Why does my Sloan flushometer keep running?

A flushometer flushes by borrowing the pressure already in the supply line. At rest, water sits on both sides of the diaphragm, and the higher area on top holds the valve shut against the seat. Press the handle and a small relief valve opens, releasing the water above the diaphragm. The pressure difference lifts the diaphragm and sends a measured slug of water to the fixture. As that upper chamber refills through a tiny bypass orifice, the diaphragm settles back onto the seat and the flush ends. The whole cycle takes a few seconds.

When the valve runs continuously, that refill step has failed. The most common reason is a clogged bypass orifice. That orifice is a pinhole, and it fouls easily. Grit, pipe scale, and bits of debris from the line can plug it. In buildings with over-treated or softened water, a soft gelatinous film can form and coat the orifice and the diaphragm. With the bypass blocked, the upper chamber never refills, so the diaphragm never reseats and water keeps flowing.

The second cause is a relief valve that does not seat. If the small rubber relief valve at the center of the assembly is swollen, nicked, or held off its seat by debris, it bleeds the upper chamber faster than the bypass can refill it. The third cause is a worn or damaged diaphragm: years of cycling stretch and harden the rubber, and a torn or enlarged diaphragm cannot hold the seal. Hard water speeds all of this up, which matters in Phoenix.

Work the problem in order. Most running flushometers are fixed by cleaning, not replacing, but you need the valve apart to know which part failed.

1. 1Close the control stop. The control stop is the small screw fitting on the side of the valve where the supply pipe enters. Turn it clockwise with a flat screwdriver or a fitting wrench until the water stops. This isolates the one valve so the restroom can stay in service.
2. 2Remove the outer cover and inner cover. Unscrew the chrome outer cap by hand or with a smooth-jaw wrench, then lift out the inner cover that holds the diaphragm assembly. Catch the parts; they are small.
3. 3Lift out the diaphragm assembly. Note how it sits so you can return it the same way. Keep the parts in order on a clean cloth.
4. 4Clean every part under running water. Rinse the diaphragm, the relief valve, and the bypass orifice. Do not ream the orifice with a pin or wire, which can enlarge it and ruin the flush volume. Wipe away any film or scale and flush grit from the seat in the valve body.
5. 5Inspect the diaphragm and relief valve. Hold the diaphragm to the light. If it is stiff, cracked, swollen, or the relief valve looks chewed, replace the assembly with a rebuild kit.
6. 6Reassemble, open the control stop slowly, and test. Reinstall in reverse order, hand-tighten the covers, then reopen the stop a partial turn and watch a flush. The valve should cut off cleanly. Adjust the stop so the flush delivers a strong, full cycle without splashing.

If cleaning alone fixes it, you are done. If the valve still runs, the diaphragm is worn and needs the rebuild kit.

This is the step people miss. A flushometer is engineered to deliver a specific volume, and the diaphragm assembly meters that volume. Install the wrong kit and the fixture will either under-flush and clog or over-flush and waste water. The diaphragm assembly is what sets the gallons per flush (gpf), so it has to match the fixture and the original valve rating.

Federal law caps the volume, and WaterSense sets a tighter target. Standard toilets are limited to 1.6 gpf, while WaterSense-labeled toilets use 1.28 gpf or less. Urinals run lower still: the federal flush-urinal maximum is 1.0 gpf, and WaterSense urinals use 0.5 gpf or less. EPA notes that, for flushing urinals and flushometer-valve fixtures, "the flush volume is determined by the flush valve, not the fixture," which is exactly why the rebuild kit you choose controls how much water the toilet or urinal uses.

Sloan codes its diaphragm kits to the volume. The Royal line is a good example: the A-1101-A diaphragm kit is the 1.6 gpf water-closet rebuild kit. There are matching kits for 1.28, 1.0, and 0.5 gpf fixtures. Read the rating stamped on the valve cover or the original diaphragm and buy the matching kit. Zurn and other flush-valve makers code their diaphragm kits the same way, so the rule holds whatever brand is on the wall: match the gpf, do not guess.

Sloan builds flushometers in two families, and which one you have changes the repair part. Diaphragm valves use the flexible rubber diaphragm described above and are the most common in modern commercial restrooms. When a diaphragm valve runs, you clean or replace the diaphragm assembly and its bypass.

Piston valves use a molded cup or piston that slides in the valve body instead of a flat diaphragm, with a clutch and a similar bypass passage. The failure modes look the same from the outside, a valve that will not stop running, but the internal part is a piston rebuild kit rather than a diaphragm kit. Before you order parts, open the valve and confirm which mechanism is inside, or read the model number on the valve body. The Sloan Royal and Regal lines, for instance, are diaphragm valves, and the parts pages list the correct kit by model.

One more field note: a flushometer needs enough line pressure to work. The plumbing code's Table 604.3 sets the minimum flow pressure for a flushometer valve at 15 psi, far above the roughly 8 psi a tank toilet needs. If a valve flushes weakly or hunts, low supply pressure or a half-closed control stop can be the real problem, not the diaphragm.

Two local conditions wear flushometers faster here. First, Phoenix water is hard. City reports put total hardness around 10 to 17 grains per gallon, which the U.S. Geological Survey classifies as hard to very hard. Scale builds on the seat and in the bypass and shortens diaphragm life. Second, water that is over-treated or over-softened leaves the gelatinous film that plugs the bypass orifice in the first place. Buildings that run aggressive softening on the whole supply often see more running flushometers, not fewer.

A short maintenance habit prevents most callbacks. Put flushometer checks on a routine commercial preventive-maintenance walk, cycle each valve, and watch for a clean cut-off. Rebuild diaphragms on a schedule in hard-water buildings rather than waiting for failures, and keep the rebuild kits that match each fixture's gpf on the shelf so a running valve is a five-minute fix. Replace, do not ream, a worn bypass, and clean parts under running water so you do not push grit back into the seat.

Call a commercial plumber when a valve keeps running after a full rebuild, when several valves fail at once (a sign of a water-quality or pressure problem upstream), or when the control stop or supply itself is leaking. HQ Plumbing & Air services commercial restrooms across metro Phoenix and can rebuild or replace flushometers and diagnose the water-quality issues behind repeat failures. For tank-type fixtures, see our guide on how to fix a running toilet, and for urinal choices see waterless versus flush urinals.