A toilet that runs constantly — water trickling into the bowl between flushes, a hissing sound from the tank, the fill valve cycling on and off every few minutes — wastes a surprising amount of water. A running toilet can add 200 gallons or more to your daily water use, depending on the severity, which in Santa Cruz means a noticeable jump in your bill.
The good news is that most running toilets have a simple cause, a cheap fix, and are entirely manageable as a DIY repair. Here’s how to diagnose what’s wrong and what to do about it.
How a Toilet Tank Works
Understanding the basic mechanism makes diagnosis much easier.
When you flush, the flapper (a rubber seal at the bottom of the tank) lifts, allowing water to rush from the tank into the bowl. As the tank empties, the float — a ball or cylinder attached to the fill valve — drops with the water level and triggers the fill valve to open, refilling the tank. When the water reaches the correct level, the float rises and shuts the fill valve off. The overflow tube in the center of the tank is a safety drain — if the water level rises too high, water runs down the overflow tube into the bowl rather than flooding the floor.
A running toilet means water is moving from the tank to the bowl (or down the overflow tube) when it shouldn’t be. It’s almost always caused by one of three components: the flapper, the fill valve, or the float adjustment.
Step 1: Figure Out Where the Water Is Going
Remove the tank lid and set it somewhere safe. Watch the inside of the tank while the toilet is running.
Is water running down the overflow tube? The overflow tube is the tall open pipe in the center of the tank. If water is flowing into it, the water level is set too high and the fill valve isn’t shutting off properly. The fix is adjusting the float (see below).
Is the water level below the top of the overflow tube? Add a few drops of food coloring to the tank water and wait 10–15 minutes without flushing. Check the bowl — if the colored water has migrated into the bowl, the flapper is leaking. The fix is replacing the flapper (see below).
Is the fill valve running on and off periodically even when the tank is full? This points to a faulty fill valve that isn’t sealing properly when it shuts off, allowing the tank to slowly lose water and triggering brief refill cycles. The fix is replacing the fill valve.
Fix 1: Replacing the Flapper
The flapper is the single most common cause of a running toilet, and the repair takes about ten minutes. Flappers degrade over time — the rubber hardens and warps, the seal fails, and water slowly seeps past it into the bowl.
What you’ll need: A replacement flapper (matching your toilet brand and model, or a universal fit — take the old one to the hardware store to match it), and about ten minutes.
- Shut off the water supply valve behind the toilet. Flush to empty the tank.
- Unhook the flapper chain from the flush handle arm (note the chain length — you’ll reconnect it the same way).
- Remove the old flapper by unclipping the ears from the overflow tube posts or pulling it straight off, depending on your toilet model.
- Snap the new flapper onto the overflow tube posts, reconnect the chain. There should be about half an inch of slack in the chain — too much slack and the flapper won’t lift fully on flush; too little and it won’t seat properly and will keep running.
- Turn the water back on, let the tank fill, and observe. The running should stop once the tank fills and the flapper is fully seated.
Flappers cost $5–$15. If yours has been in place for more than 5 years, it’s due for replacement regardless of whether it’s causing an obvious problem yet.
Fix 2: Adjusting the Float
If water is running into the overflow tube, the tank is overfilling — the fill valve isn’t shutting off at the right water level. The water level should be about an inch below the top of the overflow tube.
How you adjust the float depends on the type:
Ball float (older toilets): A large plastic ball on a metal or plastic arm extending from the fill valve. Bend the arm slightly downward, or turn the adjustment screw at the fill valve end of the arm clockwise, to lower the shutoff level. The goal is for the float to trigger shutoff before water reaches the overflow tube.
Cylinder float (modern toilets): A cylinder that slides up and down the fill valve shaft. Look for a clip or adjustment screw on the fill valve — sliding the clip down or turning the screw lowers the water level at shutoff.
After adjusting, flush and observe the refill. The water should stop at least an inch below the top of the overflow tube. Adjust again if needed.
Fix 3: Replacing the Fill Valve
If the fill valve is running periodically, even when the tank is full — not an overflow tube issue, just intermittent cycling — the valve itself is faulty and needs replacement. Fill valves are also worth replacing if the toilet is making a foghorn or vibrating noise during refill, or if the refill takes noticeably longer than it used to.
Fill valve replacement is a slightly more involved DIY job, but still manageable:
What you’ll need: A replacement fill valve (Fluidmaster 400A or similar universal replacement fits most toilets), an adjustable wrench, a bucket, and a towel.
- Shut off the supply valve. Flush to empty the tank. Use a sponge or towel to remove remaining water from the tank bottom.
- Disconnect the supply line from the bottom of the tank (have the bucket ready — a little water will come out).
- Unscrew the locknut holding the fill valve in place from underneath the tank and lift the old valve out.
- Insert the new fill valve, following the manufacturer’s instructions for setting the height. Hand-tighten the locknut from underneath, then a quarter turn with a wrench. Don’t overtighten — you’re threading into a plastic nut against a plastic tank.
- Reconnect the refill tube (the small tube running from the fill valve to the overflow tube) and the supply line.
- Turn the water on slowly, let the tank fill, and check for leaks at the supply line connection and the fill valve base.
- Adjust the water level per the fill valve instructions — most have a clear marking for the correct setting.
A fill valve replacement costs $10–$20 for the part.
When It’s Not One of These Three Things
The flapper, float, and fill valve cover the majority of running toilet problems. But occasionally the issue is elsewhere:
Cracked overflow tube. If the overflow tube is cracked, water can seep through the crack into the bowl even with the water level set correctly. Replacing the overflow tube means removing the flush valve assembly — a more involved repair that most homeowners hand off to a plumber.
Worn flush valve seat. The seat at the base of the overflow tube (where the flapper seals against) can develop mineral deposits or pitting over time, preventing a proper seal even with a new flapper. A plumber can resurface or replace the flush valve.
Toilet internals are simply old. If a toilet has had multiple repairs and keeps developing new issues, replacing the entire flush mechanism — fill valve, flapper, and flush valve as a kit — is sometimes more economical than chasing individual failures. Complete rebuild kits cost $15–$30 at hardware stores.
The Water Waste Adds Up
Santa Cruz Water has a tiered rate structure — water use above the base allotment is charged at progressively higher rates. A running toilet that leaks 200 gallons a day adds roughly 6,000 gallons a month to your usage, which at higher tier rates can add $30–$60 or more to a monthly bill. A $10 flapper and ten minutes of work pays for itself immediately.
When to Call a Plumber
Running toilet repairs are among the most DIY-friendly plumbing tasks. Call a plumber when:
- You’ve replaced the flapper and fill valve, and the toilet still runs
- There’s water on the floor around the base of the toilet — this is a wax ring or supply line issue, not a tank issue
- The toilet rocks when you sit on it (loose or damaged floor bolts)
- You hear a hissing or running sound, but the tank appears normal — could indicate a crack in the tank or bowl
- The toilet is more than 20 years old and has had repeated issues — replacement may make more sense than another repair
Eco-Flow Plumbing Inc. handles toilet repairs throughout Santa Cruz, Live Oak, Aptos, Capitola, Soquel, Scotts Valley, Seabright, Felton, Boulder Creek, and Watsonville.
Contact Eco-Flow Plumbing if you need help. Or call directly: (831) 818-6331.
