Why Is My Toilet Leaking at the Base, and What Is the Right Fix?

Why is my toilet leaking at the base?

The bowl sits on a wax ring, and the wax ring sits on a closet flange screwed to the floor. Every flush sends a few gallons through that joint. When the seal is sound, nothing escapes. When it is not, a little water pushes out under the bowl each time, and a puddle forms at the base.

Most people notice the puddle before the cause. On a 1960s Valley tract house the trigger is usually a toilet that has started to rock on the tile. On a 1920s bungalow in Highland Park or Eagle Rock it is more often a corroded brass flange on a lead closet bend. Both leave the same wet ring on the floor.

A toilet leaking at the base has a broken seal, and the seal broke for a reason. Find the reason first, since a fresh wax ring on a cracked flange leaks again within months. Our toilet repair page covers running tanks and weak flushes; this guide stays on the floor.

How do I rule out condensation and a supply-line leak first?

Water on the floor around a toilet is not always coming from under it. Three other sources drip down the outside of the bowl and pool in the same spot. Ten minutes with a roll of paper towels sorts them out before anyone pulls a toilet.

1. Dry everything. Wipe the tank, the bowl, the supply line, the angle stop at the wall, and the floor. Lay a dry paper towel around the base.

2. Check for sweat. A tank of cold water fogs up in a warm, steamy bathroom, and the drops run down to the floor. A tank beaded with moisture means condensation, not a leak.

3. Feel the supply line and the tank bolts. Run a dry tissue along the braided line, the nut at the angle stop, the nut under the tank, and the two tank-to-bowl bolts. A damp tissue names the source.

4. Put food coloring in the tank. Ten drops, one flush, and a short wait. Colored water on the towel at the base came through the bowl and out the failed seal.

5. Flush and watch. A base leak shows within a minute or two of a flush and dries up between flushes. Condensation and a weeping supply nut keep the floor damp all day.

Condensation is rare in our dry climate, yet it happens in August in a bathroom with no fan, and near the coast where the air stays damp. A dripping tank bolt or supply nut is a tighten-or-replace fix. Only colored water at the base means the toilet has to come up.

What is actually leaking under the toilet?

Once the dye test points under the bowl, one of five things has failed, listed here in the order we find them.

• A failed wax ring. Wax does not reseal once the bowl shifts. A toilet reset on the old ring, or one that has rocked for a year, leaks with every flush.
• Loose or corroded closet bolts. The two bolts holding the bowl to the flange rust through, or the nuts back off. One side lifts a hair, and the seal opens.
• A rocking toilet on an uneven floor. Tile with a high spot, or a bowl set without shims, rocks every time someone sits down. Each rock works the wax.
• A cracked or corroded flange. Old cast-iron flanges rust until the bolt slots break away. The brass ring on a 1920s lead closet bend corrodes until nothing holds the bolt.
• A flange set too low. After a new tile floor the flange can sit half an inch below the finished surface. The wax never compresses, and the seal was thin from day one.

What you see, the likely cause, and the repair

Why does caulking the base make it worse?

Caulk feels like the obvious fix. The puddle stops, the bathroom looks finished, and the toilet moves less. The water has not stopped, though. It now runs under the bowl instead of out from it, into the flange screws and the subfloor.

We pull toilets in Van Nuys and Reseda that someone caulked shut years ago. The tile looks fine. Under it the plywood is black, the flange screws hold nothing, and only the caulk kept the bowl in place. A wax ring leak became a subfloor job.

The California Plumbing Code, which follows the Uniform Plumbing Code, does want the joint between a floor-mounted fixture and the floor made watertight. That rule assumes a sound seal underneath. The trade habit is to caulk the front and sides after the toilet sits tight and passes a flush test, and to leave a short gap at the back. A future leak then shows itself instead of hiding.

What does a proper repair involve?

The repair is a reset, done in an order that catches the real cause instead of covering it.

1. Close the angle stop, flush, and sponge the tank and bowl dry. Disconnect the supply line and unbolt the bowl. Rusted bolts get cut off with a small saw.

2. Lift the toilet onto a drop cloth and scrape every trace of old wax off the flange and the bowl horn. A rag stuffed in the drain keeps sewer gas out of the room.

3. Inspect the flange. Check the bolt slots, the ring, the screws into the floor, and the height against the finished tile. Press the subfloor around it for softness.

4. Repair or replace the flange. A broken slot takes a stainless repair ring. A corroded ring on a cast-iron or lead bend gets cut back for a new flange. A low flange gets an extender stack with sealant between layers.

5. Set the new ring, lower the bowl straight down, and snug the new bolts evenly. Shim any gap at the base until the bowl cannot rock, then trim the shims flush.

6. Reconnect the supply, flush several times, and check the base with a dry towel. Caulk the front and sides only after the joint has passed that test.

Lead closet bends deserve a word. Many pre-1950 houses in Bungalow Heaven, Silver Lake, and Boyle Heights still drain the toilet through a lead bend wiped onto a cast-iron stack, with a brass flange ring on top. Lead thins and splits under a flange that has rocked for decades. Replacing the bend is a plumbing alteration, so inside the City of Los Angeles it goes through LADBS; Burbank, Glendale, and Pasadena run their own permit counters. A reset or a wax ring swap is maintenance and needs no permit. A straight toilet swap is usually treated the same. The City of Los Angeles does issue an express permit for fixture replacement, though, so check with LADBS or ask us before the swap.

When does replacing the toilet make sense?

A reset saves a sound toilet. Some toilets are not worth setting back down, and the moment the bowl is up is the time to decide.

• A hairline crack at the base of the bowl or across the trapway. Cracks grow, and a bowl that lets go under load floods the room.
• A crack in the tank, or a tank someone patched with epoxy. Tanks hold water around the clock, so a slow crack becomes a flood while you are at work.
• An old high-volume tank. Anything from before the mid-1990s flushes three and a half gallons or more, while a new WaterSense model uses 1.28 or less. LADWP has run rebates on those swaps for years.
• Flange screws sitting in rotten wood. If the subfloor needs a patch, an old bowl with a scratched glaze and a weak flush rarely earns a second setting.
• Repeat clogs in the same bowl. A toilet that plugs every week with a clear drain line has a trapway problem no wax ring fixes.

Repair wins when one part failed and the porcelain is sound. Replacement wins when the bowl has a crack, the tank is a water hog, or the floor under it needs work anyway. Current ranges for both are on our toilet repair page, and we give the honest call on site rather than a push toward the bigger job.

When is a leaking toilet an emergency?

Most base leaks are a this-week repair. Close the angle stop, stop using that toilet, and book the reset. Three situations change that.

• Sewage on the floor. Water that comes out under the bowl after a flush is wastewater, not tap water. If it is brown, smells, or carries solids, the room needs a cleanup as well as a plumber.
• More than one fixture backing up. Water rising at the base while the tub or shower gurgles means the main drain has a blockage. The seal is the weakest point, so the backup exits there first. Stop running water anywhere in the house.
• Water reaching the ceiling below. A stain, a sag, or dripping from a light fixture under an upstairs bathroom means water has soaked through the subfloor. Cut power to that circuit at the panel if the fixture is wet.

In those cases call our emergency plumber line at (818) 421-5290. A live person answers 24/7, and a backup gets a drain machine, and a camera if needed, before anyone resets the toilet. A+ Electric & Plumbing is a licensed electrician and plumber serving Los Angeles and the San Fernando Valley, and a wet ceiling with a light fixture in it is exactly why both licenses ride on the same truck. One crew dries out the wiring and resets the toilet, with no second contractor to schedule and no finger-pointing.

What damage does a slow leak do to floors and health?

The water that leaves a failed seal is bowl water. It carries whatever went down with the last flush, and it soaks into whatever sits under the tile. Plywood swells and delaminates. Particleboard underlayment, common in 1970s and 1980s Valley remodels, turns to mush. The diagonal 1x6 sheathing under a 1920s bungalow rots along the grain.

Rot feeds the leak. Flange screws lose their grip in soft wood, the flange lifts, the toilet rocks more, and the seal opens wider. Mold gets going in damp wood within about two days. In a raised-foundation house the crawlspace under the bathroom takes the water; in a slab house it spreads sideways under the tile and shows up as dark grout two feet away.

If the floor feels soft, the grout has darkened, or a sour smell hangs in the bathroom with the toilet dry, water has run under there for a while. Our leak detection tools show how far it went, with a moisture meter on the floor and a thermal camera on the ceiling below. From there the Los Angeles plumbing team can scope the flange, the subfloor, and the drain in one visit. If you would rather start with a call to a licensed electrician and plumber in Los Angeles, that works too.

Frequently asked questions