A touchless faucet that will not run is usually short of water, power or detection. Check the supply stops, batteries and cable, then the sensor lens for dirt or leftover protective film, then whether it clicks when you wave a hand. A click with no water points to a clogged solenoid screen; no click points to power or the solenoid.
What should you check first?
The basics, in this order. Delta's troubleshooting guide for its 591T touchless faucet says if the unit does not operate: check that the lens "is not blocked with foreign matter," that the "vinyl scratch protector" is removed from the sensor if present, that the "power cable is properly secured in fitting," that the "batteries are fresh and properly installed," that the "two wires to solenoid" are connected correctly, and that the "water supply is turned on."
Zurn's older battery-faucet guide lists the same starting points under "Faucet will not flow water": "Water supply not turned on," "Batteries not connected," a cable connection that is not fully engaged, and a low battery. Its newer manual adds a line for a new install: "Check if protective film was removed from lens."
How do you check the supply?
Look under the sink. Both Zurn and Delta put the water supply at the top of the list, and it is the quickest to rule out. Make sure the supply stops are open. Zurn's table says to "Check supply stops. Turn on water." If there is a mixing valve upstream, Delta's guide says to check "for a pressure lock between the mixing valve and the solenoid" by shutting the supply off and undoing the connection at the solenoid inlet to relieve built-up pressure.
What does a battery or power problem look like?
On Zurn's battery faucet, a flashing red light in the sensor eye means low battery, and the remedy is four new alkaline batteries. Delta's battery faucet gives audio signals: it "beeps twice when turning off" to indicate the batteries are low, with "1500 cycles or 2 weeks left," and it "beeps continuously when hands in front of spout and no water" when it is "locked out because batteries are too low." On a hardwired Delta faucet, the guide says to check the voltage from the converter and transformer, around 6.4 volts DC to the driver board.
Do not assume the batteries are fine because they are new. Check the cable connection too. Zurn says to look for "broken pins" on the connector, and its newer manual says missing, bent or broken pins mean the electronic box needs to be replaced.
What does the solenoid click tell you?
The solenoid is the small electric valve that actually opens the water. Both makers use the click as the dividing line. Delta says the solenoid should click when the sensor activates it, and that a click "indicates that both the sensor and the solenoid are functioning." Zurn says to "move hand in front of faucet to see if solenoid valve is clicking."
- A click and no water: the sensor is working. Zurn says to open the solenoid and clean it. Delta says to make sure the "inlet screen on solenoid is not plugged with debris" and to check the incoming supply pressure and volume.
- No click: the sensor or power is the problem, or the solenoid has failed. Delta's steps are to look for a pressure lock, and if there is still no click, to replace the solenoid.
- Zurn's filter: its guide also lists a plugged filter, with the fix to shut off the water, remove the clean-out cap and clean it.
Is the sensor not seeing hands?
Several things confuse a sensor. Zurn's newer manual lists a lens with "surface damage, scratches, or deposit build ups," and a lens "obstructed by environmental factors such as highly reflective surfaces or bright lighting conditions," adding that "direct sunlight could effect unit operation." It describes sensitivity settings you can change on the faucet's switches and a calibration routine that sets the activation distance. Delta's faucet lets the owner choose a sensor range from 3 to 15 inches, with a default of 9 inches, and notes the range varies by about an inch with environmental conditions.
One more cause looks like a failure. Delta's guide says "when the faucet detects an object for longer than 45 seconds, it will automatically shut off until the object is removed." Zurn's battery faucet does the same after 30 seconds. A bucket, a sponge or a cleaning cloth left in the basin can shut the faucet down. Remove it, and the faucet "will operate normally" again.
When is it time to call a plumber?
If the supply is open, the batteries are good, the lens is clean and clear and the solenoid does not respond, the next steps are a solenoid or electronics replacement, and those work best with the model's manual in hand. Delta's guide ends with a call to its technical service line, and Zurn's says to contact its support. A faucet that leaks under the sink or will not shut off is also a plumber's call, since the problem may be a failed gasket or a damaged connector, as Zurn's table notes.
Worth knowing: a faucet that stops after a set time is not broken. Zurn's newer manual lists 30 seconds as the standard run time. If water pressure is the issue across the restroom, see low water pressure at one fixture, and for a push-type public faucet that will not shut off, push-button metering faucet won't shut off covers it. If it runs but the stream is weak, low water flow from one faucet covers aerators. HQ is licensed and insured and gives free estimates on commercial plumbing.