A flushing urinal should flush once after each use, and the 2024 IPC requires the trap seal to refill after every cycle. Sensor models can also run a timed flush when idle, such as Zurn's 24-hour automatic flush or 48 or 168 hour trap seal flush. No code sets a number of flushes per day.
How often should a urinal flush when people use it?
Once, after each user. The 2024 IPC requires every flushing fixture to have a flushing device "designed and installed to supply water in quantity and rate of flow to flush the contents of the fixture, cleanse the fixture and refill the fixture trap." For a flushometer valve it adds that "the trap seal to the fixture shall be automatically refilled after each flushing cycle."
That refill matters as much as the rinse. The water left in the trap is the seal that keeps sewer gas out of the room. A urinal that does not flush after use is not only dirty, it is not reliably resealing the trap. If one will not flush at all, see why a urinal is not flushing.
Phoenix amended Table 604.4(1) so a urinal is capped at 0.5 gallon per flushing cycle (buildings that meet the listed exceptions use Table 604.4(2) instead). Phoenix's amendment list does not include Section 415, so the flushing-device rules above apply as the model code states them.
How often should an idle urinal flush?
The code does not give a number. The manufacturer's setting does. Zurn's retrofit sensor can run an "automatic flush 24 hours after the last flush," and the option can be turned on or off. Zurn's connected sensor valve lists a "48 or 168 hour trap seal flush." Those are product settings, not code requirements, and the maker's sheet for your model is the one to follow.
A timed idle flush earns its water in a restroom that sits unused, such as a weekend-closed office or a seasonal facility. In a busy restroom it rarely triggers, since the timer counts from the last flush.
Why do sensor urinals sometimes flush twice, or flush less?
Two features change the pattern. Zurn's sensor offers a courtesy flush, which flushes "when an object has been detected for two seconds" and then returns to normal mode. It also offers a Urinal Water Saver aimed at "a stadium or civic arena, where a continuous line of users wait to use a urinal." During continuous use it flushes "a partial volume of water after two consecutive users have been sensed and a new user enters the range of the sensor within five seconds of the previous user leaving."
Both are switch-selectable on that model. Another site's urinal may behave differently, so look up the model before deciding that a pattern is a defect. If a urinal flushes with no one there, the page on commercial toilets that keep flushing explains lens, range and power causes that apply to urinal sensors too.
What about trough urinals and timers?
EPA notes that "New trough urinals either use flushometer valves on preset timers (e.g., hourly, for halftime at a football game) or are equipped with electronic sensors that detect a user at the trough." The hourly example is EPA's illustration, not a rule. The IPC also lets a flush tank used for automatic flushing be controlled "with a timing device or sensor control devices."
Does a waterless urinal flush at all?
No. It has no flush valve. Its upkeep is a cartridge or sealant routine and a periodic drain flush, which varies by maker. Kohler's waterless urinal guide, for example, calls for a flush-out cleaning "every two weeks." See waterless vs flush urinals and whether waterless urinals are allowed in Arizona.
How do you know the flush itself is right?
Time it. EPA says "At least annually, inspect diaphragm or piston valves, and replace any worn parts," and gives an estimate: a properly functioning 1.0 gpf urinal valve "should not have a flush cycle longer than four seconds." Its equation multiplies seconds by 0.25 for a urinal. A valve that runs long wastes water, and one that runs short may not clear the bowl.
EPA also says to "annually check and adjust automatic sensors, if installed, to ensure they are operating properly and avoid double or “phantom” flushing." Put that on the calendar in a commercial plumbing preventive maintenance plan. HQ gives free estimates on commercial restroom plumbing.