An HMI panel has no internal tag that triggers a restart: the documented paths are the reboot command in the panel's settings screen or programming software, and cycling power to the panel alone. Confirm the machine keeps running with the panel dark, pick the software path when you can, and treat a freeze that returns as a fault to diagnose.
When a panel screen freezes mid-shift, the first question on the floor is whether a tag can restart it without touching power. On the panels where this question keeps coming up, the documentation names no internal tag for the job. Two restart paths are supported: the reboot command reached through the panel's settings screen or its programming software, and cycling power to the panel alone. The order matters more than the choice. A panel restart is routine only when the machine keeps running with its operator screen dark. That is a property of your wiring and your process, confirmed once on purpose before an emergency forces the question. Work through it in this order: read the machine first, check the power path, use the software reboot when you can, verify the recovery, and treat a freeze that comes back as a fault with a cause.
Is there an internal tag that reboots an HMI panel?
No: on the panels where this question comes up, the maker's documentation names no internal tag that triggers a restart. The two supported paths are the reboot command in the panel's own settings screen and cycling power to the panel alone.
That answer is worth checking against your own panel before you rely on it, because families differ. Open the manual for the exact model and search the index for 'reboot'. Current documentation for one widely installed panel family states there are two ways to reboot, recommends the software route, and gates it behind an administrator-class login. Where the command lives also varies: look in the panel's settings application, which many panels reach from a setup or control-panel screen, and in the programming software's transfer or diagnostics menu on your PC. If your manual and your HMI software's function list name no restart command, take the answer at face value. A button you add to the application has nothing documented to call, so the two supported paths are the only paths.
How do you tell a frozen panel from a stopped machine?
Read the machine, then the screen: a frozen display is a display problem only when the controller's status LEDs and the machine's own indications show the process still running, and that check takes under a minute.
A frozen screen by itself tells you nothing about the controller, so read the indications you already have before you touch anything. The symptoms sort like this:
- Screen frozen, touch dead, controller RUN LED green, product still cycling. A display-side fault. The restart paths apply, and the machine needs nothing from you first.
- Screen responsive but values stale or stuck at old numbers. A communications fault. A reboot will not repair a broken cable or a failed switch; find the break in the path first.
- Screen dark and the machine stopped. A power fault. Rebooting is not the job; restore power and find what dropped it.
- Application error at startup, or a panel that boots to an error screen. A project or storage fault. Restarting changes nothing; go to your backup.
- Panel and controller both dark. Machine power. Nothing here applies; work the machine's own procedure.
If the indications disagree, or you cannot establish the machine state from where you stand, treat it as a machine problem: use the approved stop procedure and sort the panel out afterwards.
What must you confirm before you cycle panel power?
Confirm the machine keeps running with the panel dark before your first power cycle. The restart is only safe when the controller, its safety functions and the operator's view of status all survive the panel going offline.
Panel and controller are fed separately on a standard installation, so breaking the panel's supply leaves the controller and its outputs alone. Verify that on your drawing before you rely on it: trace the panel's disconnect and make sure it does not pass through the machine's main disconnect. Then run the confirmation the deliberate way, during a planned window. Take the panel offline while the line runs, watch the cycle count advance on the controller, and confirm the operators still have the status they need. The article on keeping PLC schedules running when the HMI panel is offline walks through what the controller side must survive.
One more check belongs before the first cycle, on a panel you have never restarted: know what it does with its project. Read what to check when an HMI panel loses its project after a power cycle, then cycle power knowing your panel's behavior.
If the panel is the operator's only view of a machine that stores energy or runs a safety function, treat its loss as a mode change and use the machine's approved stop procedure first; restarting the panel is never a way to clear an unsafe condition.
How do you reboot the panel from the programming software?
The programming software's reboot command restarts the panel without touching its power, and the panel's own settings screen offers the same restart where your panel documents one; on the documented panel family that route needs an administrator-class login, and the manual names four accounts that qualify.
For a frozen screen the settings screen is out of reach, so the software route is the one that works without touching power. Connect the PC that runs the programming software, go online with the panel, and use the reboot command your manual documents. Hold the administrator-class login before you need it: hunting credentials during a line-down restart turns a one-minute job into a support call. Write down any on-screen diagnostic text first, because it disappears at restart. After the restart, watch the boot complete, the application open, and one live value change against the controller before you close the laptop.
If the software refuses to connect, fix that first. The common culprits are the cable and the software version, and the article on wrong-version errors during HMI programming shows why the cable is the first suspect.
What does a safe reboot look like on a running line?
A safe reboot on a running line is a planned two-minute job: confirm the machine state, pick the software path when you hold an administrator login, keep the panel's power path as the fallback, and watch live values return before you walk away.
Example: filling line, screen frozen mid-shift
A filling line runs 8-second cycles. The HMI screen freezes for 12 minutes. The controller's RUN LED is green and filled bottles keep leaving the line, so the fault is display-side and the restart paths apply. The times below are illustrative planning numbers: assume a 2-minute walk to the panel's disconnect each way, a 15-second wait after the screen goes dark for the supply to discharge, and a 45-second boot to a live screen.
Two paths, two outcomes:
- Software reboot. The panel is on the plant network, the PC has the programming software and the administrator login, and the connection is live. Time: about 45 seconds of boot, with the machine running throughout. Production lost: none.
- Power cycle. No working software connection, so you walk. Time: 2 min walk + 15 s wait + 45 s boot + 2 min walk back = 5 minutes with no operator screen. Production continues, because the planned offline test proved the line runs with the panel dark, so the loss is visibility only.
The arithmetic: 2 min + 2 min = 4 min, and 15 s + 45 s = 60 s, so the power path takes 5 minutes and the software path 45 seconds. That is a saving of about 4 minutes 15 seconds and no opened power path.
Recommendation: Reboot from the programming software whenever the panel is reachable and you hold the administrator-class login; cycle power at the panel's own disconnect only when the connection is dead, and only on a machine you have already watched run with the panel dark.
Is a reboot the same as a factory reset?
No: a reboot reloads the application the panel already stores, while a reset to factory or maintenance mode erases the application and its settings, and the documentation for one panel family states the network address comes back as 0.0.0.0 until you set it again.
A frozen screen is a reboot problem, never a reset problem. The reset paths exist for a panel that will not start its application at all, and they are destructive by design: after one, you are restoring a project and re-entering settings, not watching a boot screen. That is why the backup comes before anything else. The safe backup-and-restore routine for an HMI panel project turns a lost application into a transfer job, because a panel you can restore is a panel you can recover from any restart mistake.
What if tag values must survive the restart?
Tags that live in the controller repopulate on their own once the panel reconnects, so only internal tags hold values you must protect, and one documented HMI software line gives those a per-tag persistence property it introduced at version 7.0.
Split your tags into the two classes and the problem shrinks. A tag bound to a controller address is part of the data exchange with the PLC: after every reconnect the panel reads it back from the controller, so a restart costs you nothing.
An internal tag is different. A counter the operators increment on the panel, or a setpoint typed into the screen, lives only in the panel and starts empty after a restart. That is what the persistence property is for. One HMI software package documents a per-tag 'Runtime Persistence' setting from its version 7.0 release onwards. Software older than that needs a script that saves the values and writes them back at startup. Check your own tag manual for the name it uses.
The sturdier design costs nothing extra: keep the master copy of any value the process depends on in the PLC, and let the panel display it.
When does a reboot not fix the problem?
A reboot restores a panel only for faults a restart clears, so the outcome of one controlled reboot sorts the remaining cases: values stay stale, the application fails to load, or the same freeze returns within the shift.
Each outcome has its own next step:
- The application loads but values stay stale. The comms path is the fault. Ping the panel's address, check the switch port and the cable ends, and read the controller's communications LEDs. Repeating the reboot cannot repair a device that has failed.
- The application fails to load, or the panel boots to an error. The project or storage is the fault. Restore from your backup, and if your panel accepts a project from a USB drive, the restore-without-programming-software route gets the screen back without the PC.
- The same freeze returns within the shift. The restart treated a symptom, and the fault has a cause. Log the time of each freeze, the panel model and software version, and the enclosure temperature. A pattern that clusters at the day's hottest hours points at heat in the enclosure, and the log is what the vendor's support will ask for. Repeated power cycling is not a repair, so book a diagnosis window and hand the vendor the record through its official support channel. If the machine also needs a notice or status screen that keeps working through faults like these, our shop-floor signage plays its content from a memory card or USB stick, offline.
Questions
Can I add a reboot button to my HMI application?
Only if your panel's documentation defines a restart function or system tag for it. Open the tag list and the system function reference in your HMI software and search for reboot or restart. If nothing is documented, a button you draw has nothing to call, and a guessed tag name is not a mechanism you can trust on a machine floor. Ask the panel vendor through its official support channel whether your exact model and software version offer a documented restart control, and what it does to stored values when it runs.
How long should panel power stay off during a power-cycle reboot?
The panel documentation publishes no minimum off time for a restart by power cycling. The practical target is a fully discharged supply: wait until the panel's indicator lights have gone dark, give it a few seconds more, then reapply power at the panel's own disconnect. Where you break the circuit matters more than how long: the panel's disconnect only, never the machine's main disconnect, which takes the controller down with it.
What should I record before restarting a frozen panel?
Note the time, write down the exact text on the screen, and photograph the display before you touch anything. Add the panel model and the application or software version if the screen still shows them. All of this disappears at restart, and it is exactly what the panel vendor's support line will ask for if the freeze returns, so the record you keep now becomes the diagnosis later.
Does cycling panel power reset the PLC too?
On a standard installation, no: the panel and the controller each have their own supply, so breaking the panel's feed leaves the controller and its outputs untouched. Confirm it on your machine once, before you ever need the restart: find the panel's disconnect on the drawing, trace the conductors, and make sure the panel feed does not pass through the machine's main disconnect or a shared power strip.
Planning information, not legal or engineering advice. Rules differ by place: check codes and permits with your local authority and your licensed trades.