Adjust a flushometer at the control stop, using the screw in the center of the stop cap. Open it a little at a time while flushing until the fixture clears without splashing and runs quietly. The stop sets flow rate. The valve kit sets gallons per flush.
Where is the adjustment on a flushometer?
On the control stop, the fitting where the supply pipe meets the valve. Zurn's Aquaflush sheet says the stop "can be opened and closed by using the adjusting screw located at the center of the stop valve cap, behind the stop snap cap screw cover if already installed." It adds that "it is not necessary to remove the stop valve cap when making adjustments."
The code expects this control to exist. The 2024 IPC says "Each flushometer valve shall be provided with a means for regulating the flow through the valve." Many valves also have a vandal-resistant cap over the stop, so you may need the maker's key or tool to reach the screw.
What does the control stop actually change?
Flow rate into the fixture, not the gallons the valve is built to deliver. Zurn says its Aquaflush valves "are preset for fixture volume as marked on the valve cartons" and that the valve "does not require regulation for variation in water pressure within its operating range." The preset volume comes from the diaphragm or piston kit. Chasing a weak flush with the stop will not fix a worn kit.
EPA gives a related instruction to facility managers: "Periodically check to ensure the control stop ... is set to fully open during normal operation." It separately says to adjust the flush volume "following the manufacturer's instructions" and to "periodically inspect the flush volume adjustment screw to ensure the flush volume setting has not been modified from the original settings." Valve designs differ, so read the sheet for your model. When the sheet and a rule of thumb disagree, the sheet wins.
How do you set the control stop step by step?
- 1Confirm the pipes were flushed. Zurn says to flush the supply lines of debris before connecting, and to repeat that after any seasonal drain-down.
- 2Start with the stop nearly closed. Zurn's instruction is to "gradually adjust the stop valve open, using the adjusting screw, while actuating the valve."
- 3Flush and watch the bowl. Keep opening the stop a bit at a time until "the rate of water flow into the fixture is not excessive, yet is sufficient enough to adequately evacuate the waste."
- 4Check for splash and noise. Zurn's sensor valve sheet says proper adjustment is made when "the plumbing fixture is cleansed after each flush without splashing water out from the lip" and "a quiet flushing cycle is achieved."
- 5Test urinals back to back. For urinals, Zurn says the final setting should be one where "the fixture will not overflow when the valve is actuated in succession."
- 6Close it up. Replace the stop cap screw cover after the final setting.
Do not open the stop wider than the bowl can handle. Zurn's FV666 manual says "Control stop should never be opened to allow flow greater than fixture is capable of evacuating. In the event of valve failure, fixture must be able to handle a continuous flow." A fixture that cannot drain a full-open valve will overflow the day the valve sticks.
What do you do if the flush is wrong and the stop does not fix it?
Match the symptom to the cause. Zurn's tables give these pairs:
- Water splashes out of the fixture: supply volume is more than necessary, so adjust the stop down, or lime has built up on the bowl's rim holes.
- Not enough water to flush: the stop is not open enough, the supply volume or pressure is low, or the wrong kit is installed, such as a urinal kit in a closet valve.
- Flush is loud: the stop is not set for quiet operation, or the bowl or the piping is making the noise. Zurn notes that piping noise can come from a missing air chamber or shock arrestor, loose pipes or the wrong pipe size.
A weak flush that survives adjustment belongs in why a commercial flushometer toilet does not flush fully. A valve that will not shut off belongs in why a Sloan flushometer keeps running.
How do you adjust a sensor flushometer?
Sensor valves add a range setting. On Zurn's retrofit sensor, the detection distance is "field adjustable from 12 to 60 inches," with the range screw turned clockwise to increase it and counterclockwise to decrease it. On the connected model, Zurn warns that calibrating the sensor to a distance of less than 18 inches from the sensor face may result in false activation. Range mistakes cause repeat flushes, which the page on commercial toilets that keep flushing covers.
For how the whole valve fits together, see how a flushometer valve works. A licensed plumber is the right call when the stop is seized, the valve body leaks, or the supply is below the pressure the fixture needs. HQ gives free estimates and upfront pricing.