Running Toilet? An Easy 5-Minute Diagnosis and Parts Guide

A running toilet is one of those problems that is easy to ignore — until you see your water bill. A toilet that runs constantly can waste anywhere from 20 to 200 gallons of water per day, depending on the severity of the issue. That adds up fast, especially over a North Dakota winter when the last thing you want is an unexpected plumbing expense on top of everything else.
The good news is that most running toilets are caused by one of just a few common problems, and with five minutes and a little know-how, you can usually figure out exactly what is going on before you decide whether to fix it yourself or call a plumber.
At Precision, we have been solving plumbing problems for homeowners in Fargo, Grand Forks, and the surrounding areas for over 20 years. Here is our straightforward guide to diagnosing a running toilet, understanding the parts involved, and knowing when it makes sense to handle it yourself versus calling in a pro.

Step 1: Listen and Identify What Type of Running You Have

Not all running toilets are the same. Before you lift the tank lid, just listen for a moment. There are two main types:

Constant Running

The toilet sounds like it is always filling, a steady stream of water trickling into the bowl or tank that never stops. This usually means water is escaping somewhere it should not be.

Intermittent Running

The toilet randomly refills on its own, even though nobody flushed it. This is often called a “phantom flush” and is almost always caused by a slow leak from the tank into the bowl.
Both are wasteful and worth fixing, but they often point to different culprits.

Step 2: Remove the Tank Lid and Look Inside

Take the lid off your toilet tank and set it aside carefully; they crack easily. Now look inside. A properly functioning toilet tank should be quiet and filled with water up to about an inch below the top of the overflow tube.
Here is what to look for:

Is the water level too high?

If water is spilling into the overflow tube, the tall, open tube in the center of the tank, your float is set too high or is malfunctioning. Water is continuously draining into the bowl through the overflow tube, which is why you hear constant running.

Is the flapper sitting flat on the flush valve?

The flapper is the rubber seal at the bottom of the tank that lifts when you flush and drops back down to let the tank refill. If it is warped, worn, or has mineral buildup around it, water will slowly leak into the bowl. This is the most common cause of phantom flushing.

Is the fill valve running nonstop?

The fill valve is the mechanism on the side of the tank connected to the water supply line. If it keeps running even when the water level looks correct, the fill valve itself may be worn out.

The 3 Most Common Causes of a Running Toilet

1. Worn or Warped Flapper

The flapper is the number one cause of running toilets. These rubber components degrade over time — especially in areas with harder water like Fargo and Grand Forks, and eventually stop forming a tight seal.
How to test it: Put a few drops of food coloring in the tank. Wait 10 to 15 minutes without flushing. If color appears in the bowl, your flapper is leaking.
DIY difficulty: Easy. This is one of the most beginner-friendly plumbing repairs you can do.
Part cost: $5 to $15 at any hardware store. Make sure to bring your old flapper or your toilet’s brand and model number to get the right fit.
Time to replace: 10 to 15 minutes.

2. Float Set Too High or Faulty Float

The float is the device that tells your fill valve when to stop adding water to the tank. In older toilets, this is a ball float on an arm. In newer toilets, it is typically a cup float that slides along the fill valve. If the float is set too high or is waterlogged and no longer floating properly, the water level rises until it spills into the overflow tube — and the fill valve never gets the signal to stop.
How to test it: Watch the water level in the tank. If it is at or above the top of the overflow tube, your float needs adjustment.
DIY difficulty: Easy to moderate. Adjusting a ball float involves bending the arm slightly downward or adjusting a screw. Cup floats typically have an adjustment clip or screw on the fill valve.
Part cost: If the adjustment does not solve it and you need a new fill valve, parts run $10 to $30.
Time to replace: 20 to 30 minutes.

3. Faulty Fill Valve

If your float looks fine and your flapper is sealing properly, but the toilet is still running, the fill valve itself may be worn out. Fill valves have internal seals and diaphragms that wear down over time, causing them to run continuously or to cut off inconsistently.
How to test it: Lift the float arm or cup manually while the water is running. If the water stops, the float is the issue. If it does not stop, the fill valve is likely the culprit.
DIY difficulty: Moderate. Replacing a fill valve requires shutting off the water supply, draining the tank, and disconnecting the supply line. It is doable for a confident DIYer but has more steps than a flapper replacement.
Part cost: $10 to $35 for a quality replacement fill valve.
Time to replace: 30 to 45 minutes.

Toilet Parts Replacement Cost Summary

Please note: Repair costs vary based on toilet brand, accessibility, and the scope of work involved. Contact Precision for an accurate estimate specific to your situation.

DIY vs. Call a Plumber: How to Decide

Handle It Yourself If:

• The problem is a worn flapper, and you are comfortable with basic home repairs
• The float just needs a simple adjustment
• You have already shut off the water supply, and the repair is straightforward
• The toilet is a standard model with readily available replacement parts

Call Precision If:

• You have replaced the flapper, and the toilet is still running
• Water is leaking at the base of the toilet or around the supply line connections
• The toilet is older, and multiple components are failing at the same time
• You are not comfortable working with the water supply line
• The toilet rocks, has visible cracks, or has other issues beyond a running problem
• You have tried a DIY fix, and the problem keeps coming back

A running toilet that keeps coming back after a DIY fix is often a sign that more than one component is worn out, or that there is a less obvious issue like a cracked overflow tube or a flush valve seat that needs resurfacing. In those cases, a full toilet rebuild or replacement is often the most cost-effective long-term solution.

When a Running Toilet Becomes an Emergency

Most running toilets are annoying rather than urgent, but some situations warrant a same-day call to a plumber.
Call Precision right away if:

• Water is actively overflowing from the tank or bowl
• You notice water on the floor around the toilet
• The supply line connection is dripping or spraying
• You have shut off the water and cannot get it back on

Precision offers 24/7 emergency plumbing service in Fargo and Grand Forks. If you have a plumbing situation that cannot wait, call us anytime:
Fargo: 701-300-8505 | Grand Forks: 701-317-9274

One More Thing: Consider a Plumbing Membership

If your toilet is running, it might not be the only thing in your home that needs attention. Precision’s Annual Plumbing Care Agreement includes a whole-home plumbing inspection, guaranteed rates, and proactive maintenance designed to catch problems like this before they cost you more on your water bill or result in an emergency repair.
Plumbing issues are responsible for 29% of all homeowner insurance claims, with an average repair cost of $12,500. A small investment in annual maintenance goes a long way toward protecting your home.

Need a Hand With Your Running Toilet?

Whether you want a plumber to handle it start to finish or just need a second opinion after your own diagnosis, Precision is here to help. We serve homeowners throughout Fargo, West Fargo, Grand Forks, and the surrounding areas with honest, fast, and reliable plumbing service.
Schedule your service online or call us directly:
Fargo: 701-300-8505 | Grand Forks: 701-317-9274