How to Fix a Running Toilet
Diagnose and repair a constantly running toilet by inspecting water levels, replacing a worn flapper valve, and adjusting the fill valve assembly.
- Read the tools, materials, safety notes, and steps below for free.
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🧰 Required Tools & Equipment
- ✓ Tongue-and-groove pliers
- ✓ Adjustable wrench
- ✓ Sponge
- ✓ Small bucket
- ✓ Flathead screwdriver
📦 Materials & Supplies
- ✓ Replacement toilet flapper
- ✓ Universal toilet fill valve kit
- ✓ Absorbent rags or towels
- ✓ Nitrile gloves
⚠️ Safety Checkpoints & Warnings
- • Turn the angle stop valve clockwise until fully hand-tight to prevent pressurized water leaks before disassembly.
- • Handle the heavy porcelain tank lid with both hands and place it flat on a carpeted or towel-lined floor away from the work area.
- • Never over-tighten plastic nuts onto porcelain; hand-tight plus a quarter turn with pliers prevents cracking the tank.
📋 Step-by-Step Guide (6 Steps)
Diagnose the Cause Inside the Tank
Carefully lift off the tank lid and set it safely on a flat, padded surface. Look inside while the toilet is running to check if water is spilling over the open top of the overflow tube or if the water level is low while the fill valve continues hissing. Push down gently on the flapper with your finger to see if the hissing immediately stops.
- • Tank lid removed and resting safely on towels on the floor.
- • Clear view of water line relative to the top edge of the vertical overflow tube.
- • Immediately replacing the fill valve when only the flapper is leaking.
- • Leaning the porcelain lid upright against a wall where it can slide and shatter.
Shut Off Water Supply and Drain the Tank
Locate the oval shut-off valve behind the toilet near the wall and turn it clockwise until it stops. Press and hold the flush lever down completely to empty the bulk of the water into the bowl. Use a large sponge to soak up the remaining 1-2 inches of standing water at the tank bottom, wringing it out into a bucket.
- • Angle stop knob turned fully clockwise.
- • Bottom of the porcelain tank completely dry with no standing water around the drain hole.
- • Failing to sponge out residual water, causing water to dump onto the bathroom floor when unthreading the valve base.
- • Forcing a corroded or stuck angle stop with excessive wrench torque.
Replace the Worn Flapper
Unhook the lift chain from the flush handle lever arm. Unclip the side ears of the old flapper from the hinge pins at the base of the overflow pipe and discard it. Snap the new flapper's mounting ears onto the pins and reattach the chain to the handle arm, leaving roughly 1/2 inch of slack.
- • New rubber flapper seated flat and centered directly over the drain opening.
- • Chain hanging with a slight curve, not pulled taut and not drooping into the drain hole.
- • Leaving the chain too tight, which holds the flapper slightly cracked open.
- • Leaving the chain too loose, causing it to slip underneath the flapper seal when dropped.
Replace the Fill Valve (If Needed)
Place a bucket underneath the water supply connection at the bottom-left exterior of the tank. Use an adjustable wrench to unscrew the water supply line coupling nut, then unthread the large plastic mounting nut securing the old fill valve to the tank bottom. Lift the old fill valve assembly out from inside the tank, position the new valve with its rubber sealing washer at the bottom, and hand-tighten the mounting nut underneath.
- • New fill valve standing vertical inside the tank without touching the tank walls.
- • Mounting nut firmly tightened against the underside of the tank ceramic with the rubber shank washer compressed inside.
- • Using pliers to overtighten the bottom plastic nut, which deforms the seal or cracks the porcelain.
- • Installing the critical rubber seal on the outside of the tank instead of the inside.
Connect Refill Tube and Supply Line
Clip the small flexible refill tube onto the top of the overflow pipe, directing water down into the tube rather than letting it spray into the open tank. Reconnect the braided water supply hose to the bottom threads of the new fill valve and hand-tighten the plastic nut securely. Turn the wall angle stop valve counterclockwise slowly to restore water flow.
- • Refill tube securely clipped to the vertical overflow pipe with water aimed down into the opening.
- • Water filling smoothly with zero leaks around the bottom supply connection.
- • Shoving the refill hose too far down the overflow pipe below the tank water line, creating a siphon.
- • Cross-threading the plastic supply line nut.
Calibrate Water Level and Test Flush
Allow the tank to fill until the valve shuts off automatically. Check that the final water surface settles approximately 1/2 to 1 inch below the rim of the overflow pipe or exactly on the tank's stamped water line mark. Turn the plastic adjustment screw on the float clockwise to lower the water level or counter-clockwise to raise it, then flush twice to verify a clean, silent shutoff.
- • Water stops filling crisp and completely 1/2 to 1 inch below the top of the overflow tube.
- • No hissing, trickling, or ripple movement in the tank or bowl after fill cycle ends.
- • Setting the float too high, causing continuous micro-overflow into the tube.
- • Forgetting to verify that the flapper seals instantly when released.
Credit: inspired by an original tutorial by Roger Wakefield Plumbing Education — watch the original on YouTube.
Don’t have everything?
- No Tongue-and-groove pliers? Standard slip-joint pliers with rubber-lined jaws
- No Sponge? Old terry cloth towel or microfiber cloth