Commercial Toilet Keeps Running: How to Diagnose and Fix a Flushometer
If a manual commercial flushometer will not shut off, close the control stop first. Common causes include a blocked metering bypass, debris under the diaphragm, damaged internal parts, the wrong repair kit, or inadequate supply pressure.
Match the symptom before you touch anything
Good maintenance starts by describing what the system is actually doing. Use the pattern below to decide where to look first.
| What you see | What it points toward | First move |
|---|---|---|
| Continuous full flow | Blocked bypass, debris, damaged relief assembly | Shut off water; inspect and clean internals. |
| Flush lasts too long | Restricted bypass or wrong-volume parts | Verify kit and metering path. |
| Weak flush | Stop too closed, wrong kit, poor supply | Adjust stop gradually; compare nearby fixtures. |
| Handle leaks/sticks | Worn handle assembly | Use correct handle repair kit. |
Tools and preparation
What to bring
- Flat-blade screwdriver
- Smooth-jaw adjustable wrench
- Rags or towel
- Correct diaphragm/inside-parts kit
Before you start
- Confirm the exact location and complaint.
- Photograph labels, settings, and error codes before changing anything.
- Know how to isolate water, power, or the affected area if needed.
- Follow site-specific PPE, lockout/tagout, ladder, roof, and access procedures.
Step-by-step
Identify the valve
Record manufacturer, series, toilet/urinal type, and flush volume before ordering parts.
Close the control stop
Turn clockwise gently; do not force a seized stop.
Relieve pressure and open the top
Operate the handle once, catch residual water, and remove the top cover carefully.
Inspect the diaphragm assembly
Look for grit, scale, torn rubber, distorted plastic, and debris on sealing surfaces.
Clean the metering path
Rinse serviceable parts. Never enlarge the small bypass opening.
Install the correct kit
Match manufacturer, fixture type, and flush volume; seat parts naturally.
Restore water and test
Open the stop slowly, check for leaks, and test several flushes.
Common mistakes
- Buying a kit because it looks similar
- Using toothed pliers on chrome
- Forcing a stuck control stop
- Poking the bypass with wire or a drill bit
- Opening the control stop fully by default
When to stop and hand it off
- Control stop will not shut off or is leaking
- Valve body or supply piping is cracked/corroded
- You cannot positively identify the correct parts
- Several fixtures suddenly have pressure problems
- Correct internal service does not stop the run-on
Frequently asked questions
Why does a clogged bypass make it run?
The bypass meters water into the upper pressure chamber so the diaphragm can close on time.
Are toilet and urinal kits interchangeable?
Do not assume so; flush volumes and metering parts can differ.
Should the control stop be fully open?
No. Open only enough for reliable fixture performance.
Can I use a paper clip to clear the bypass?
No. Use the manufacturer-approved cleaning method without enlarging the opening.
Related BuildingWrench guides
BuildingWrench provides general educational information for commercial-facility maintenance. Manufacturer instructions, applicable codes, site procedures, and required trade qualifications always take priority.