Auto-flush sensors on commercial toilets and urinals fail in a handful of ways: dead batteries or a weak power supply, a dirty or covered sensor window, a range set wrong for the stall, a failed solenoid, or a damaged cable. Each shows a different symptom, such as no flush, a blinking light, or random flushing.
Which failures are power failures?
Batteries and power supplies. Zurn's battery retrofit sensor lists battery life of "3 years at 4,000 flushes per month," and its troubleshooting table gives "Expired batteries" as a cause of a valve that will not operate. The sensor also warns you: "the red light will flash when an object is detected" once the batteries reach the caution level.
Hardwired valves fail differently. Zurn's connected-valve table says the DC voltage "must be between 6-9 VDC," and lists "Repeated valve activation when power is provided" with the cause "Insufficient DC power level (less then 6 VDC)." So low power can cause either no flush or too many.
Which failures are the sensor window and range?
The sensor works by reflected light. Zurn describes "invisible light rays" that are "reflected back to the sensor's receiver" when a user comes into range. A dirty lens or a reflective surface confuses it. Zurn's table lists "Sensor lens is dirty" as a cause of both a valve that will not operate and one that "ghost flushes or activates randomly with no user present."
Range matters too. The retrofit sensor's table shows the red light flashing with no user present when there is an "Obstruction in front of the sensor," the "Sensor range set too long," or the "Sensor is detecting opposite wall." Set too short, the valve will not see a user at all. See why a commercial toilet keeps flushing and why a sensor toilet will not flush.
Which failures are the solenoid?
The solenoid is the small electric valve that the sensor signals. Zurn's retrofit table gives "Solenoid problem" as a cause of three symptoms: a valve that will not operate, a valve that "does not shut off," and not enough water to the fixture. Its fix in each case is to replace the solenoid. A solenoid that sticks open looks like a running valve, which is why a Sloan-style run-on can have an electrical cause as well as a diaphragm one.
Which failures are not the sensor at all?
The water side. Zurn's tables list a closed control stop, low supply pressure, a plugged bypass and a worn diaphragm in the same guides. A sensor can fire correctly and the valve still deliver a weak or endless flush. For urinals, why a urinal is not flushing sorts the supply and kit causes from the sensor ones.
How do you prevent most sensor failures?
EPA's guidance for urinals is to "annually check and adjust automatic sensors, if installed, to ensure they are operating properly and avoid double or “phantom” flushing." Keep chemical cleaners off the lens: Zurn says to protect sensor lenses from cleaning chemicals and to clean chrome with mild soap and water. Replace batteries on a schedule, and write the valve model on the restroom log so the right manual is at hand.
Hardwired power repairs and valve internals call for someone with the model's instructions. HQ is licensed and insured and gives free estimates on commercial restroom plumbing.