Troubleshooting WinCC Unified PC Runtime Simulation Start Failure

Overview of WinCC Unified PC Runtime Simulation

WinCC Unified PC Runtime is the SCADA/HMI runtime component of the TIA Portal engineering ecosystem that executes compiled HMI projects on a Windows host. When the same physical PC is used as both the Engineering Station and the Runtime PC, TIA Portal provides a "Start Simulation" command that compiles the project and launches it locally in the Unified Runtime process. This avoids the need for dedicated Unified Comfort Panels (UCPs) during development. When the Runtime PC is a separate machine, the Unified Runtime Engine must be installed there as a Windows service and must match the TIA Portal version exactly.

The most frequently reported failure mode is the inability to start the simulation at all, often surfacing as "Failed to establish a connection to device", "Cannot download", or a silent termination of the runtime child process. These errors do not have a single root cause; they are triggered by version mismatches, missing Runtime Engine components, Windows service misconfigurations, host firewall rules, or corrupted runtime caches. This article consolidates the diagnostic procedure, version alignment rules, and recovery steps required to bring the simulation back online.

WinCC Unified Architecture and Simulation Path

Understanding the data path between TIA Portal and Unified Runtime is essential before debugging. When "Start Simulation" is clicked, the following sequence executes:

1. TIA Portal compiles the HMI project into an RT (runtime) artifact.
2. The artifact is staged into the local runtime cache under %LOCALAPPDATA%\Siemens\Automation\Runtime (single-PC mode) or copied to the configured Runtime PC via RPC.
3. The Unified Runtime service receives a start command via the local management port (default TCP 1344) and reads the staged artifact.
4. The runtime initializes the project, opens the HMI display, and starts serving its HTTPS-based HMI interface on TCP 443 (the localhost UI port).
5. If a PLC simulation is configured, the runtime establishes a connection to PLCSim over its TCP interface and exchanges tag values.

Failure at any of these stages produces a different error. Compile errors prevent step 1. Service or port failures prevent step 3. Configuration errors in the runtime project prevent step 4. PLCSim mismatch errors surface in step 5.

Common Failure Modes and Symptom Matrix

Prerequisites for a Successful Simulation

• TIA Portal version: e.g., V17 Update 3. Verify via TIA Portal menu Help → About TIA Portal.
• WinCC Unified PC Runtime Engine: same version and Update level as TIA Portal, installed locally or on the dedicated Runtime PC.
• Project compatibility: project was created on or upgraded to match the current TIA Portal version. Mixed-version projects compile but fail at runtime startup.
• Compile success: project must compile with zero errors. Warnings are tolerated; errors are not.
• Windows session: simulation must be launched from a desktop session, not Windows Service-only Session 0.
• PLCSim (optional): PLCSim V17/V18 matching the TIA Portal version, installed and licensed, when PLC simulation is required.
• Administrator rights: required for first-time installation, Windows service configuration, and to bypass UAC for runtime child processes.
• Available disk space: minimum 2 GB free on the system drive for runtime cache and temporary staging.

Root Cause 1 — TIA Portal / Runtime Engine Version Mismatch

The Unified Runtime Engine is tightly coupled to the TIA Portal major version and update level. A V17 Update 3 Engineering installation requires a V17 Update 3 Runtime Engine. Earlier updates (V17 Update 2, V17 Update 1, base V17) are rejected at handoff. The error surfaces as "Failed to establish a connection to device" even though the Runtime Engine is installed and the service is running.

Diagnostic Commands

1. Open TIA Portal → Help → About TIA Portal. Note the Version and Build fields, for example V17.0.0.6.
2. Open Windows Control Panel → Programs and Features. Locate "WinCC Unified Runtime" and record its Version column.
3. Compare. The Runtime version must match the TIA Portal version digit-for-digit, including the update level.

Resolution

1. Uninstall the mismatched Runtime Engine from Programs and Features.
2. Mount the TIA Portal installation media corresponding to the Engineering version.
3. Run setup, choose "Install WinCC Unified PC Runtime", select the matching Update level.
4. Reboot the Engineering PC after installation completes.
5. Re-launch TIA Portal and verify the simulation starts.

Root Cause 2 — Missing or Incomplete WinCC Unified Runtime Engine

TIA Portal and the Runtime Engine are separately installable components. A common configuration mistake is installing TIA Portal without ticking the Runtime Engine option during setup, especially when only an HMI engineering seat is intended. The "Start Simulation" command requires the Runtime Engine to be present; otherwise the handoff fails immediately.

Diagnostic Steps

1. Open Control Panel → Programs and Features and search for "WinCC Unified".
2. If only "TIA Portal" appears without a corresponding "WinCC Unified Runtime", the Runtime Engine is missing.
3. If "WinCC Unified Runtime" appears, double-click the entry to verify the installation path is intact and not corrupted by a partial uninstall.

Installation Procedure

1. Insert the TIA Portal installation media.
2. Launch Start.exe and choose the language.
3. Select "Install WinCC Unified PC Runtime".
4. Accept the license agreement and click Next.
5. Confirm the install path (default: C:\Program Files\Siemens\Automation\WinCCUnified).
6. Click Install and wait for completion.
7. Reboot the PC.

Root Cause 3 — Siemens Runtime Service Not Running

The Unified Runtime is hosted under a Windows service. When the service is not running, "Start Simulation" fails with a connection error because there is no process listening on the runtime management port (TCP 1344).

Verification Procedure

1. Press Win + R, type services.msc, and press Enter.
2. Locate the following services:
   • Siemens Runtime Manager
   • Siemens TIA Portal (or Siemens S7-PCT if present)
   • Siemens PLCSim (when PLC simulation is required)
3. Confirm each is in state Running and Startup Type is Automatic.
4. If any are stopped, right-click → Start.
5. If Startup Type is set to "Manual" or "Disabled", change to "Automatic" and restart the PC.

Service Recovery

If a service fails to start, examine Windows Event Viewer → Windows Logs → Application for events with Source "Siemens Runtime Manager" or "Siemens TIA Portal". Common errors include missing dependencies (e.g., .NET Framework, SQL Server Express for WinCC components) or insufficient permissions on the install directory.

Root Cause 4 — Host Firewall and Antivirus Blocking

Windows Defender Firewall and third-party host intrusion prevention systems (HIPS) can block the local TCP traffic between TIA Portal and the Unified Runtime. Although the traffic is loopback (127.0.0.1), some firewall profiles enforce block rules on loopback connections.

Ports to Open

Diagnostic Procedure

1. Temporarily disable third-party antivirus and HIPS.
2. Test simulation start. If it succeeds, the host security product is the cause.
3. Add firewall inbound rules for the Siemens Runtime executable at C:\Program Files\Siemens\Automation\WinCCUnified\Bin\RTM.exe (path varies by version).
4. Re-enable antivirus and confirm the simulation still starts.

Root Cause 5 — Corrupted Runtime Cache

After repeated failed simulation starts, aborted downloads, or anti-virus quarantine actions, the local runtime cache under %LOCALAPPDATA%\Siemens\Automation\Runtime can contain partial or corrupt project artifacts. Subsequent simulation attempts fail because the runtime cannot read or write its staging area.

Cache Reset Procedure

1. Close TIA Portal.
2. Open services.msc, stop the Siemens Runtime Manager service.
3. Verify no RTM.exe, RTShell.exe, or Unified.exe processes are running via Task Manager.
4. In File Explorer, navigate to %LOCALAPPDATA%\Siemens\Automation\Runtime.
5. Delete the Cache, Log, and Project subfolders.
6. Restart the Siemens Runtime Manager service.
7. Re-launch TIA Portal and start simulation.

Root Cause 6 — Separate Runtime PC Misconfiguration

When the Runtime PC is a different machine from the Engineering PC, additional network and permissions checks apply. Misalignment in any of these layers prevents the simulation download.

Checklist for Separate Runtime PC

• Version parity: identical TIA Portal major version and Update level installed on both Engineering and Runtime PCs.
• Network reachability: ping from Engineering PC to Runtime PC succeeds. The PCs are on the same subnet or routing rules allow TCP 443, 1344, 8080.
• Runtime service: "Siemens Runtime Manager" running on Runtime PC with Automatic startup.
• Windows firewall on Runtime PC: inbound rules allow TCP 443, 1344 from the Engineering PC subnet.
• User rights: the Engineering user account must be a member of the Runtime PC's "Siemens TIA Portal" group, or have explicit load rights via SIMATIC Logon.
• Configured target device: in TIA Portal project tree, under Devices → PC Systems → your Runtime PC, the IP address must match the actual Runtime PC.
• Time synchronization: PC clocks within 5 minutes to avoid license token errors.

Resolution Steps

1. Open Command Prompt on the Engineering PC: telnet <runtime-pc-ip> 1344. A blank screen (TCP connect) indicates the management port is open. "Connection refused" indicates firewall or service issue.
2. If telnet is unavailable, use Test-NetConnection -ComputerName <runtime-pc-ip> -Port 1344 in PowerShell.
3. Add the Engineering user to the "Siemens TIA Portal" group on the Runtime PC via Computer Management.
4. Update the device IP in TIA Portal and recompile.
5. Retry simulation download.

Step-by-Step Diagnostic Procedure

Use this ordered checklist when an engineer reports "cannot simulate" or "cannot download". Each step rules out a class of failure before moving to the next.

1. Compile clean: Project → Compile → All. Resolve all errors. Note warnings but proceed.
2. Verify TIA Portal version: Help → About. Note exact version, e.g., V17 Update 3.
3. Verify Runtime Engine version: Programs and Features → "WinCC Unified Runtime". Must match step 2.
4. Verify services: services.msc → Siemens Runtime Manager running and Automatic.
5. Verify licenses: Automation License Manager → "WinCC Unified" entry valid (not in grace period expired).
6. Verify Windows session: Confirm launched from an interactive desktop session, not Session 0.
7. Check Event Viewer: Application log, sources "Siemens", "WinCC Unified". Resolve any recent errors.
8. Temporarily disable antivirus and third-party firewall.
9. Clear runtime cache on Engineering and Runtime PCs.
10. Reboot the Engineering PC to reset all service states.
11. Start Simulation and observe whether the Runtime window opens within 60 seconds.
12. If using PLCSim: Start PLCSim before "Start Simulation". Confirm PLCSim process is running and the HMI connection in the project points to PLCSim's IP.

Verification After Fix

1. Open the project in TIA Portal.
2. Right-click the PC Station → Start Simulation.
3. Within 30–60 seconds, the Unified Runtime window should appear with the configured start screen.
4. Click through configured screens, verify navigation works.
5. If PLCSim is in use, verify tag values are updating from the simulated PLC (check in HMI tag diagnostics).
6. Force a tag change in PLCSim and confirm the HMI reflects the update within 1 second.
7. Open a browser on the same PC and navigate to https://localhost — the runtime's web-based HMI should load.
8. Stop simulation cleanly via TIA Portal "Stop Simulation" to avoid orphan processes.

Project Configuration Settings That Affect Simulation

Edge Cases and Field-Commissioning Notes

PLCSim and Unified on the same PC: PLCSim V17/V18 and Unified Runtime V17/V18 are compatible. Start PLCSim first, wait until the S7-PLCSIM instance shows "RUN", then trigger "Start Simulation" in TIA Portal. Starting in the reverse order produces a transient "connection refused" until PLCSim is fully up.

Concurrent engineers on one Runtime PC: Only one engineering session can hold an active project on the Runtime PC. A second engineer attempting download receives "device is being used by another station". Plan download windows or use dedicated Runtime PCs per engineer.

RDP-launched sessions: Starting TIA Portal over Remote Desktop and triggering simulation can produce display rendering issues because the runtime relies on the local graphics stack. For simulation debugging, prefer a console session or VDI with GPU pass-through.

Windows 11 compatibility: TIA Portal V18 and later are certified for Windows 11. TIA Portal V16/V17 on Windows 11 may require compatibility mode or cumulative updates to start simulation reliably. Verify with the TIA Portal compatibility matrix.

Anti-virus quarantine of staging files: Some endpoint protection products quarantine executable files inside %LOCALAPPDATA%\Siemens\Automation\Runtime on first write. Add the entire Siemens Automation tree to the exclusion list.

Failed update scenarios: After a TIA Portal Update installation, the existing Runtime Engine may be replaced or left at the older update level. Always verify post-update versions and re-run simulation once after Update installation.

Parameter Reference for Simulation Handoff

Recovery from a Non-Recoverable Simulation Failure

If the procedure above does not resolve the failure, escalate to a full component reset:

1. Uninstall "WinCC Unified PC Runtime" from Programs and Features.
2. Uninstall "TIA Portal" if a re-install is needed for full reset.
3. Manually delete residual folders:
   • %LOCALAPPDATA%\Siemens
   • %PROGRAMFILES%\Siemens (after uninstall, residual files may remain)
   • C:\ProgramData\Siemens
4. Reboot the PC.
5. Re-install TIA Portal from media, selecting both "TIA Portal" and "WinCC Unified PC Runtime".
6. Re-install PLCSim if PLC simulation is required.
7. Re-activate licenses via Automation License Manager.
8. Reboot and verify simulation starts with a minimal test project before loading production projects.

FAQ