Toilet Running: Triage and Repair
A commercial toilet or urinal that keeps running wastes thousands of gallons and often signals one worn part. Identify tank type versus flushometer before touching anything.
Last reviewed 2026-09-12 · General facility-maintenance information, not a substitute for site procedures, manufacturer instructions, codes, or qualified professional judgment.
Quick answer
Safety boundary
Likely causes
- Worn or misaligned flapper or flush valve seal (tank type)
- Fill valve not shutting off, or float set too high (tank type)
- Fouled or torn diaphragm kit in a flushometer
- Debris under the relief valve or seat causing continuous flow
- Handle or actuator sticking and holding the valve open
- Sensor flush valve solenoid or module fault, or low batteries
- Water pressure too high or supply stop partly closed
- Chain or lift wire length wrong after a prior repair
- Damaged vacuum breaker or worn tailpiece gasket
Symptom → cause → first move
Tank refills every few minutes with no flush
Check: Flapper seal and dye test in the tank
First move: Replace the flapper with the matching model, then retest
Water runs into the overflow tube constantly
Check: Fill valve shutoff and float setting
First move: Adjust the float, then replace the fill valve if it still will not shut off
Flushometer runs continuously after flushing
Check: Diaphragm kit, relief valve, and bypass orifice for debris
First move: Isolate water, rebuild with the correct kit for that valve model
Sensor valve cycles or runs on its own
Check: Battery or transformer, sensor range, and solenoid
First move: Replace batteries and clean the sensor window, then replace the solenoid module
What to check first
Bring these
- Flushometer wrench or smooth-jaw spud wrench
- Correct rebuild kit or flapper for the exact valve model
- Channel-lock pliers and screwdrivers
- Bucket, towels, and a wet/dry vacuum
- Nitrile gloves, safety glasses, and disinfectant
Before touching anything
- Immediate safety check: confirm the floor is not slick, the fixture is secure, and there is no sewage backup in the room
- Identify the valve manufacturer and model from the cover casting or label
- Verify the fixture stop closes fully and holds before you open anything
- Post an out-of-service sign and have the correct rebuild kit on hand
Step-by-step procedure
- 1Identify the flush technologyTank-type, manual diaphragm flushometer, piston flushometer, or sensor-operated. The repair path and parts are different for each.
- 2Confirm the run-on with a simple testFor tanks, add dye to the tank and watch the bowl. For flushometers, listen at the valve and watch the bowl water surface for continuous movement.
- 3Isolate the waterClose the fixture stop with a screwdriver or key. If the stop is seized, stop here and schedule a plumber rather than risk a break.
- 4Open and inspectFor a tank, inspect flapper, seat, fill valve, and chain length. For a flushometer, remove the cover and inspect the diaphragm, relief valve, and bypass orifice for grit and scale.
- 5Rebuild with matching partsInstall the manufacturer's kit for that exact model. Do not mix kits between brands or valve generations.
- 6Restore water slowly and testOpen the stop partway, check for leaks, then flush three times and confirm a clean shutoff and correct bowl level.
- 7Log the repairRecord fixture location, valve model, kit installed, and date so the next technician has the part number.
Routine fixes that make sense here
- Replace a flapper, fill valve, or lift chain in a tank-type toilet
- Rebuild a diaphragm or piston flushometer with the manufacturer's kit
- Clean the bypass orifice and seat of scale and grit
- Replace sensor-valve batteries and clean the sensor window
- Replace the handle assembly on a manual flushometer
- Adjust flush volume within the manufacturer's range
Write the model on the wall behind the valve
Preventive maintenance
- Add flushometer rebuilds to an annual or biennial PM cycle by fixture count
- Keep common rebuild kits and flappers stocked by valve model
- Log restroom fixture inspections monthly (Toolbox restroom checklist)
- Track water bills for step increases that signal silent run-on
- Replace sensor batteries on schedule instead of on failure
Stop and call a licensed professional when
- Fixture stop or supply that will not close or is corroded
- Water at the base of the toilet or a rocking fixture (possible failed closet flange or wax seal)
- Sewage backup, multiple fixtures affected, or suspected main line blockage
- Any repair that requires cutting or soldering piping outside your authorization
- Backflow preventer or vacuum breaker on a potable system needing certification
- Continuing high pressure or hammer that suggests a system pressure problem
Common mistakes
- Guessing the rebuild kit instead of reading the valve model
- Overtightening a spud coupling and cracking the connection
- Leaving the stop only partly open, which causes weak flushes later
- Ignoring a rocking fixture while chasing the run-on
- Skipping the three-flush verification test
FAQ
How much water does a running fixture waste?
A continuously running flushometer can waste hundreds of gallons a day. Treat run-on as urgent even when nobody complains.
Can I use a universal rebuild kit?
Prefer the manufacturer's kit for that exact valve model. Universal parts often cause weak flushes or repeat failures.