How to Fix a Toilet That Keeps Running (DIY Guide)

A toilet that keeps running usually points to a warped flapper, a misadjusted float, or a failing fill valve. You can fix a toilet that keeps running in 15 minutes with basic hardware store parts. If the water won't stop, turn off the supply valve behind the base immediately.

Key takeaways

• A warped or mineral-crusted flapper is the most common cause of a running toilet.
• Hard water buildup prevents internal tank valves from sealing properly.
• A constantly running toilet can waste over 200 gallons of water daily.

Why does my toilet keep running intermittently?

When a toilet randomly starts and stops filling, plumbers call this a phantom flush. The tank is slowly losing water into the bowl. Once the water level drops low enough, the fill valve kicks on to replace it.

The culprit is almost always the flush valve seal. In Greater Sacramento, our municipal water supply contains high levels of dissolved minerals. This hard water leaves calcium and magnesium deposits on the rubber flapper inside your tank.

Over time, these deposits harden the rubber. The flapper loses its flexibility and can no longer form a watertight seal. Water seeps past the rigid rubber, draining the tank drop by drop.

Steps to fix a toilet that keeps running

Before you dismantle the tank, clear off the lid and set it flat on a towel. Toilet tank lids are fragile and expensive to replace.

1. Turn off the water supply. Locate the shutoff valve on the wall behind the toilet and turn it clockwise. If the valve is stuck, do not force it, as old valves can snap and flood your bathroom.
2. Inspect the flapper and chain. Flush the toilet to drain the tank and inspect the rubber flapper at the bottom. If it looks warped, feels brittle, or is coated in white scale, replace it. Ensure the chain connecting the flapper to the flush lever has exactly half an inch of slack.
3. Check the overflow tube. Turn the water back on and watch the tank fill. If water pours over the top of the open pipe in the center, your water level is too high.
4. Adjust the fill valve float. Locate the adjustment screw on top of the fill valve and turn it counterclockwise to lower the float. Flush again to verify the water stops filling about one inch below the top of the overflow tube.
5. Replace the fill valve. If you adjusted the float but the water still runs, the internal seals in the fill valve have failed. You will need to drain the tank completely, unscrew the supply line, and install a new fill valve kit.

Repair vs. Replace: When to call a professional

Most running toilets require simple, inexpensive parts. However, persistent leaks often hide deeper structural failures. If you replace the flapper and the tank still drains, you likely have a cracked flush valve or a failing tank-to-bowl gasket.

Consider a recent service call in Placer County. A homeowner replaced their flapper three times trying to stop a leak. The actual problem was a hairline crack in the overflow tube.

Water was bypassing the tank entirely and rotting the subfloor. This situation required professional toilet repair to pull the tank and rebuild the internal assembly.

Learning how to fix a toilet that keeps running is a straightforward job that saves significant water and money. Start with the flapper and float adjustments. If the fixture still runs, or if you spot water pooling around the base, shut off the supply immediately. For persistent issues, reach out through our contact page to schedule a service visit.

How much water does a running toilet waste?

A constantly running toilet can waste up to 200 gallons of water per day. Over a single month, this continuous flow can add hundreds of dollars to your utility bill and put unnecessary strain on local water resources.

Why does my toilet only run at night?

Toilets do not actually run only at night. Municipal water pressure often increases overnight when neighborhood usage drops. This pressure spike forces water past a weak fill valve, making the running sound noticeable when your house is quiet.

Can hard water cause my toilet to run?

Yes. The mineral-heavy water in Northern California leaves calcium deposits on rubber seals. These deposits stiffen the flapper and prevent it from creating a watertight seal against the flush valve, leading to constant leaks.