A no-tank flushometer that runs nonstop usually has a worn diaphragm, stuck solenoid, or misadjusted stop—shut water off and service the valve.
Endless flushing wastes water, raises bills, and can damage finishes. Good news: most no-tank toilets use a standard flushometer. That makes diagnosis methodical. This guide shows quick checks, the parts to service, and when to call a pro. You’ll find a broad cause-and-effect table early and a parts/time table later for planning.
Tankless Toilet Keeps Running: Fast Checks
Run through these simple checks before grabbing parts. They solve a large share of nonstop-flush problems.
- Close the control stop. Use a flat screwdriver on the stop to throttle or shut off supply. This halts the water while you work.
- Pop the top cap. Remove the flushometer cover to reach the diaphragm/inside parts (manual) or the solenoid and sensor module (sensor models).
- Match parts to the fixture rating. The diaphragm or relief valve must match the flush volume stamped on the bowl. A mismatch can cause long or run-on flushes.
- Check for debris. Sediment can clog the tiny bypass orifice in the diaphragm. A clogged bypass prevents the upper chamber from filling, so the valve never closes.
- For sensor units: install fresh batteries, confirm the target distance, and listen for a clicking solenoid. A solenoid stuck open will pour water continuously.
Common Causes And Quick Tells
| Cause | What You See | DIY Or Pro? |
|---|---|---|
| Worn diaphragm or relief valve (manual) | Long flush that never tapers off; handle feels normal | DIY: Replace inside kit |
| Clogged diaphragm bypass or filter screen | Valve won’t “seat”; nonstop flow after flush | DIY: Clean or replace diaphragm |
| Control stop opened too far | Overpowering flow; splash; extended run-on | DIY: Back off ¼ turn at a time |
| Solenoid stuck open (sensor) | Constant flow; sensor light normal or dim | DIY or Pro: Replace solenoid |
| Low batteries / sensor interference | Random flushes; won’t time-out; frequent cycling | DIY: New batteries; clear sensor path |
| Vacuum breaker failure | Leak at spud/vacuum breaker; dribble post-flush | DIY: Replace vacuum breaker |
| Supply pressure spikes | Chatter or surging; extended closing time | Pro if severe; add PRV as needed |
How A Flushometer Closes The Flow
Inside the valve, a flexible diaphragm splits an upper chamber from the main water path. During a flush, a relief event vents the upper chamber, the diaphragm lifts, and water rushes to the bowl. The valve closes only after the small bypass refills the upper chamber. If that bypass is clogged or if the diaphragm can’t seal, water never stops. For diagrams and part names, see Sloan’s Regal troubleshooting and diaphragm service guides.
Step-By-Step Fixes For Constant Flushing
Manual Flushometer (Handle-Operated)
1) Isolate Water And Remove The Cover
Turn the control stop clockwise to stop the flow. Hold the cover firmly, then unscrew and lift. Keep a towel handy.
2) Inspect And Clean The Diaphragm
Lift out the diaphragm/inside parts. Rinse under clean water. Look for tears, mineral buildup, and a blocked bypass. A toothpick can clear the tiny orifice; don’t enlarge it. If the rubber looks stiff, swap in a matched kit rated for the bowl’s flush volume.
3) Check The Relief Valve And Inside Cover
A nicked relief valve or cracked inside cover can keep the valve from seating. Replace worn pieces using the matching inside-parts kit. This swap takes minutes once the water is off.
4) Reset The Control Stop
Open the stop slowly. Aim for a strong, brief flush that tapers and stops. If it runs on, back the stop down in small increments until the closing action is smooth.
Sensor-Activated Flushometer
1) Fresh Batteries And Sensor Basics
Install new batteries and reset the module. Confirm the target distance and make sure nothing blocks the sensor’s “view.” Wall items or shelves can confuse some designs. Kohler’s WAVE notes that obstructions above the sensor can cause erratic operation, so keep that sightline clear; see Kohler’s WAVE touchless troubleshooting.
2) Listen For The Solenoid
Trigger the sensor. A healthy solenoid makes a crisp click. Buzzing with no change, no click at all, or constant flow points to a stuck or failed solenoid. Replace the solenoid per the model’s procedure. Many units place it under the cover with a simple clip and gasket.
3) Clean The Diaphragm On Sensor Models
Sensor versions still rely on a diaphragm to close. Remove the cover, pull the module, and service the diaphragm as you would a manual valve. A clogged bypass is a classic cause of nonstop flow on these units.
Vacuum Breaker, Spud, And Leaks That Mimic Running
Water leaking at the vacuum breaker or spud can look like a run-on flush. Replace the vacuum breaker kit if you see drips after the cycle. Tighten couplings evenly so the outlet lines up without stress.
Match Parts To The Fixture Rating
Flush volume ratings are stamped on the bowl (closet or urinal) and sometimes on the valve body. Use a diaphragm and relief valve with the same rating. A low-consumption diaphragm on an older bowl can hold the valve open too long. A water-saver kit on a high-efficiency bowl can starve the siphon. The right kit cures both problems and brings the cycle back within spec. Sloan’s service material above shows part families and how they interact with bowl ratings.
Water Quality, Debris, And Pressure Tips
Hard water and construction debris clog bypasses and screens. If your building recently saw a shut-off or repair, expect sediment. Clean the diaphragm and the stop’s strainer. If pressure surges are common, a pressure-reducing valve on the branch can calm the close. Chatter during closing is a tell for pressure swings and damaged rubber parts.
What To Do If The Valve Still Runs
At this point you’ve cleaned, matched, and adjusted. If the valve still won’t close cleanly, install a complete inside-parts kit for your model. That refresh swaps all wear items in one move. If a sensor unit keeps flowing with a brand-new solenoid and diaphragm, the body may have pitting at the seat. That requires a pro assessment or a body replacement.
Parts, Time, And Planning
| Part/Task | Typical Range | Time |
|---|---|---|
| Inside-parts kit (manual) | Low to mid cost; model-specific | 20–40 minutes |
| Solenoid assembly (sensor) | Mid cost; battery type varies | 15–30 minutes |
| Vacuum breaker kit | Low cost | 10–20 minutes |
| Complete valve rebuild | Mid cost kit | 45–60 minutes |
| Body replacement | Higher cost part | 1–2 hours (pro) |
Tools You’ll Want Nearby
- Flat screwdriver for the control stop
- Adjustable wrench for couplings
- Clean rag or towel; small bucket
- Toothpick or nylon bristle for the bypass orifice
- Model-matched kit (diaphragm, relief valve, gaskets)
- Fresh batteries for sensor units
When To Call A Plumber
Call a pro if any of these pop up:
- Corroded or pitted valve seat inside the body
- Stripped cover threads or seized couplings
- Recurring debris from upstream piping
- Heavy pressure swings across multiple fixtures
Prevention Checklist For No-Tank Toilets
- Set a quick service rhythm. Clean the diaphragm and screen during routine janitorial cycles in high-use restrooms.
- Keep spares on hand. One inside-parts kit and one vacuum breaker kit per restroom keeps downtime short.
- Protect the sensor sightline. Avoid shelves or bars above the eye of the sensor; some brands warn that overhead obstructions cause misreads (see Kohler’s WAVE page linked earlier).
- Replace batteries on a schedule. Don’t wait for intermittent misreads or random flushes.
- Open the stop just enough. Too much flow can lengthen the cycle and splash.
Fast Reference: Symptom To Fix
- Runs nonstop after a handle push: clean or replace the diaphragm; verify relief valve; back off the stop.
- Runs without anyone nearby (sensor): new batteries; clear the sightline; replace the solenoid if stuck open.
- Leaks at the spud or vacuum breaker: replace the vacuum breaker kit and align the outlet.
- Chatter during closing: inspect pressure, refresh diaphragm, and set the stop.
Why These Fixes Work
The flushometer closes only when the upper chamber refills through a tiny passage. Dirt blocks that passage. Worn rubber can’t seal. A stuck solenoid keeps the relief path open. Clean passages and fresh parts restore the pressure balance so the diaphragm can drop and seal. For deeper diagrams and part names, the Sloan Regal troubleshooting PDF and Sloan’s diaphragm service deck show the flow path and service order, and Kohler’s WAVE touchless notes flag sensor-area pitfalls.
Wrap-Up Fix Plan
- Shut the control stop and remove the cover.
- Clean the diaphragm and bypass; swap in a matched inside-parts kit if wear shows.
- Set the stop for a strong, brief cycle.
- For sensor models, add batteries, confirm aim, and replace a sticky solenoid.
- Replace the vacuum breaker if you see drips at the spud.
- Call a pro if the body seat is damaged or pressure swings are severe.
Follow that order and the endless flush should end fast. The fixes are straightforward, the parts are common, and the results are immediate.