Troubleshooting Missing Restart Buttons on SFC and Equipment Module Faceplates in PCS 7

In SIMATIC PCS 7, the disappearance of the Restart button on Sequential Function Chart (SFC) and Equipment Module (EM) faceplates, frequently accompanied by a yellow warning triangle on the top-left Group Display, occurs when the underlying SFC instance is in an illegal state for resumption, or when WinCC SFC Visualization tags have desynchronized. The Restart command button is dynamically governed by the SFC Operating State Logic (OSL) and is only visible when the phase resides in an interruptible or held state (such as Held or Stopped). If message tags or server data cross-references are broken, the faceplate script cannot evaluate the state word, hiding command buttons. To resolve this, verify the SFC state in CFC, run the OS Project Editor to restore SFC faceplate scripts, and execute a full OS compilation with SFC Visualization enabled.

SFC Operating State Logic (OSL) and Faceplate Button Visibility

In SIMATIC PCS 7 batch operations, Sequential Function Charts (SFC) and Equipment Modules (EM) execute complex procedural logic defined by ISA-88 state models. The execution flow is governed by the standardized Operating State Logic (OSL) state machine. The state machine transitions through discrete operational states: Ready, Starting, Running, Holding, Held, Restarting, Stopping, Stopped, Aborting, Aborted, and Completed.

On the operator station (WinCC OS), SFC instances are operated using standard faceplates (@PG_SFC_*.pdl / @SFC_Control.pdl). To ensure operational safety and prevent conflicting operator commands, the faceplate buttons (Start, Hold, Resume, Restart, Stop, Abort, Reset) are dynamically rendered based on active OSL state bits (Status1, Status2, BA_State). The Restart button is programmed to appear only when the sequence resides in a specific state where restarting the interrupted step or phase is technologically permitted (typically the Held or Stopped state).

Root Causes of Disappearing Restart Buttons and Group Display Faults

When multiple Equipment Modules simultaneously lose their Restart buttons and display a yellow warning triangle on the Group Display (@GroupDisplay), technical evaluation points to three interrelated causes:

SFC Instance Residing in an Un-restartable State: If an SFC sequence encounters an unhandled fault transition and drops directly into the Aborted or Completed state, the Restart command becomes invalid according to OSL rules. In these terminal states, the Restart button is intentionally hidden, and only the Reset button is enabled.
Desynchronized WinCC SFC Visualization Tags: The group display warning indicates that the OS compiler failed to link message event IDs (.MsgEvId) or that the WinCC internal tag structure for SFC visualization (@SFC_...) is out of step with the AS controller. When faceplate scripts cannot read valid status double-words, they fail gracefully by hiding all control buttons to prevent dispatching erroneous commands.
Corrupted Faceplate Scripting After Incomplete OS Project Editor Runs: Modifying graphic resolutions or running an OS update without updating SFC faceplates can leave stale C-actions inside @PG_SFC_Standard.pdl, causing visual controls to clip or render off-screen.

SFC Operating States and Command Transition Matrix

The following table details SFC operating states and permissible operator commands according to PCS 7 OSL rules:

Active SFC StateState DescriptionPermissible CommandsRestart Button VisibilityIdle / ReadyPhase waiting to startStartHidden (Start Enabled)RunningNormal recipe step executionHold, Stop, AbortHidden (Hold/Stop Enabled)Holding / StoppingTransient transition statesAbortHidden (State changing)HeldSequence paused by operator/interlockResume, Restart, AbortVisible & ActiveStoppedSequence halted cleanlyRestart, Reset, AbortVisible & ActiveAborted / CompletedTerminal error or finished statesResetHidden (Only Reset Active)Tag Comm FaultGroup Display yellow warning triangleNone (Command locked)Hidden (Script error)

Step-by-Step Procedure to Restore Missing SFC Faceplate Controls

To restore the Restart button and clear the group display fault on SFC faceplates:

Verify the SFC Operating State in CFC Online:
- In SIMATIC Manager, open the CFC chart hosting the affected SFC Type or SFC instance.
- Switch to online mode and open the SFC chart.
- Inspect the top status bar: Verify the active state. If the state is Aborted or Completed, click Reset on the faceplate to return the SFC to Idle, from which it can be re-started.
- If the phase was tripped by an interlock, clear the interlock condition to permit transition to Held.
Restore Standard SFC Faceplates via OS Project Editor:
- Open the OS project in WinCC Explorer on the Engineering Station.
- Double-click OS Project Editor.
- Under the Basic Data tab, ensure that SFC Visualization pictures are checked for updating.
- Click OK to restore pristine Siemens factory faceplates and C-actions (@PG_SFC*.pdl).
Execute Full AS and OS Compilation:
- In SIMATIC Manager, select the CPU chart folder and execute Chart -> Compile -> Changes Only.
- Right-click the OS project and select Compile.
- In the compile wizard, select Entire project, check Tags and messages, and crucially check the box SFC Visualization.
- Complete compilation and confirm zero errors in the compilation log.
Deploy Server Data and Download to OS Servers:
- In WinCC Explorer, right-click Server Data and select Generate.
- Download the updated OS project to redundant OS servers and clients.
- Open the SFC faceplate in WinCC Runtime; confirm that the group display warning is cleared and the Restart button is restored when in the Held state.

Verification

Verify SFC faceplate operation:
1. In WinCC Runtime, open the faceplate for an Equipment Module; confirm that the group display in the top-left corner shows healthy status (green/grey, zero warning triangles).
2. Command the EM to start; once running, click Hold.
3. Confirm that the EM transitions cleanly into the Held state and that the Restart button becomes immediately visible and enabled.
4. Click Restart; verify that the phase restarts execution from the configured resumption step without errors.

Limitations and Operational Precautions

SFC Type Characteristic Restrictions: If the SFC Type definition explicitly disallows restarting (configured under Characteristics -> Options), the button remains suppressed by design.
Authorization Prerequisites: Operating the Restart button requires WinCC Authorization Level 6 (Process Controlling). Operators with Level 5 will see the button greyed out.
Never Modify Standard @PG_SFC*.pdl Files Directly: Customizing SFC faceplates directly causes scripts to fail during subsequent OS Project Editor runs.

Engineer FAQ

Why did the Restart button disappear while the SFC was running?

The Restart command is only valid when an SFC is paused in the Held or Stopped state. It is hidden during normal Running mode.

What does the yellow triangle on the faceplate group display mean?

It indicates an unacknowledged communication fault, missing message tag (.MsgEvId), or server data package mismatch for that technological point.

Can an SFC be restarted after being Aborted?

No. In the Aborted state, the OSL state machine requires executing a Reset to return to the Idle state before starting over.

Why must 'SFC Visualization' be checked during OS Compile?

Checking SFC Visualization instructs the OS compiler to generate SFC state double-words, step transition tags, and faceplate linkages in WinCC Tag Management.