilet isn't particularly old. In most cases where the fill valve isn't at fault, the problem will lie with one of the rubber components between the tank and the bowl. Replacing the affected component will stop the leak and save you from the frustration of an endlessly running toilet.

For more information on residential plumbing, contact a professional near you.