A running toilet is one of those problems that seems minor but costs real money. A toilet that runs continuously can waste 200 gallons of water per day — that's over $50/month added to your water bill. The good news is that most running toilet issues are caused by inexpensive parts that are relatively easy to diagnose. Here's how to figure out what's going on with yours.
How Your Toilet Works (30-Second Version)
Understanding the four main components inside the tank makes diagnosis much easier. The flapper is a rubber seal at the bottom of the tank that lifts when you flush, releasing water into the bowl, then drops back down to seal the tank. The fill valve refills the tank after each flush. The float (either a ball on an arm or a cylinder on the fill valve) tells the fill valve when to stop filling. The overflow tube is a tall tube in the center of the tank that prevents flooding if the water level gets too high — excess water flows down this tube and into the bowl.
Cause #1: Worn or Warped Flapper
This is the most common reason for a running toilet — and the easiest to fix. The flapper is made of rubber, and over time it warps, cracks, or gets coated with mineral deposits (especially common with Central Texas hard water). When the flapper doesn't seal completely, water slowly leaks from the tank into the bowl. The fill valve senses the dropping water level and keeps running to refill the tank.
The test: Drop a few drops of food coloring into the tank (not the bowl). Wait 15 minutes without flushing. If colored water appears in the bowl, the flapper isn't sealing.
The fix: Turn off the water supply valve (the knob behind the toilet, near the floor). Flush to empty the tank. Unhook the old flapper from the overflow tube and disconnect it from the flush lever chain. Take it to the hardware store to match the size. Install the new one — it just clips on. Turn the water back on. Total cost: $5–$10 for the flapper, 15 minutes of your time.
Cause #2: Float Set Too High
If the water level in the tank is above the top of the overflow tube, water constantly trickles into the tube and down into the bowl. This means the float — the mechanism that tells the fill valve when to stop — is set too high.
The test: Remove the tank lid and observe the water level. It should be about 1 inch below the top of the overflow tube. If water is flowing into the overflow tube, the float is too high.
The fix: If you have a ball float (a plastic ball on a metal arm), gently bend the arm downward about half an inch. If you have a cylinder float (a cup-shaped float that slides up and down the fill valve), look for a small adjustment screw or clip on the side and lower the float by about half an inch. Flush and check the new water level.
Cause #3: Faulty Fill Valve
The fill valve controls the flow of water into the tank. When it wears out, it may run continuously, cycle on and off randomly, or make a hissing or whining sound. Fill valves typically last 5–7 years, less in areas with hard water.
The test: Lift the float all the way up by hand. If the water keeps running even with the float at the top, the fill valve is bad.
The fix: This is still a DIY-friendly repair, but it's a step up from replacing a flapper. Turn off the water and flush the tank. Disconnect the water supply line from the bottom of the fill valve. Unscrew the lock nut and remove the old valve. Install the new one (universal fill valves fit most toilets and cost $10–$20). Reconnect the supply line and adjust the water level. Total time: 20–30 minutes.
Cause #4: Cracked Overflow Tube
Less common, but it happens — especially on older toilets. If the overflow tube is cracked below the water line, water leaks through the crack and the fill valve runs to compensate. Inspect the tube for visible cracks or fractures.
The fix: The overflow tube is part of the flush valve assembly, which is the large plastic assembly bolted to the bottom of the tank. Replacing it requires removing the tank from the bowl — doable for a confident DIYer, but this is where most people call a plumber. Parts cost $15–$30, and a plumber will typically charge $150–$250 for this repair.
Cause #5: Worn Flush Valve Seat
The flush valve seat is the smooth surface where the flapper sits when the toilet isn't flushing. If this surface is corroded, pitted, or has mineral buildup, even a new flapper won't seal properly.
The test: Run your finger along the flush valve seat (the rim where the flapper rests). If it feels rough, pitted, or gritty, that's the problem.
The fix: You can try sanding the seat lightly with fine-grit sandpaper or emery cloth. If the corrosion is severe, the flush valve assembly needs to be replaced — same procedure as replacing the overflow tube.
When to Call a Plumber
Most running toilet issues are $5–$20 in parts and 15–30 minutes if you're comfortable with basic home repairs. But call a plumber if you've replaced the flapper and fill valve and the toilet still runs, there's water leaking from the base of the toilet onto the floor, the toilet rocks or feels unstable (the wax ring may need replacement), or you're not comfortable working with the water supply connection.
At Kimco, a toilet repair is a flat-rate service call. We'll diagnose the issue, fix it, and make sure everything is flushing and filling correctly before we leave. For homeowners in Lexington, Taylor, Elgin, Giddings, Bastrop, and our other Central Texas service areas — call (737) 260-7255.
Prevention Tips
Replace the flapper every 3–5 years proactively, even if it seems fine. They're cheap and they prevent the slow water waste that drives up your bill without you noticing. Don't use drop-in tank tablets — the chlorine in many tank cleaners deteriorates rubber components faster. Listen for phantom flushes — if your toilet occasionally sounds like it's refilling on its own (without anyone flushing), the flapper is starting to fail. Catch it early.