A sensor toilet that keeps flushing is usually seeing something that is not a user: a dirty lens, a stall door or wall inside its range, or weak electrical power. Some repeat flushes are by design, such as a courtesy flush or a timed 24-hour flush. A valve that never shuts off is a different fault.
Is it a repeat flush or a flush that never stops?
Watch one full cycle. If the valve finishes, goes quiet, then flushes again on its own, that is a sensor or power problem and this page applies. If the water keeps running through the bowl without a break, the valve is not resealing. That is the diaphragm or bypass issue covered in why a Sloan flushometer keeps running.
EPA names the first problem directly: "If not properly programmed, operated, and maintained, automatic flush sensors can cause unnecessary double or “phantom” flushing, which increases the water used at a facility."
Could the extra flush be normal?
Sometimes, yes. Check the model's features before you chase a fault. Zurn's retrofit sensor sheet describes a "courtesy flush within two seconds after a person is first detected," then says "the main flush will occur when the user steps away from the fixture." That looks like two flushes, and it is one design.
The same sheet lists an automatic flush "24 hours after the last flush" that can be switched on or off. Zurn's connected model lists a "48 or 168 hour trap seal flush." A toilet that flushes once in an empty restroom at a steady interval is probably doing exactly that. The settings are owner-selectable, so a facility manager can turn them on or off.
What makes a sensor flush with no one there?
Zurn's troubleshooting table for its ZEMS-W1 valve lists the causes of a valve that "ghost flushes or activates randomly with no user present":
- A dirty sensor lens. The corrective action is "Clean lens."
- Power supply output out of tolerance. "DC voltage must be between 6-9 VDC." Check for a power fault or replace the supply with the maker's converter.
- A sensor viewing the stall door. Re-calibrate the sensor.
The calibration section is blunt about the last one: after setting the range, stand outside the closed stall and check that the sensor does not see the door, and "FAILURE TO DO SO WILL RESULT IN “GHOST” FLUSHING." Zurn also says calibrating to a distance of less than 18 inches from the sensor face may result in false activation.
The older battery retrofit sensor gives similar clues in its light codes. Its table says the red light flashes when no user is present if there is an "Obstruction in front of the sensor," the "Sensor range set too long," or the "Sensor is detecting opposite wall." A new partition, a mirror, a door that swings open or a freshly polished panel can change what the sensor sees.
What if the valve flushes repeatedly when power comes on?
Look at the power supply. Zurn's table lists "Repeated valve activation when power is provided" with the cause "Insufficient DC power level (less then 6 VDC)," and the fix is to upgrade to the newer Zurn power supply. Low voltage can also be a failing battery pack on a battery model, which Zurn flags with a flashing red light. Electrical work on a hardwired valve belongs to a qualified person, not a quick fix with a wire.
What can you do safely before calling someone?
- 1Clean the lens with mild soap and water. Zurn tells owners not to use abrasive or chemical cleaners on the valve and to protect sensor lenses from cleaning chemicals.
- 2Look for new objects in front of the sensor, including a door that now swings open toward it.
- 3Close the control stop if the toilet is wasting water. This is the shut-off screw where the supply pipe meets the valve, and it isolates one fixture without taking the restroom out of service.
- 4Note the model and the light pattern so the next person can match it to the right manual.
Recalibrating or replacing a power supply is a job for someone with the model's instructions. EPA's guidance for facilities also says that if automatic sensors are installed, "check and adjust them to ensure proper settings and operation and avoid double or phantom flushing," and to post signage and train users to report continuously flushing toilets.
For a map of every way these sensors fail, see how auto-flush sensors fail on commercial toilets and urinals.
For the opposite problem, a sensor that never fires, see why a sensor-operated commercial toilet will not flush. To understand the parts you are looking at, read how a flushometer valve works. HQ is licensed and insured and offers 24/7 service if a restroom needs to be back in use fast.